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Review

Flame Retardant Polypropylenes: A Review

1
Provincial Key Lab of Pulp and Paper Science and Technology and Joint International Research Lab of Lignocellulosic Functional Materials, Nanjing Forestry University, Nanjing 210037, China
2
Department of Polymer Processing, Iran Polymer and Petrochemical Institute, Tehran 14965/115, Iran
3
Université de Lorraine, CentraleSupélec, LMOPS, F-57000 Metz, France
4
Université de Lorraine, IUT de Moselle Est, IUTSGM, 57600 Forbach, France
5
Research and Development Center, Marun Petrochemical Company, Mahshahr 63531 69311, Iran
*
Authors to whom correspondence should be addressed.
Polymers 2020, 12(8), 1701; https://doi.org/10.3390/polym12081701
Submission received: 8 July 2020 / Revised: 27 July 2020 / Accepted: 28 July 2020 / Published: 29 July 2020
(This article belongs to the Special Issue Flame Retardant Polyolefins)

Abstract

:
Polypropylene (PP) is a commodity plastic known for high rigidity and crystallinity, which is suitable for a wide range of applications. However, high flammability of PP has always been noticed by users as a constraint; therefore, a variety of additives has been examined to make PP flame-retardant. In this work, research papers on the flame retardancy of PP have been comprehensively reviewed, classified in terms of flame retardancy, and evaluated based on the universal dimensionless criterion of Flame Retardancy Index (FRI). The classification of additives of well-known families, i.e., phosphorus-based, nitrogen-based, mineral, carbon-based, bio-based, and hybrid flame retardants composed of two or more additives, was reflected in FRI mirror calculated from cone calorimetry data, whatever heat flux and sample thickness in a given series of samples. PP composites were categorized in terms of flame retardancy performance as Poor, Good, or Excellent cases. It also attempted to correlate other criteria like UL-94 and limiting oxygen index (LOI) with FRI values, giving a broad view of flame retardancy performance of PP composites. The collected data and the conclusions presented in this survey should help researchers working in the field to select the best additives among possibilities for making the PP sufficiently flame-retardant for advanced applications.

1. Introduction

Polymers are building blocks of advanced materials and systems, but their flammability has been a serious constraint in their usage in advanced applications [1,2,3]. Polypropylene (PP) is a commodity plastic widely used in a variety of applications, particularly in the form of composites in load-bearing uses due to its high rigidity and crystallinity [4]. By the end of 2020, the PP market size is expected to reach $112 billion, and it is estimated to reach $155 billion by 2026 [5,6]. Its global production was 56.0 million metric tons in 2018, and it is estimated to reach around 88.0 million metric tons by 2026. This growing demand reflects the importance of PP for applications where low density, hardness, high flexural modulus, and chemical resistance are needed [7,8]. Moreover, PP is a low-cost plastic capable of being processed with various methods, e.g., extrusion, thermoforming, and injection molding [9,10]. Therefore, a huge number of PP products, including fibers, films, sheets, textiles, pipes, and profiles, have been developed and used in the automotive, electrical and electronic, packaging, and construction industries [11,12,13,14]. On the other hand, due to the inherent flammability, the use of flame-retardant additives in PP is necessary to minimize the risk of fire [15]. Different types of flame retardants have been used in PP including minerals, phosphorus-based, nitrogen-based, and intumescent [16,17,18]. It was recognized that additive selection plays a crucial role in achieving acceptable flame retardancy [19], where the type, the size, and the loading percentage of flame retardants control the fire behavior of PP matrix.
A diversity of additives are used in PP to make it flame retardant. There is a need for a comprehensive survey to classify PP composites in terms of flame retardancy. In the present paper, several families of flame retardants examined in PP have been identified and categorized to evaluate their flame retardancy performance in terms of Flame Retardancy Index (FRI) [19,20]. FRI is a universal dimensionless index that takes into account well-known parameters obtained from cone calorimeter test (peak of heat release rate (pHRR), the total heat release (THR), and the time to ignition (TTI)). FRI can be simply calculated using Equation (1):
FRI = THR   × pHRR TTI Neat   Polymer THR   × pHRR TTI Composite
Basically, the use of FRI makes it possible to semi-qualitatively classify polymer composites by labeling them as Poor, Good, or Excellent flame retardancy performance and thus enables evaluation of the efficiency of the incorporated flame retardant (FR). There has always been a need for fast-tracking and classifying polymers for their flame retardant performance. The use of FRI made possible classifying polymers and polymer composites in terms of flame retardancy in a simple manner. For FRI values below 100 obtained by the use of Equation (1), we have the case (namely Poor) where the addition of FR adversely affects flame retardancy of polymer. When FRI takes values in the range of 100–101, we name it Good flame retardancy performance, such that addition of FR enhances the resistance of polymer against fire. For FRI values above 101, which is rare in practical cases, we have an Excellent case, where FR significantly improves flame retardancy. It is worth mentioning that some important parameters of testing such as irradiance and sample thickness as well as sample weight can be neglected due to the fact that, in the FRI formula, the parameters related to the neat polymer are divided by those of polymer/FR composite. Thus, the dimensionless value obtained can be used as a reliable measure of the efficiency of FR in polymer. In this survey, the data from the literature were extracted first, and five families of flame retardants that served as PP were considered including phosphorus-based, nitrogen-based, mineral, carbon-based, and bio-based flame retardants, and hybrid cases composed of the aforementioned five categories were distinguished. The main aim of the present survey is to give the readers a broad view of FR systems used in PP via FRI classification method. Certainly, this classification is not a precise and unique data set for FR selection for PP, but it can be considered as a database to compare different systems. The focus of this work was particularly placed on the reports in which cone calorimetry test was carried out. However, some other parameters such as smoke quantity or the percentage of FR elements (phosphorus, nitrogen, …) were not systematically given in this research paper due to the lack of data, which could lead to unreliable judgments. For some papers, limiting oxygen index (LOI) and UL-94 data were also available, which were used in finding possible correlations between the FRI variation and other criteria.

2. Phosphorus-Based Flame Retardants

Various types of phosphorus-based flame retardants have been incorporated into PP to make it flame-retardant [21,22,23]. Table 1 reviews the names and the percentages of these flame retardants incorporated into PP. Moreover, the values obtained from cone calorimetry such as the peak of heat release rate (pHRR), the total heat release (THR), and the time to ignition (TTI) are summarized in this Table. The FRI value, calculated from cone calorimetry parameters, as well as the LOI and UL-94 values, are also presented in Table 1. In some cases, if LOI and/or UL-94 values were not available, the sign “―” was used.
The information provided in Table 1 clearly reveals that APP is quite frequently used as a major phosphorus flame retardant in PP matrix. The percentage of incorporation of phosphorus flame retardants was variable from 10 to 40 wt.%. Figure 1 displays the FRI as a function of wt.% phosphorus-based FR in PP systems. The name/type of each phosphorus flame retardant is provided in the caption of Figure 1. Three formulations reached the Excellent level of flame retardancy, which is quite rare among such data pool. The loading percentage of FR in these formulations varied from 28 to 35 wt.%. Many additives were modified APP and modified phosphorus-nitrogen flame retardants. It can also be speculated that a high loading percentage cannot necessarily guarantee the Excellent level of flame retardancy; besides, the type of phosphorus FR is also an important parameter. Figure 1 also reveals that the majority of points are located in the Good zone of FRI. Therefore, it can be concluded that phosphorus-based flame retardants have quite satisfactorily reinforced PP against flame.
There has always been interest in exploring possible correlations between the data collected from different analyses made on PP materials. Figure 2 shows the flame retardancy performance of phosphorus FR-containing PP in terms of FRI versus the corresponding UL-94 test outcomes. From these data, it is evident that no specified correlation exists between the qualitative results collected from UL-94 and the quantitative ones obtained in cone calorimeter measurements. However, in the case of LOI results, Figure 3 suggests a meaningful relationship can be drawn among data achieved from the calculated FRI and the LOI test results. The LOI value for pure PP is around 17; however, it is increased by addition of flame retardant up to 36, more than a two-fold rise.

3. Nitrogen-Based Flame Retardants

Nitrogen-based flame retardants have also been used in PP to make it resistant against fire. Table 2 gives the names and the percentages of incorporation of these flame retardants, where the data were obtained in cone calorimetry (pHRR, THR, and TTI), FRI calculated from cone calorimetry parameters, as well as LOI and UL-94 values. Some of the nitrogen-based FRs listed in Table 2 also contain a phosphorus element. However, the percentage of nitrogen is more important, and therefore these FRs are listed in this Table.
To give a bright view of the variation trend, Figure 4 illustrates the FRI values as a function of wt.% of nitrogen-based flame retardants incorporated into the PP. The percentage of incorporation was changed from 15 to 40 wt.%. Of note, all points are located in the Good zone of FRI, except two points remarked as Excellent. These two points correspond to a kaolinite additive modified with nitrogen and phosphorus agents. A very noticeable point to be considered is that increasing the amount of diallyldimethylammonium (nominated with the Polymers 12 01701 i022 symbol in Figure 4) from 5 to 25 has no serious effect on the value of FRI, so that they are aligned vertically around FRI values between 1.0 and 2.5. Overall, like what happened to other polymers [77,78], combinatorial flame retardants may be the solution to flammability reduction of PP materials.
Figure 5 patterns UL-94 results as a function of FRI for nitrogen-based flame retardant in PP. It can be observed that even at small quantities of FRI, V0 in UL-94 was achieved. The diversity of data in Figure 5 can be taken as a signature of sensitivity of UL-94 to FRI. Figure 6 shows LOI values as a function of FRI. There is a quite reasonable correlation between the LOI and FRI values, up to FRI value of 6.

4. Mineral-Based Flame Retardants

Mineral additives have been widely used in polymers for their acceptable cost and properties [79]. Mineral-based flame retardants including clays are widely used in PP due to their low cost and acceptable thermal resistance. In this family, the most used flame retardants in volume were aluminum trihydroxide (ATH) and magnesium dihydroxide (MDH). However, due to their low efficiency, a high percentage of loading was necessary for achieving an acceptable level of flame retardancy of polymers. The name and the percentage of the used mineral-based flame retardants in PP are listed in Table 3. Cone calorimetry data, FRI, LOI, and UL-94 values are also given so as to make possible a detailed view on the status of flame retardant efficiency of PP materials.
Figure 7 visualizes the variation of FRI value as a function of flame retardant loading in PP systems (for the convenience of readers, two figures are added for giving a better zoom on data points). This figure clearly shows that even at low loading percentages, it is possible to achieve a relatively high FRI value depending on the type of mineral. There is no denying that some parameters such as the state of dispersion and size of particles are important factors affecting the flame retardant properties.
Unfortunately, the number of papers in which cone calorimetry, UL-94, and LOI values were studied was indeed limited, but the ones available are used plotting Figure 8. It should be noted that no formulation among studied ones is rated at V0. In conclusion, it is quite difficult to find a correlation between quantitative and qualitative parameters based on such a tiny set of data. In regard to the relationship between LOI and FRI, a meaningful trend can still be seen in Figure 9.

5. Carbon-Based Flame Retardants

Carbon-based additives have been widely used in developing polymer composites and nanocomposites [118,119,120,121]. However, due to expense and limited interaction with PP, a few works based on carbon-based flame retardants have been reported on flame-retardant PP materials. Table 4 summarizes all information available on the flame-retardant PP materials containing carbon-based additives.
Figure 10 shows that with low loading percentage (1 wt.%) of carbon nanotubes, it is possible to achieve the Good FRI. No data were available for UL-94 tests. Comparison between Figure 7 and Figure 10 also suggests that low-cost minerals were used at higher loadings, while carbon-based additives were used almost at loadings below 10 wt.%. A limited number of data have also been reported on LOI values. These points are plotted as a function of FRI in Figure 11, where a good correlation can be established between FRI and LOI values. Deeper understanding of the mechanism behind such correlation requires a detailed view of the origin of tests as well as the chemical structure of additives and possible interaction between the PP and additives.

6. Bio-Based Flame Retardants

In recent years, due to sustainability issues, the use of bio-based additives has also been investigated in PP. However, the number of research papers is limited on this subject. Table 5 gives the name and loading percentage of these bio-based FR. The obtained results from cone calorimetry, LOI, and UL-94 tests are also listed in Table 5. Figure 12 and Figure 13 display UL-94 and LOI results as a function of FRI for bio-based flame retardant in PP, respectively.
FRI values are plotted as a function of loading percentage of bio-based FR in Figure 14. It can be observed that a high quantity of bio-based FR, 40 wt.% is needed to achieve FRI equal to 6.

7. Combination of Flame Retardants

As observed in previous sections, using an additive alone can to a limited extent improve flame-retardant properties of PP. Combination of flame retardants is a strategy to improve further the flame retardancy via synergism between various flame retardants [140,141,142]. Moreover, the quantity of the used flame retardant can be reduced in polymer so as to prevent mechanical properties deterioration. Different combinative additive systems were considered in PP. The corresponded data are collected and summarized in Table 6. The third column gives the ratio between flame retardants.
Figure 15 displays the performance of different combinatorial additive systems used for PP. It can be clearly observed from the left-hand side figure that cases with FRI values above 10 (Excellent zone) are more frequent compared to all previous cases in which only one additive was used. More interestingly, the combination of additives appeared a useful strategy where very high FRI values (event more than 50) took place at intermediate loadings (25–30 wt.%). For achieving a high FRI value, the combination of several types of flame retardants is needed, for example, phosphorus, intumescent, and mineral flame retardants [150] or phosphorus, nitrogen, and mineral flame retardants [164].
Figure 16 shows that V-0 level in UL-94 is automatically obtained in the case of combined flame retardant systems used in PP regardless of the FRI value. However, no correlation exists between the FRI and LOI (Figure 17). The complexity of polymer–filler interaction can be considered as the main reason for diversity of properties.

8. Conclusions and Future Perspective

This work opens new avenues to the experts working on “flame retardant polyolefins”, the title of a Special Issue entitled “Flame Retardant Polyolefins” in Polymers journal for which this work is designed and carried out. In this work, more than 150 research papers from the literature dealing with the flame retardancy of PP were analyzed, classified, and discussed in terms of flame retardancy performance. From the selected papers were extracted cone calorimetry data to calculate Flame Retardancy Index (FRI) as a measure or label of flame retardant performance. To have a comprehensive overview of flame retardant PP materials, works on PP flame retardancy were categorized in terms of additives used in classes including: phosphorus-based, nitrogen-based, mineral, carbon-based, bio-based, and hybrid combinatorial flame retardants composed of two or more additives. The analysis of efficiency of flame retardancy was performed in terms of the FRI variation as a function of wt.% of additives used. The analysis quite obviously unveiled the superiority of the combination of additives over the use of each one separately. In addition, the UL-94 and LOI values available in each class of additives were plotted in terms of the FRI so as to find possible correlation between analyses made in the literature. This work provided a pool of data on flame-retardant PP materials for future research on PP materials. It was elucidated that FRI can satisfactorily make possible classification of PP materials in terms of flame retardancy performance. The present work provides those research works that claim achieving synergistic effect of two or more flame retardants with a clear measure of flame retardant performance as Poor, Good, and Excellent labels assigned to PP materials, based on cone calorimetry data. Moreover, future works on LOI and UL-94 tests can be added to the data used here so as to draw a more detailed picture of flame retardancy behavior of PP materials. The approach can be used to make judgement about other flame retardant polyolefins. Moreover, we believe that the mechanical properties of FR polymers should also be considered in the future, but it is pertinent to the completeness of data in the literature. The importance of mechanical properties springs from the fact that highly loaded systems are prone to mechanical failure as a consequence of stress concentration. All in all, the type and the percentage of FRs in polymers affect both the mechanical and flame retardant properties of polymers; therefore, optimization of both properties is of importance.

Author Contributions

Conceptualization, H.V. and M.R.S.; methodology, H.V.; validation, H.V. and M.R.S.; formal analysis, F.S., V.A. and E.M.; investigation, F.D., G.N., V.A. and R.S.; data curation, H.V.; writing—original draft preparation, F.S. and E.M.; writing—review and editing, H.V. and M.R.S.; visualization, H.V. and M.R.S.; supervision, H.V. and M.R.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Acknowledgments

The authors would like to acknowledge Reza Sheibani, the Head of Research & Development Center, Marun Petrochemical Company, Mahshahr, Iran, for providing E.M. with an opportunity to visit petrochemical plant, discussing practical processing criticisms in developing flame-retardant PP, and giving advice on concerns of engineers working on petrochemical plants who intend to make PP flame retardant.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Flame Retardancy Index (FRI) values as a function of phosphorus flame retardant (FR) type and content. Symbols are indicative of different types of phosphorus flame retardant used. Here: APP-10 [24], Polymers 12 01701 i001 APP-12, APP-15 [25], Polymers 12 01701 i002 APP-20 [26], Polymers 12 01701 i003 APP-20 [27], Polymers 12 01701 i004 APP-20 [28], Polymers 12 01701 i005 APP-20 [23], Polymers 12 01701 i006 APP-25 [29], Polymers 12 01701 i007 APP-25 [30], Polymers 12 01701 i008 APP-25 [31], Polymers 12 01701 i009 APP-25 [32], Polymers 12 01701 i010 APP-25 [33], Polymers 12 01701 i011 APP-25 [34], Polymers 12 01701 i012 APP-25, m-APP-25 [35], Polymers 12 01701 i013 APP-25, mc-APP-25 [36], Polymers 12 01701 i014 m-APP-25 [37], Polymers 12 01701 i015 APP-30 [38], Polymers 12 01701 i016 APP-30 [39], Polymers 12 01701 i017 APP-30 [40], Polymers 12 01701 i018 mc-APP-30 [41], Polymers 12 01701 i019 APP-30, mc-APP-30 [42], Polymers 12 01701 i020 APP-30, mc-APP-30 [43], Polymers 12 01701 i021 APP-30, mc-APP-30 [44], Polymers 12 01701 i022 APP-30, mc-APP-5, mc-APP-10, mc-APP-15, mc-APP-20, mc-APP-25, mc-APP-30 [45], Polymers 12 01701 i023 APP-35, m-APP-35 [46], Polymers 12 01701 i024 APP-35, m-APP-35 [47], Polymers 12 01701 i025 APP-40, mc-APP-40 [48], Polymers 12 01701 i026 APP-25, P-CA-25 [49], Polymers 12 01701 i027 APP-25 [50], Polymers 12 01701 i028 APP-IFR-20 [51], Polymers 12 01701 i029 P-IFR-10, P-IFR-15, P-IFR-20, P-IFR-25 [52], Polymers 12 01701 i030 P-IFR-20 [53], Polymers 12 01701 i031 P-IFR-28 [54], Polymers 12 01701 i032 P-IFR-28 [55], Polymers 12 01701 i033 PN-IFR-30 [56], Polymers 12 01701 i034 P-FR-30 [57], Polymers 12 01701 i035 P-FR-20 [58], Polymers 12 01701 i036 DOPO-10 [15], Polymers 12 01701 i037 mc-BDP-10, mc-BDP-20 [59], Polymers 12 01701 i038 OP-20 [60], Polymers 12 01701 i039 AHP-24 [61], Polymers 12 01701 i040 ALPi-30 [62], Polymers 12 01701 i041 PEPA-40 [63].
Figure 1. Flame Retardancy Index (FRI) values as a function of phosphorus flame retardant (FR) type and content. Symbols are indicative of different types of phosphorus flame retardant used. Here: APP-10 [24], Polymers 12 01701 i001 APP-12, APP-15 [25], Polymers 12 01701 i002 APP-20 [26], Polymers 12 01701 i003 APP-20 [27], Polymers 12 01701 i004 APP-20 [28], Polymers 12 01701 i005 APP-20 [23], Polymers 12 01701 i006 APP-25 [29], Polymers 12 01701 i007 APP-25 [30], Polymers 12 01701 i008 APP-25 [31], Polymers 12 01701 i009 APP-25 [32], Polymers 12 01701 i010 APP-25 [33], Polymers 12 01701 i011 APP-25 [34], Polymers 12 01701 i012 APP-25, m-APP-25 [35], Polymers 12 01701 i013 APP-25, mc-APP-25 [36], Polymers 12 01701 i014 m-APP-25 [37], Polymers 12 01701 i015 APP-30 [38], Polymers 12 01701 i016 APP-30 [39], Polymers 12 01701 i017 APP-30 [40], Polymers 12 01701 i018 mc-APP-30 [41], Polymers 12 01701 i019 APP-30, mc-APP-30 [42], Polymers 12 01701 i020 APP-30, mc-APP-30 [43], Polymers 12 01701 i021 APP-30, mc-APP-30 [44], Polymers 12 01701 i022 APP-30, mc-APP-5, mc-APP-10, mc-APP-15, mc-APP-20, mc-APP-25, mc-APP-30 [45], Polymers 12 01701 i023 APP-35, m-APP-35 [46], Polymers 12 01701 i024 APP-35, m-APP-35 [47], Polymers 12 01701 i025 APP-40, mc-APP-40 [48], Polymers 12 01701 i026 APP-25, P-CA-25 [49], Polymers 12 01701 i027 APP-25 [50], Polymers 12 01701 i028 APP-IFR-20 [51], Polymers 12 01701 i029 P-IFR-10, P-IFR-15, P-IFR-20, P-IFR-25 [52], Polymers 12 01701 i030 P-IFR-20 [53], Polymers 12 01701 i031 P-IFR-28 [54], Polymers 12 01701 i032 P-IFR-28 [55], Polymers 12 01701 i033 PN-IFR-30 [56], Polymers 12 01701 i034 P-FR-30 [57], Polymers 12 01701 i035 P-FR-20 [58], Polymers 12 01701 i036 DOPO-10 [15], Polymers 12 01701 i037 mc-BDP-10, mc-BDP-20 [59], Polymers 12 01701 i038 OP-20 [60], Polymers 12 01701 i039 AHP-24 [61], Polymers 12 01701 i040 ALPi-30 [62], Polymers 12 01701 i041 PEPA-40 [63].
Polymers 12 01701 g001
Figure 2. FRI values versus UL-94 test results. Symbols are indicative of different types of phosphorus flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1) may have different vertical quantities, e.g., both reveal V-1 behavior in the UL-94 test, but the upper contains more FR in Polypropylene (PP).
Figure 2. FRI values versus UL-94 test results. Symbols are indicative of different types of phosphorus flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1) may have different vertical quantities, e.g., both reveal V-1 behavior in the UL-94 test, but the upper contains more FR in Polypropylene (PP).
Polymers 12 01701 g002
Figure 3. FRI values of PP as a function of limiting oxygen index (LOI) test results. Symbols are indicative of different types of phosphorus flame retardant used.
Figure 3. FRI values of PP as a function of limiting oxygen index (LOI) test results. Symbols are indicative of different types of phosphorus flame retardant used.
Polymers 12 01701 g003
Figure 4. FRI values as a function of nitrogen FR type and content. Symbols are indicative of different types of nitrogen flame retardant used. Here: MP-40 [63], Polymers 12 01701 i001 MPPK-15, MPPK-20, MPPK-25 [64], Polymers 12 01701 i002 MTP-15, MTP-20, MTP-25, MTP-30, m-MTP-30 [65], Polymers 12 01701 i003 MPyP-30 [57], Polymers 12 01701 i004 MPyP-30, TA-CFA-30 [66], Polymers 12 01701 i005 TA-CFA-30 [39], Polymers 12 01701 i006 TA-CFA-30 [40], Polymers 12 01701 i007 TA-CFA-25 [37], Polymers 12 01701 i008 TA-CFA-25 [32], Polymers 12 01701 i009 TA-CA-ZnO-25 [29], Polymers 12 01701 i010 TA-CA-25 [67], Polymers 12 01701 i011 TA-CA-20 [27], Polymers 12 01701 i012 TA-CA-20 [23], Polymers 12 01701 i013 TA-IFR-20 [68], Polymers 12 01701 i014 TA-IFR-25 [31], Polymers 12 01701 i015 PI-FR-25 [69], Polymers 12 01701 i016 PI-IFR-30 [70], Polymers 12 01701 i017 PI-IFR-20, PI-IFR-30, PI-IFR-40 [71], Polymers 12 01701 i018 NOR116-0.5 [72], Polymers 12 01701 i019 NOR116-0.3 [73], Polymers 12 01701 i020 PPU-CA-25 [50], Polymers 12 01701 i021 N-FR-22, N-FR-25 [74], Polymers 12 01701 i022 N-IFR-5, N-IFR-10, N-IFR-15, N-IFR-20, N-IFR-25 [75], Polymers 12 01701 i023 N-IFR-25 [76], Polymers 12 01701 i024 PN-IFR-30 [56].
Figure 4. FRI values as a function of nitrogen FR type and content. Symbols are indicative of different types of nitrogen flame retardant used. Here: MP-40 [63], Polymers 12 01701 i001 MPPK-15, MPPK-20, MPPK-25 [64], Polymers 12 01701 i002 MTP-15, MTP-20, MTP-25, MTP-30, m-MTP-30 [65], Polymers 12 01701 i003 MPyP-30 [57], Polymers 12 01701 i004 MPyP-30, TA-CFA-30 [66], Polymers 12 01701 i005 TA-CFA-30 [39], Polymers 12 01701 i006 TA-CFA-30 [40], Polymers 12 01701 i007 TA-CFA-25 [37], Polymers 12 01701 i008 TA-CFA-25 [32], Polymers 12 01701 i009 TA-CA-ZnO-25 [29], Polymers 12 01701 i010 TA-CA-25 [67], Polymers 12 01701 i011 TA-CA-20 [27], Polymers 12 01701 i012 TA-CA-20 [23], Polymers 12 01701 i013 TA-IFR-20 [68], Polymers 12 01701 i014 TA-IFR-25 [31], Polymers 12 01701 i015 PI-FR-25 [69], Polymers 12 01701 i016 PI-IFR-30 [70], Polymers 12 01701 i017 PI-IFR-20, PI-IFR-30, PI-IFR-40 [71], Polymers 12 01701 i018 NOR116-0.5 [72], Polymers 12 01701 i019 NOR116-0.3 [73], Polymers 12 01701 i020 PPU-CA-25 [50], Polymers 12 01701 i021 N-FR-22, N-FR-25 [74], Polymers 12 01701 i022 N-IFR-5, N-IFR-10, N-IFR-15, N-IFR-20, N-IFR-25 [75], Polymers 12 01701 i023 N-IFR-25 [76], Polymers 12 01701 i024 PN-IFR-30 [56].
Polymers 12 01701 g004
Figure 5. FRI values versus UL-94 test results. Symbols are indicative of different types of nitrogen flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities; e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Figure 5. FRI values versus UL-94 test results. Symbols are indicative of different types of nitrogen flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities; e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Polymers 12 01701 g005
Figure 6. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of nitrogen flame retardant used.
Figure 6. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of nitrogen flame retardant used.
Polymers 12 01701 g006
Figure 7. FRI values as a function of the mineral FR type and content from close-up and long-shot views. Symbols are indicative of different types of mineral flame retardant used. The diversity and abundance of data were reasons why such different scales were provided for detection of behavior of PP against flame. Here: ATH-50 [80], Polymers 12 01701 i001 ATH-60 [81], Polymers 12 01701 i002 ATH-20, ATH-40, MDH-20, MDH-40 [82], Polymers 12 01701 i003 MDH-40, MDH-60 [82], Polymers 12 01701 i004 MDH-62.5 [83], Polymers 12 01701 i005 MDH-50 [84], Polymers 12 01701 i006 MDH-40 [85], Polymers 12 01701 i007 MDH-30, m-MDH-30, m-MDH-30 [86], Polymers 12 01701 i008 MDH-10, MDH-15 [87], Polymers 12 01701 i009 Kaol-25 [64], Polymers 12 01701 i010 Kaol-0.5, Kaol-1.5, Kaol-3, m-Kaol-0.5, m-Kaol-1.5, m-Kaol-3 [88], Polymers 12 01701 i011 Kaol-1.5, m-Kaol-1.5 [89], Polymers 12 01701 i012 Kaol-10, Kaol-20, Kaol-30, m-Kaol-10, m-Kaol-20, m-Kaol-30, TC-10, TC-20, TC-30 [90], Polymers 12 01701 i013 LDH-0.5, LDH-1, LDH-1.5, m-LDH-0.5, m-LDH-1, m-LDH-1.5, LDH-0.5, LDH-1, LDH-1.5, m-LDH-0.5, m-LDH-1, m-LDH-1.5 [91], Polymers 12 01701 i014 A-LDH-1, A-LDH-2, B-LDH-1, B-LDH-2, B-LDH-4, C-LDH-1, C-LDH-2, C-LDH-4, D-LDH-1, D-LDH-2, D-LDH-4, E-LDH-1, E-LDH-2, E-LDH-4 [92], Polymers 12 01701 i015 A-LDH-1, A-LDH-4, B-LDH-1, B-LDH-4, C-LDH-1, C-LDH-4, D-LDH-1, D-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i016 A-LDH-1, A-LDH-4, B-LDH-1, B-LDH-4, C-LDH-1, C-LDH-4, D-LDH-1, D-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i017 A-LDH-1, A-LDH-4, C-LDH-1, C-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i018 m-LDH-1, m-LDH-3, m-LDH-5 [93], Polymers 12 01701 i019 m-LDH-3, m-LDH-5, m-LDH-10 [94], Polymers 12 01701 i020 LDH-10.7, m-LDH-10.7 [95], Polymers 12 01701 i021 alkyl-NH4Cl-1.2, MMT-5, H-MMT-5, m-MMT-5 [96], Polymers 12 01701 i022 m-MMT-5 [96], Polymers 12 01701 i023 m-MMT-4.75, m-MMT-4.75, m-MMT-4.75 [97], Polymers 12 01701 i024 MMT-10, m-MMT-10 [24], Polymers 12 01701 i025 m-MMT-3, m-MMT-10, m-MMT-16 [98], Polymers 12 01701 i026 MMT-2, m-MMT-2, m-MMT-5, m-MMT-10 [99], Polymers 12 01701 i027 m-MMT-3, m-MMT-8, m-MMT-12 [100], Polymers 12 01701 i028 m-MMT-2.5, m-MMT-5, m-MMT-15, m-MMT-25, m-MMT-2.5, m-MMT-5, m-MMT-15, m-MMT-25 [101], Polymers 12 01701 i029 m-MMT-1, m-MMT-3, m-MMT-5 [102], Polymers 12 01701 i030 Nf-5, m-BT-5 [103], Polymers 12 01701 i031 Nf-5, m-BT-5 [103], Polymers 12 01701 i032 C20A-1, C20A-3, C20A-5 [104], Polymers 12 01701 i033 C15A-5 [60], Polymers 12 01701 i034 C20A-5, C20A-5, TiO2-0.5 [105], Polymers 12 01701 i035 Al2O3-2 [106], Polymers 12 01701 i036 NiFeO-2, CoFeO-2 [107], Polymers 12 01701 i037 Ni2O3-7.5 [108], Polymers 12 01701 i038 Nmm-cat-1, Nmm-cat-2, Nmm-cat-3 [109], Polymers 12 01701 i039 MOSw-30, m-MOSw-30 [110], Polymers 12 01701 i040 MnO-10, Mn2O3-10, MnC2O4-10 [111], Polymers 12 01701 i041 Znacac-1, Cracac-1 [53], Polymers 12 01701 i042 ZrPP-2 [112], Polymers 12 01701 i043 S4SQH-1, S4SQH-5, S4SQH-10, m-S4SQH-1, m-S4SQH-5, m-S4SQH-1, m-S4SQH-5, m-S4SQH-10 [113], Polymers 12 01701 i044 Si-FR-25 [30], Polymers 12 01701 i045 SEP-0.5, m-SEP-0.5 [25], Polymers 12 01701 i046 SEP-5, m-SEP-5 [87], Polymers 12 01701 i047 me-POSS-1.95, me-POSS-6.5, ph-POSS-3.75, ph-POSS-12.5 [114], Polymers 12 01701 i048 T8-POSS-10, Al-POSS-10, Zn-POSS-10 [115], Polymers 12 01701 i049 SA-10 [5], Polymers 12 01701 i050 HNT-8, HNT-W-8 [116], Polymers 12 01701 i051 HNT-8, HNT-W-4, HNT-W-8, HNT-W-16 [116], Polymers 12 01701 i052 HNT-5, HNT-10, HNT-15, m-HNT-5, m-HNT-10, m-HNT-15 [117].
Figure 7. FRI values as a function of the mineral FR type and content from close-up and long-shot views. Symbols are indicative of different types of mineral flame retardant used. The diversity and abundance of data were reasons why such different scales were provided for detection of behavior of PP against flame. Here: ATH-50 [80], Polymers 12 01701 i001 ATH-60 [81], Polymers 12 01701 i002 ATH-20, ATH-40, MDH-20, MDH-40 [82], Polymers 12 01701 i003 MDH-40, MDH-60 [82], Polymers 12 01701 i004 MDH-62.5 [83], Polymers 12 01701 i005 MDH-50 [84], Polymers 12 01701 i006 MDH-40 [85], Polymers 12 01701 i007 MDH-30, m-MDH-30, m-MDH-30 [86], Polymers 12 01701 i008 MDH-10, MDH-15 [87], Polymers 12 01701 i009 Kaol-25 [64], Polymers 12 01701 i010 Kaol-0.5, Kaol-1.5, Kaol-3, m-Kaol-0.5, m-Kaol-1.5, m-Kaol-3 [88], Polymers 12 01701 i011 Kaol-1.5, m-Kaol-1.5 [89], Polymers 12 01701 i012 Kaol-10, Kaol-20, Kaol-30, m-Kaol-10, m-Kaol-20, m-Kaol-30, TC-10, TC-20, TC-30 [90], Polymers 12 01701 i013 LDH-0.5, LDH-1, LDH-1.5, m-LDH-0.5, m-LDH-1, m-LDH-1.5, LDH-0.5, LDH-1, LDH-1.5, m-LDH-0.5, m-LDH-1, m-LDH-1.5 [91], Polymers 12 01701 i014 A-LDH-1, A-LDH-2, B-LDH-1, B-LDH-2, B-LDH-4, C-LDH-1, C-LDH-2, C-LDH-4, D-LDH-1, D-LDH-2, D-LDH-4, E-LDH-1, E-LDH-2, E-LDH-4 [92], Polymers 12 01701 i015 A-LDH-1, A-LDH-4, B-LDH-1, B-LDH-4, C-LDH-1, C-LDH-4, D-LDH-1, D-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i016 A-LDH-1, A-LDH-4, B-LDH-1, B-LDH-4, C-LDH-1, C-LDH-4, D-LDH-1, D-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i017 A-LDH-1, A-LDH-4, C-LDH-1, C-LDH-4, E-LDH-1, E-LDH-4 [92], Polymers 12 01701 i018 m-LDH-1, m-LDH-3, m-LDH-5 [93], Polymers 12 01701 i019 m-LDH-3, m-LDH-5, m-LDH-10 [94], Polymers 12 01701 i020 LDH-10.7, m-LDH-10.7 [95], Polymers 12 01701 i021 alkyl-NH4Cl-1.2, MMT-5, H-MMT-5, m-MMT-5 [96], Polymers 12 01701 i022 m-MMT-5 [96], Polymers 12 01701 i023 m-MMT-4.75, m-MMT-4.75, m-MMT-4.75 [97], Polymers 12 01701 i024 MMT-10, m-MMT-10 [24], Polymers 12 01701 i025 m-MMT-3, m-MMT-10, m-MMT-16 [98], Polymers 12 01701 i026 MMT-2, m-MMT-2, m-MMT-5, m-MMT-10 [99], Polymers 12 01701 i027 m-MMT-3, m-MMT-8, m-MMT-12 [100], Polymers 12 01701 i028 m-MMT-2.5, m-MMT-5, m-MMT-15, m-MMT-25, m-MMT-2.5, m-MMT-5, m-MMT-15, m-MMT-25 [101], Polymers 12 01701 i029 m-MMT-1, m-MMT-3, m-MMT-5 [102], Polymers 12 01701 i030 Nf-5, m-BT-5 [103], Polymers 12 01701 i031 Nf-5, m-BT-5 [103], Polymers 12 01701 i032 C20A-1, C20A-3, C20A-5 [104], Polymers 12 01701 i033 C15A-5 [60], Polymers 12 01701 i034 C20A-5, C20A-5, TiO2-0.5 [105], Polymers 12 01701 i035 Al2O3-2 [106], Polymers 12 01701 i036 NiFeO-2, CoFeO-2 [107], Polymers 12 01701 i037 Ni2O3-7.5 [108], Polymers 12 01701 i038 Nmm-cat-1, Nmm-cat-2, Nmm-cat-3 [109], Polymers 12 01701 i039 MOSw-30, m-MOSw-30 [110], Polymers 12 01701 i040 MnO-10, Mn2O3-10, MnC2O4-10 [111], Polymers 12 01701 i041 Znacac-1, Cracac-1 [53], Polymers 12 01701 i042 ZrPP-2 [112], Polymers 12 01701 i043 S4SQH-1, S4SQH-5, S4SQH-10, m-S4SQH-1, m-S4SQH-5, m-S4SQH-1, m-S4SQH-5, m-S4SQH-10 [113], Polymers 12 01701 i044 Si-FR-25 [30], Polymers 12 01701 i045 SEP-0.5, m-SEP-0.5 [25], Polymers 12 01701 i046 SEP-5, m-SEP-5 [87], Polymers 12 01701 i047 me-POSS-1.95, me-POSS-6.5, ph-POSS-3.75, ph-POSS-12.5 [114], Polymers 12 01701 i048 T8-POSS-10, Al-POSS-10, Zn-POSS-10 [115], Polymers 12 01701 i049 SA-10 [5], Polymers 12 01701 i050 HNT-8, HNT-W-8 [116], Polymers 12 01701 i051 HNT-8, HNT-W-4, HNT-W-8, HNT-W-16 [116], Polymers 12 01701 i052 HNT-5, HNT-10, HNT-15, m-HNT-5, m-HNT-10, m-HNT-15 [117].
Polymers 12 01701 g007aPolymers 12 01701 g007b
Figure 8. FRI values versus UL-94 test results. Symbols are indicative of different types of mineral flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Figure 8. FRI values versus UL-94 test results. Symbols are indicative of different types of mineral flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Polymers 12 01701 g008
Figure 9. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of mineral flame retardant used.
Figure 9. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of mineral flame retardant used.
Polymers 12 01701 g009
Figure 10. FRI values as a function of carbonaceous FR type and content. Symbols are indicative of different types of carbonaceous flame retardant used. Here: GN-2, m-GN-2 [106], Polymers 12 01701 i001 m–rGNO-2, m–rGNO-2 [122], Polymers 12 01701 i002 rGNO-2, m-rGNO-2, m-rGNO-2 [123], Polymers 12 01701 i003 rGNO-2, m-rGNO-2 [112], Polymers 12 01701 i004 GNO-2, m-GNO-0.5, m-GNO-1, m-GNO-2 [124], Polymers 12 01701 i005 GN-2.5, GN-NiO-2.5, GN-NiCexOy-2.5 [125], Polymers 12 01701 i006 rGNO-2, m-rGNO-1, m-rGNO-2, m-rGNO-3 [126], Polymers 12 01701 i007 m-rGNO-20 [58], Polymers 12 01701 i008 EG(ES 350 F5)-10, EG(ES 700 F5)-10, EG(Nyagraph FP)-10, EG(TEG 315)-10, EG(Nyagraph KP251)-10 [127], Polymers 12 01701 i009 CNT-1, m-CNT-0.5, m-CNT-1, m-CNT-2, m-CNT-4 [128], Polymers 12 01701 i010 CNT-1, m-CNT-0.5, m-CNT-1, m-CNT-2 [129], Polymers 12 01701 i011 MWCNT-1, MWCNT-3, MWCNT-5, m-MWCNT-1, m-MWCNT-3, m-MWCNT-5 [130], Polymers 12 01701 i012 MWCNT-1, MWCNT-3 [131], Polymers 12 01701 i013 MWCNT-3 [132], Polymers 12 01701 i014 MWCNT-10, CF-10 [133], Polymers 12 01701 i015 CF-3, CF-8, CB-5 [134], Polymers 12 01701 i016 AC-7.5 [108], Polymers 12 01701 i017 VGCNF-4, VGCNF-8, VGCNF-12 [6].
Figure 10. FRI values as a function of carbonaceous FR type and content. Symbols are indicative of different types of carbonaceous flame retardant used. Here: GN-2, m-GN-2 [106], Polymers 12 01701 i001 m–rGNO-2, m–rGNO-2 [122], Polymers 12 01701 i002 rGNO-2, m-rGNO-2, m-rGNO-2 [123], Polymers 12 01701 i003 rGNO-2, m-rGNO-2 [112], Polymers 12 01701 i004 GNO-2, m-GNO-0.5, m-GNO-1, m-GNO-2 [124], Polymers 12 01701 i005 GN-2.5, GN-NiO-2.5, GN-NiCexOy-2.5 [125], Polymers 12 01701 i006 rGNO-2, m-rGNO-1, m-rGNO-2, m-rGNO-3 [126], Polymers 12 01701 i007 m-rGNO-20 [58], Polymers 12 01701 i008 EG(ES 350 F5)-10, EG(ES 700 F5)-10, EG(Nyagraph FP)-10, EG(TEG 315)-10, EG(Nyagraph KP251)-10 [127], Polymers 12 01701 i009 CNT-1, m-CNT-0.5, m-CNT-1, m-CNT-2, m-CNT-4 [128], Polymers 12 01701 i010 CNT-1, m-CNT-0.5, m-CNT-1, m-CNT-2 [129], Polymers 12 01701 i011 MWCNT-1, MWCNT-3, MWCNT-5, m-MWCNT-1, m-MWCNT-3, m-MWCNT-5 [130], Polymers 12 01701 i012 MWCNT-1, MWCNT-3 [131], Polymers 12 01701 i013 MWCNT-3 [132], Polymers 12 01701 i014 MWCNT-10, CF-10 [133], Polymers 12 01701 i015 CF-3, CF-8, CB-5 [134], Polymers 12 01701 i016 AC-7.5 [108], Polymers 12 01701 i017 VGCNF-4, VGCNF-8, VGCNF-12 [6].
Polymers 12 01701 g010
Figure 11. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of carbon-based flame retardant used.
Figure 11. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of carbon-based flame retardant used.
Polymers 12 01701 g011
Figure 12. FRI values versus UL-94 test results. Symbols are indicative of different types of bio-based flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1) may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Figure 12. FRI values versus UL-94 test results. Symbols are indicative of different types of bio-based flame retardant (FR) used. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1) may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Polymers 12 01701 g012
Figure 13. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of bio-based flame retardant used. The green triangles are related to a mixture of phytic acid and piperazine-based FR. The increase of LOI is directly related to the percentage of FR loading, 15, 18, 20, and 25 wt.%.
Figure 13. FRI values of PP as a function of LOI test results. Symbols are indicative of different types of bio-based flame retardant used. The green triangles are related to a mixture of phytic acid and piperazine-based FR. The increase of LOI is directly related to the percentage of FR loading, 15, 18, 20, and 25 wt.%.
Polymers 12 01701 g013
Figure 14. FRI values as a function of bio-based FR type and content. Symbols are indicative of different types of bio-based flame retardant used. Here: CD-10 [135], Polymers 12 01701 i001 HAandCD-FR-10 [15], Polymers 12 01701 i002 m-lig-20 [136], Polymers 12 01701 i003 PHPI-FR-15, PHPI-FR-18, PHPI-FR-20, PHPI-FR-25 [137], Polymers 12 01701 i004 BC-15, BC-25, BC-30, BC-35 [138], Polymers 12 01701 i005 Wool-40, m-wool-40, m-wool-40, m-CF-40 [28], Polymers 12 01701 i006 CF-40, m-CF-40, m-CF-40 [139].
Figure 14. FRI values as a function of bio-based FR type and content. Symbols are indicative of different types of bio-based flame retardant used. Here: CD-10 [135], Polymers 12 01701 i001 HAandCD-FR-10 [15], Polymers 12 01701 i002 m-lig-20 [136], Polymers 12 01701 i003 PHPI-FR-15, PHPI-FR-18, PHPI-FR-20, PHPI-FR-25 [137], Polymers 12 01701 i004 BC-15, BC-25, BC-30, BC-35 [138], Polymers 12 01701 i005 Wool-40, m-wool-40, m-wool-40, m-CF-40 [28], Polymers 12 01701 i006 CF-40, m-CF-40, m-CF-40 [139].
Polymers 12 01701 g014
Figure 15. FRI values as a function of combinatorial FR additives and their content in PP in long-shot (left-hand figure) and close-up (right-hand figure) views. Symbols are indicative of different types of combinatorial flame retardant used. Here: APP-13.2/PER-6.8 [68], APP-16.7/PER-8.3 [143], Polymers 12 01701 i053 APP-18.7/PER-6.3 [67], Polymers 12 01701 i054 APP-22.5/PER-7.5, mc-(APP-22.5&PER-7.5) [144], Polymers 12 01701 i055 APP-10.5/PER-9.8/MEL-9.1, APP-15.3/PER-9.3/MEL-8.8, APP-19.1/PER-8.9/MEL-8.2 [145], Polymers 12 01701 i056 APP-10.5/PER-9.8/MEL-9.1, APP-15.3/PER-9.3/MEL-8.8, APP-19.1/PER-8.9/MEL-8.2 [145], Polymers 12 01701 i034 APP-15.3/PER-9.3/MEL-8.6, APP-14.3/PER-8.7/MEL-8.1/MDH-6.2 [146], Polymers 12 01701 i019 APP-15.3/PER-9.3/MEL-8.6, APP-14.3/PER-8.7/MEL-8.1/MDH-6.2 [146], Polymers 12 01701 i147 APP-12/PER-4/MEL-4/C20A-1, APP-12/PER-4/MEL-4/C20A-3, APP&MMT-12/PER-4/MEL-4/C20A-1, APP&MMT-12/PER-4/MEL-4/C20A-3 [104] Polymers 12 01701 i148 m-APP-16.6/DPER-4.2/MEL-4.2, m-APP-16/DPER-4/MEL-4/SEP-1 [147], Polymers 12 01701 i149 APP-13.5/PER-4.5, APP-12.75/PER-4.25/MF-1, APP-12.75/PER-4.25/MFA-1 [148], Polymers 12 01701 i066 APP-22.5/PER-7.5 [149], Polymers 12 01701 i002 APP-12.7/PER-5.3, APP-12/PER-5/TA-FR-1 [150], Polymers 12 01701 i057 APP-16.67/PER-8.33, APP-16.33/PER-8.17/NOR116-0.5 [72], Polymers 12 01701 i058 APP-13.5/PER-4.5, APP-12.75/PER-4.25/G-bases-1, APP-12.75/PER-4.25/U-bases-1 [151], Polymers 12 01701 i059 APP-17.2/DPER-7.8, m-APP-17.2/DPER-7.8, APP-16.2/DPER-7.8/ATH-1 [152], Polymers 12 01701 i060 APP-21.4/PER-7.1, APP-20.3/PER-6.8/Kaol-1.4 [70], Polymers 12 01701 i061 APP-21.75/PER-7.25, APP-19.5/PER-6.5/MMT-3, APP-19.5/PER-6.5/m-MMT-3 [153], Polymers 12 01701 i018 APP-21.75/PER-7.25, APP-19.5/PER-6.5/MMT-3, APP-19.5/PER-6.5/m-MMT-3, APP-19.5/PER-6.5/m-MMT-3 [154], Polymers 12 01701 i003 APP-18.75/PER-6.25, APP-18/PER-6/LDH-1, APP-18/PER-6/m-LDH-1 [155], Polymers 12 01701 i062 APP-18.75/PER-6.25, APP-18/PER-6/m-SiR-1, APP-18/PER-6/m-SiR-1, APP-16.5/PER-5.5/m-SiR-3 [156], Polymers 12 01701 i063 m-APP-16.7/DPER-8.3, m-APP-16.7/DPER-8.3/Z-1, m-APP-16.7/DPER-8.3/Z-1/MWCNT-0.1 [157], Polymers 12 01701 i064 APP-18.75/PER-6.25, APP-18.75/PER-6.25/ALL-2 [158], Polymers 12 01701 i065 APP-16.7/PER-8.3, APP-15/PER-7.5/MAO-2.5, APP-15/PER-7.5/Zn-MAO-2.5 [159], Polymers 12 01701 i034 APP-16.7/PER-8.3, APP-16/PER-8/m-SEP-1, APP-15.3/PER-7.7/m-SEP-2, APP-14.7/PER-7.3/m-SEP-3, APP-14/PER-7/m-SEP-4, APP-13.3/PER-6.7/m-SEP-5 [160], Polymers 12 01701 i019 APP-15/PER-5, APP-14.25/PER-4.75/OP-POSS-1, APP-14.25/PER-4.75/A-POSS-1, APP-14.25/PER-4.75/OA-POSS-1, APP-14.25/PER-4.75/TS-POSS-1 [161], Polymers 12 01701 i147 APP-20/PER-10¸ APP-19/PER-9.5/T-RS-5, APP-19/PER-9.5/CV-5, APP-19/PER-9.5/CR-5 [162], Polymers 12 01701 i148 APP-15/PER-5, APP-14.25/PER-4.75/ZnB-1, APP-14.25/PER-4.75/BPO4-1, APP-14.25/PER-4.75/Bsi-1, APP-14.25/PER-4.75/LaB-1 [163], Polymers 12 01701 i149 APP-18.75/PER-6.25, APP-17.25/PER-5.75/NiFeO-2, APP-17.25/PER-5.75/CoFeO-2 [107], Polymers 12 01701 i066 APP-16.67/PER-8.33, APP-15.33/PER-7.67/Ni12P5-2, APP-15.33/PER-7.67/Co2P-2, APP-15.33/PER-7.67/Cu3P-2 [164], Polymers 12 01701 i050 APP-18.75/PER-6.25, APP-18/PER-6/ZHS-1 [165], Polymers 12 01701 i035 APP-18.75/PER-6.25, APP-18.75/PER-6.25/MnAc-1, APP-18.75/PER-6.25/MnAc-2, APP-18.75/PER-6.25/MnAc-3, APP-18.75/PER-6.25/MnAc-4 [166], Polymers 12 01701 i067 APP-21/DPER-7/m-SA-7 [167], Polymers 12 01701 i146 APP-15.4/PEPA-7.6, APP-15.4/PEPA-7.6/NOR116-2, APP-15.4/PEPA-7.6/ZrP-2, APP-15.4/PEPA-7.6/m-ZrP-2 [168], Polymers 12 01701 i020 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [169], Polymers 12 01701 i068 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [170], Polymers 12 01701 i069 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/Kaol nanoroll-1.5 [171], Polymers 12 01701 i051 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [89], Polymers 12 01701 i021 mc-APP-16.7/PEPA-8.3, mc-APP-15.7/PEPA-7.8/Kaol-1.5, mc-APP-15.7/PEPA-7.8/HNT-1.5, mc-APP-15.7/PEPA-7.8/Kaol-1.35/HNT-0.15 [172], Polymers 12 01701 i006 mc-APP-16.7/PEPA-8.3, mc-APP-15.7/PEPA-7.8/Kaol-1.5, mc-APP-15.7/PEPA-7.8/HSA-A-1.5, mc-APP-15.7/PEPA-7.8/HSA-P-1.5, mc-APP-15.7/PEPA-7.8/HSA-A-La-1.5, mc-APP-15.7/PEPA-7.8/HSA-P-La-1.5 [173], Polymers 12 01701 i055 APP-12.5/P-CA-12.5 [49], Polymers 12 01701 i056 APP-28/PhZ-FR-2, APP-26/PhZ-FR-4, APP-24/PhZ-FR-6, APP-22/PhZ-FR-8 [38], Polymers 12 01701 i150 mc-APP-22.5/THEIC-7.5 [41], Polymers 12 01701 i151 APP-16.67/PPU-CA-8.33, APP-12.5/PPU-CA-12.5 [50], Polymers 12 01701 i037 APP-17.6/TA-CFA-4.4, m-APP-17.6/TA-CFA-4.4 [95], Polymers 12 01701 i022 APP-16.7/TA-CFA-8.3 [32], Polymers 12 01701 i052 APP-20/TA-CFA-5, m-APP-20/TA-CFA-5 [37], Polymers 12 01701 i007 APP-20/TA-CFA-10, APP-22.5/TA-CFA-7.5, APP-24/TA-CFA-6 [40], Polymers 12 01701 i070 APP-15/TA-CFA-15, APP-20/TA-CFA-10, APP-22.5/TA-CFA-7.5, APP-24/TA-CFA-6 [39], Polymers 12 01701 i071 APP-15/TA-CFA-5, APP-14.63/TA-CFA-4.87/m-MMT-0.5, APP-14.25/TA-CFA-4.75/m-MMT-1, APP-13.87/TA-CFA-4.63/m-MMT-1.5, APP-13.5/TA-CFA-4.5/m-MMT-2, APP-12.75/TA-CFA-4.25/m-MMT-3 [174], Polymers 12 01701 i072 APP-18.24/TA-CFA-4.56/SiO2-1.2, APP-15.66/TA-CFA-3.91/AHP-3.4/SiO2-1.03 [61], Polymers 12 01701 i073 APP-18.24/TA-CFA-4.56/SiO2-1.2, APP-18.24/TA-CFA-4.56/SiO2-1.2 [175], Polymers 12 01701 i074 APP-20/TA-CFA-5, APP-19.6/TA-CFA-4.9/rGNO-0.5, APP-19.2/TA-CFA-4.8/rGNO-1, APP-18.4/TA-CFA-4.6/rGNO-2 [176], Polymers 12 01701 i075 m-APP-20/TA-CFA-5, m-APP-19.6/TA-CFA-4.9/rGNO-0.5, m-APP-19.2/TA-CFA-4.8/rGNO-1, m-APP-18.4/TA-CFA-4.6/rGNO-2, m-APP-17.6/TA-CFA-4.9/[email protected], m-APP-15.2/m-APP@rGNO-5/TA-CFA-4.8, m-APP-10.4/m-APP@rGNO-10/TA-CFA-4.6 [177], Polymers 12 01701 i076 APP-10/TA-CA-10 [23], Polymers 12 01701 i077 APP-13.33/TA-CA-6.67, APP-15/TA-CA-5 [27], Polymers 12 01701 i078 APP-16.7/TA-CA-8.3 [67], Polymers 12 01701 i079 APP-18.75/TA-CA-6.25, mc-APP-18.75/TA-CA-6.25 [36], Polymers 12 01701 i080 APP-13.33/TA-CA-6.67 [149], Polymers 12 01701 i081 APP-20/TA-CA-10, APP-20/Homo-TA-CA-10 [178], APP-15/TA-CA-15, APP-24/TA-CA-6 [179], APP-16.7/TA-CA-8.3, APP-16.5/TA-CA-8.2/NOR116-0.3 [73], APP-14.7/TA-CA-5.3, APP-14/TA-CA-5/m-MMT-1, APP-12.5/TA-CA-4.5/m-MMT-3 [180], APP-16.72/TA-CFA-4.18/SiO2-1.1, APP-16.72/TA-CFA-4.18/SiO2-1.1 [181], APP-16.7/TA-CA-ZnO-8.3 [29], Polymers 12 01701 i152 APP&TA-IFR-10, APP&TA-IFR-15, APP&TA-IFR-20 [182], Polymers 12 01701 i050 APP-12.5/TA-IFR-12.5, APP-16.67/TA-IFR-8.33, APP-18.75/TA-IFR-6.25 [31], Polymers 12 01701 i035 APP-20/PI-TA-CA-5, APP-20/PI-TA-CA-5 [33], Polymers 12 01701 i005 APP-22.5/PI-IFR-7.5, APP-16.4/PI-IFR-8.2/TA-CFA-5.4 [70], Polymers 12 01701 i082 APP-15/ATH-15, mc-(APP-15&ATH-15) [183], Polymers 12 01701 i020 APP-8/MMT-2, APP-6/MMT-4, APP-8/m-MMT-2, APP-6/m-MMT-4 [24], Polymers 12 01701 i068 APP-15/Nf-5, APP-15/m-BT-5 [103], Polymers 12 01701 i085 APP-15/Nf-5, APP-15/m-BT-5 [103], Polymers 12 01701 i083 APP-15/C15A-5, OP-15/C15A-5 [60], Polymers 12 01701 i084 APP-12/C20A-5/PER-4/MEL-4, APP&MMT-12/C20A-5/PER-4/MEL-4, APP&MMT-6/C20A-5/PER-2/MEL-2, APP&MMT-9/C20A-5/PER-3/MEL-3 [104], Polymers 12 01701 i086 APP-19/m-LDH-1, APP-18/m-LDH-2, APP-17/m-LDH-3 [26], Polymers 12 01701 i087 APP-IFR-18/LDH-2, APP-IFR-16/LDH-4, APP-IFR-18/LDH-2, APP-IFR-16/LDH-4 [51], Polymers 12 01701 i088 APP-12.5/Si-FR-12.5, APP-15/Si-FR-10, APP-13.8/Si-FR-9.2, APP-16.67/Si-FR-8.33, APP-18.75/Si-FR-6.25 [30], Polymers 12 01701 i089 APP-12/SEP-0.5, APP-12/m-SEP-0.5 [25], Polymers 12 01701 i090 APP-22.8/SiO2-1.2 [175], Polymers 12 01701 i091 APP-22/CB-3, APP-20/CB-5, APP-18/CB-7 [34], Polymers 12 01701 i092 APP-7.5/CD-7.5 [135], Polymers 12 01701 i093 P-CA-24/MEL-6 [184], Polymers 12 01701 i094 P-FR-15/MPyP-15 [57], Polymers 12 01701 i095 P-FR-20/GNO-2 [58], Polymers 12 01701 i096 P-IFR-19/Znacac-1, P-IFR-19/Cracac-1 [53], Polymers 12 01701 i097 PN-IFR-29.5/m-MMT-0.5, PN-IFR-29/m-MMT-1, PN-IFR-28.5/m-MMT-1.5, PN-IFR-28/m-MMT-2, PN-IFR-27.5/m-MMT-2.5, PN-IFR-27/m-MMT-3, PN-IFR-26/m-MMT-4, PN-IFR-25/m-MMT-5 [56], Polymers 12 01701 i098 P-IFR-25.5/m-MMT-2.5, P-IFR-25.5/m-LDH-2.5, P-IFR-25.5/A-POSS-2.5, P-IFR-25.5/MWCNT-2.5 [55], Polymers 12 01701 i099 P-IFR-26.5/MWCNT-1.5, P-IFR-25.5/MWCNT-2.5, P-IFR-24.5/MWCNT-3.5 [54], Polymers 12 01701 i100 PA-16/EDA-9 [139], Polymers 12 01701 i101 PPU-CA-12.5/APP-12.5, PPU-CA-16.67/APP-8.33, PPU-CA-18.75/APP-6.25, PPU-CA-20/APP-5 [50], Polymers 12 01701 i102 MP-15/PER-10, MP-15/PER-9/Kaol-1, MP-15/PER-8/Kaol-2 [64], Polymers 12 01701 i103 MP-12.3/PER-7.7, MP-15.4/PER-9.6, MP-11.7/PER-7.3/m-MMT-1, MP-14.7/PER-9.3/m-MMT-1 [185], Polymers 12 01701 i104 MMP-16.64/PER-9.36, MMP-16/PER-9/La2O3-1, MMP-15.36/PER-8.64/La2O3-2, MMP-14.72/PER-8.28/La2O3-3 [186], Polymers 12 01701 i105 MPP-22.5/DPER-7.5, MPP-15/EG-10/DPER-5 [187], Polymers 12 01701 i107 MATMP-16.7/PER-8.3 [143], Polymers 12 01701 i106 MPyP-18.75/PER-6.25, MPyP-17.25/PER-5.75/m-CD-2 [188], Polymers 12 01701 i108 MPyP-15/P-FR-15 [57], Polymers 12 01701 i109 MPyP-22.5/TA-CFA-7.5, MPyP-15/TA-CFA-15, TA-CFA-22.5/MPyP-7.5 [66], Polymers 12 01701 i110 TA-CFA-15/APP-15, TA-CFA-20/APP-10 [39], Polymers 12 01701 i111 TA-CA-10/APP-10 [23], Polymers 12 01701 i112 TA-CA-13.33/APP-6.67 [27], Polymers 12 01701 i113 TA-CA-20/APP-10, TA-CA-15/APP-15 [179], Polymers 12 01701 i114 TA-IFR-12.5/APP-12.5, TA-IFR-16.67/APP-8.33 [31], Polymers 12 01701 i115 TA&APP-IFR-10, TA&APP-IFR-15, TA&APP-IFR-20 [182], Polymers 12 01701 i116 PI-IFR-20/APP-10 [70], Polymers 12 01701 i117 N-FR-24.5/SiO2-0.5, N-FR-22/SiO2-3 [74], Polymers 12 01701 i118 N-IFR-20/PA6-5 [75], Polymers 12 01701 i119 N-IFR-24.5/HGM-0.5, N-IFR-24/HGM-1, N-IFR-23/HGM-2, N-IFR-22/HGM-3 [76], Polymers 12 01701 i120 ATH-15/APP-15, mc-(ATH-15&APP-15) [183], Polymers 12 01701 i121 ATH-55/GB-5, ATH-50/GB-10, ATH-47/GB-10/m-ZrP-3, ATH-44/GB-10/m-ZrP-6, ATH-41/GB-10/m-ZrP-9 [81], Polymers 12 01701 i122 ATH-49/m-MMT-1, ATH-47/m-MMT-3, ATH-45/m-MMT-5 [80], Polymers 12 01701 i123 ATH-20/m-MMT-3, ATH-20/m-MMT-10, ATH-20/m-MMT-17 [82], Polymers 12 01701 i124 MDH-16.6/APP-12.7/PER-7.7/MEL-7.2, MDH-25/APP-11.5/PER-7/MEL-6.5, MDH-31.8/APP-10.4/PER-6.3/MEL-5.9 [146], Polymers 12 01701 i125 MDH-16.6/APP-12.7/PER-7.7/MEL-7.2, MDH-25/APP-11.5/PER-7/MEL-6.5, MDH-31.8/APP-10.4/PER-6.3/MEL-5.9 [146], Polymers 12 01701 i126 MDH-20/m-MMT-17 [82], Polymers 12 01701 i127 MDH-30/m-MMT-10, MDH-40/m-MMT-10, MDH-50/m-MMT-10 [82], Polymers 12 01701 i128 MDH-39/m-MMT-1, MDH-37/m-MMT-3, MDH-35/m-MMT-5 [85], Polymers 12 01701 i129 MDH-45/Cobalt chelate-5, MDH-40/Cobalt chelate-10, MDH-35/Cobalt chelate-15, MDH-30/Cobalt chelate-20 [84], Polymers 12 01701 i130 m-MMT-2.5/SEP-2.5, MDH-10/m-SEP-5, MDH-15/m-SEP-5, MDH-10/m-MMT-2.5/SEP-2.5, MDH-15/m-MMT-2.5/SEP-2.5 [87], Polymers 12 01701 i131 MMT-6/APP-4, MMT-8/APP-2, m-MMT-6/APP-4, m-MMT-8/APP-2 [24], Polymers 12 01701 i132 Si-FR-12.5/APP-12.5 [30], Polymers 12 01701 i133 Ni2O3-7.5/AC-7.5 [108], Polymers 12 01701 i134 SEP-10/MWCNT-2 [189], Polymers 12 01701 i135 C30B-3/ACPB-3, C30B-3/BUPB-3, C30B-3/MEPB-3, C30B-3/PBPA-3 [191], Polymers 12 01701 i136 Si-3/SnCl2-2 [190], Polymers 12 01701 i137 C20A-5/TiO2-0.5, m-C20A-5/TiO2-0.5, m-C20A-10/TiO2-0.5 [105], Polymers 12 01701 i138 CF-5/MWCNT-5 [133], Polymers 12 01701 i139 CB-3/MWCNT-1, CB-5/MWCNT-1, CB-5/MWCNT-3 [131], Polymers 12 01701 i140 CB-5/CF-3 [134], Polymers 12 01701 i141 AC-7.5/Ni2O3-7.5 [108], Polymers 12 01701 i142 PER-10.4/MEL-9.7/APP-5.2 [145], Polymers 12 01701 i143 PER-10.4/MEL-9.7/APP-5.2 [145], Polymers 12 01701 i144 CD-7/TEP-3, CD-10/TEP-5, CD-7.5/APP-7.5 [135], Polymers 12 01701 i145 m-lig-18/Ni(Ac)2-2, m-lig-18/Co- (Ac)2-2, m-lig-18/Zn(Ac)2-2 [136].
Figure 15. FRI values as a function of combinatorial FR additives and their content in PP in long-shot (left-hand figure) and close-up (right-hand figure) views. Symbols are indicative of different types of combinatorial flame retardant used. Here: APP-13.2/PER-6.8 [68], APP-16.7/PER-8.3 [143], Polymers 12 01701 i053 APP-18.7/PER-6.3 [67], Polymers 12 01701 i054 APP-22.5/PER-7.5, mc-(APP-22.5&PER-7.5) [144], Polymers 12 01701 i055 APP-10.5/PER-9.8/MEL-9.1, APP-15.3/PER-9.3/MEL-8.8, APP-19.1/PER-8.9/MEL-8.2 [145], Polymers 12 01701 i056 APP-10.5/PER-9.8/MEL-9.1, APP-15.3/PER-9.3/MEL-8.8, APP-19.1/PER-8.9/MEL-8.2 [145], Polymers 12 01701 i034 APP-15.3/PER-9.3/MEL-8.6, APP-14.3/PER-8.7/MEL-8.1/MDH-6.2 [146], Polymers 12 01701 i019 APP-15.3/PER-9.3/MEL-8.6, APP-14.3/PER-8.7/MEL-8.1/MDH-6.2 [146], Polymers 12 01701 i147 APP-12/PER-4/MEL-4/C20A-1, APP-12/PER-4/MEL-4/C20A-3, APP&MMT-12/PER-4/MEL-4/C20A-1, APP&MMT-12/PER-4/MEL-4/C20A-3 [104] Polymers 12 01701 i148 m-APP-16.6/DPER-4.2/MEL-4.2, m-APP-16/DPER-4/MEL-4/SEP-1 [147], Polymers 12 01701 i149 APP-13.5/PER-4.5, APP-12.75/PER-4.25/MF-1, APP-12.75/PER-4.25/MFA-1 [148], Polymers 12 01701 i066 APP-22.5/PER-7.5 [149], Polymers 12 01701 i002 APP-12.7/PER-5.3, APP-12/PER-5/TA-FR-1 [150], Polymers 12 01701 i057 APP-16.67/PER-8.33, APP-16.33/PER-8.17/NOR116-0.5 [72], Polymers 12 01701 i058 APP-13.5/PER-4.5, APP-12.75/PER-4.25/G-bases-1, APP-12.75/PER-4.25/U-bases-1 [151], Polymers 12 01701 i059 APP-17.2/DPER-7.8, m-APP-17.2/DPER-7.8, APP-16.2/DPER-7.8/ATH-1 [152], Polymers 12 01701 i060 APP-21.4/PER-7.1, APP-20.3/PER-6.8/Kaol-1.4 [70], Polymers 12 01701 i061 APP-21.75/PER-7.25, APP-19.5/PER-6.5/MMT-3, APP-19.5/PER-6.5/m-MMT-3 [153], Polymers 12 01701 i018 APP-21.75/PER-7.25, APP-19.5/PER-6.5/MMT-3, APP-19.5/PER-6.5/m-MMT-3, APP-19.5/PER-6.5/m-MMT-3 [154], Polymers 12 01701 i003 APP-18.75/PER-6.25, APP-18/PER-6/LDH-1, APP-18/PER-6/m-LDH-1 [155], Polymers 12 01701 i062 APP-18.75/PER-6.25, APP-18/PER-6/m-SiR-1, APP-18/PER-6/m-SiR-1, APP-16.5/PER-5.5/m-SiR-3 [156], Polymers 12 01701 i063 m-APP-16.7/DPER-8.3, m-APP-16.7/DPER-8.3/Z-1, m-APP-16.7/DPER-8.3/Z-1/MWCNT-0.1 [157], Polymers 12 01701 i064 APP-18.75/PER-6.25, APP-18.75/PER-6.25/ALL-2 [158], Polymers 12 01701 i065 APP-16.7/PER-8.3, APP-15/PER-7.5/MAO-2.5, APP-15/PER-7.5/Zn-MAO-2.5 [159], Polymers 12 01701 i034 APP-16.7/PER-8.3, APP-16/PER-8/m-SEP-1, APP-15.3/PER-7.7/m-SEP-2, APP-14.7/PER-7.3/m-SEP-3, APP-14/PER-7/m-SEP-4, APP-13.3/PER-6.7/m-SEP-5 [160], Polymers 12 01701 i019 APP-15/PER-5, APP-14.25/PER-4.75/OP-POSS-1, APP-14.25/PER-4.75/A-POSS-1, APP-14.25/PER-4.75/OA-POSS-1, APP-14.25/PER-4.75/TS-POSS-1 [161], Polymers 12 01701 i147 APP-20/PER-10¸ APP-19/PER-9.5/T-RS-5, APP-19/PER-9.5/CV-5, APP-19/PER-9.5/CR-5 [162], Polymers 12 01701 i148 APP-15/PER-5, APP-14.25/PER-4.75/ZnB-1, APP-14.25/PER-4.75/BPO4-1, APP-14.25/PER-4.75/Bsi-1, APP-14.25/PER-4.75/LaB-1 [163], Polymers 12 01701 i149 APP-18.75/PER-6.25, APP-17.25/PER-5.75/NiFeO-2, APP-17.25/PER-5.75/CoFeO-2 [107], Polymers 12 01701 i066 APP-16.67/PER-8.33, APP-15.33/PER-7.67/Ni12P5-2, APP-15.33/PER-7.67/Co2P-2, APP-15.33/PER-7.67/Cu3P-2 [164], Polymers 12 01701 i050 APP-18.75/PER-6.25, APP-18/PER-6/ZHS-1 [165], Polymers 12 01701 i035 APP-18.75/PER-6.25, APP-18.75/PER-6.25/MnAc-1, APP-18.75/PER-6.25/MnAc-2, APP-18.75/PER-6.25/MnAc-3, APP-18.75/PER-6.25/MnAc-4 [166], Polymers 12 01701 i067 APP-21/DPER-7/m-SA-7 [167], Polymers 12 01701 i146 APP-15.4/PEPA-7.6, APP-15.4/PEPA-7.6/NOR116-2, APP-15.4/PEPA-7.6/ZrP-2, APP-15.4/PEPA-7.6/m-ZrP-2 [168], Polymers 12 01701 i020 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [169], Polymers 12 01701 i068 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [170], Polymers 12 01701 i069 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/Kaol nanoroll-1.5 [171], Polymers 12 01701 i051 MCAPP-16.7/PEPA-8.3, MCAPP-15.7/PEPA-7.8/Kaol-1.5, MCAPP-15.7/PEPA-7.8/m-Kaol-1.5 [89], Polymers 12 01701 i021 mc-APP-16.7/PEPA-8.3, mc-APP-15.7/PEPA-7.8/Kaol-1.5, mc-APP-15.7/PEPA-7.8/HNT-1.5, mc-APP-15.7/PEPA-7.8/Kaol-1.35/HNT-0.15 [172], Polymers 12 01701 i006 mc-APP-16.7/PEPA-8.3, mc-APP-15.7/PEPA-7.8/Kaol-1.5, mc-APP-15.7/PEPA-7.8/HSA-A-1.5, mc-APP-15.7/PEPA-7.8/HSA-P-1.5, mc-APP-15.7/PEPA-7.8/HSA-A-La-1.5, mc-APP-15.7/PEPA-7.8/HSA-P-La-1.5 [173], Polymers 12 01701 i055 APP-12.5/P-CA-12.5 [49], Polymers 12 01701 i056 APP-28/PhZ-FR-2, APP-26/PhZ-FR-4, APP-24/PhZ-FR-6, APP-22/PhZ-FR-8 [38], Polymers 12 01701 i150 mc-APP-22.5/THEIC-7.5 [41], Polymers 12 01701 i151 APP-16.67/PPU-CA-8.33, APP-12.5/PPU-CA-12.5 [50], Polymers 12 01701 i037 APP-17.6/TA-CFA-4.4, m-APP-17.6/TA-CFA-4.4 [95], Polymers 12 01701 i022 APP-16.7/TA-CFA-8.3 [32], Polymers 12 01701 i052 APP-20/TA-CFA-5, m-APP-20/TA-CFA-5 [37], Polymers 12 01701 i007 APP-20/TA-CFA-10, APP-22.5/TA-CFA-7.5, APP-24/TA-CFA-6 [40], Polymers 12 01701 i070 APP-15/TA-CFA-15, APP-20/TA-CFA-10, APP-22.5/TA-CFA-7.5, APP-24/TA-CFA-6 [39], Polymers 12 01701 i071 APP-15/TA-CFA-5, APP-14.63/TA-CFA-4.87/m-MMT-0.5, APP-14.25/TA-CFA-4.75/m-MMT-1, APP-13.87/TA-CFA-4.63/m-MMT-1.5, APP-13.5/TA-CFA-4.5/m-MMT-2, APP-12.75/TA-CFA-4.25/m-MMT-3 [174], Polymers 12 01701 i072 APP-18.24/TA-CFA-4.56/SiO2-1.2, APP-15.66/TA-CFA-3.91/AHP-3.4/SiO2-1.03 [61], Polymers 12 01701 i073 APP-18.24/TA-CFA-4.56/SiO2-1.2, APP-18.24/TA-CFA-4.56/SiO2-1.2 [175], Polymers 12 01701 i074 APP-20/TA-CFA-5, APP-19.6/TA-CFA-4.9/rGNO-0.5, APP-19.2/TA-CFA-4.8/rGNO-1, APP-18.4/TA-CFA-4.6/rGNO-2 [176], Polymers 12 01701 i075 m-APP-20/TA-CFA-5, m-APP-19.6/TA-CFA-4.9/rGNO-0.5, m-APP-19.2/TA-CFA-4.8/rGNO-1, m-APP-18.4/TA-CFA-4.6/rGNO-2, m-APP-17.6/TA-CFA-4.9/[email protected], m-APP-15.2/m-APP@rGNO-5/TA-CFA-4.8, m-APP-10.4/m-APP@rGNO-10/TA-CFA-4.6 [177], Polymers 12 01701 i076 APP-10/TA-CA-10 [23], Polymers 12 01701 i077 APP-13.33/TA-CA-6.67, APP-15/TA-CA-5 [27], Polymers 12 01701 i078 APP-16.7/TA-CA-8.3 [67], Polymers 12 01701 i079 APP-18.75/TA-CA-6.25, mc-APP-18.75/TA-CA-6.25 [36], Polymers 12 01701 i080 APP-13.33/TA-CA-6.67 [149], Polymers 12 01701 i081 APP-20/TA-CA-10, APP-20/Homo-TA-CA-10 [178], APP-15/TA-CA-15, APP-24/TA-CA-6 [179], APP-16.7/TA-CA-8.3, APP-16.5/TA-CA-8.2/NOR116-0.3 [73], APP-14.7/TA-CA-5.3, APP-14/TA-CA-5/m-MMT-1, APP-12.5/TA-CA-4.5/m-MMT-3 [180], APP-16.72/TA-CFA-4.18/SiO2-1.1, APP-16.72/TA-CFA-4.18/SiO2-1.1 [181], APP-16.7/TA-CA-ZnO-8.3 [29], Polymers 12 01701 i152 APP&TA-IFR-10, APP&TA-IFR-15, APP&TA-IFR-20 [182], Polymers 12 01701 i050 APP-12.5/TA-IFR-12.5, APP-16.67/TA-IFR-8.33, APP-18.75/TA-IFR-6.25 [31], Polymers 12 01701 i035 APP-20/PI-TA-CA-5, APP-20/PI-TA-CA-5 [33], Polymers 12 01701 i005 APP-22.5/PI-IFR-7.5, APP-16.4/PI-IFR-8.2/TA-CFA-5.4 [70], Polymers 12 01701 i082 APP-15/ATH-15, mc-(APP-15&ATH-15) [183], Polymers 12 01701 i020 APP-8/MMT-2, APP-6/MMT-4, APP-8/m-MMT-2, APP-6/m-MMT-4 [24], Polymers 12 01701 i068 APP-15/Nf-5, APP-15/m-BT-5 [103], Polymers 12 01701 i085 APP-15/Nf-5, APP-15/m-BT-5 [103], Polymers 12 01701 i083 APP-15/C15A-5, OP-15/C15A-5 [60], Polymers 12 01701 i084 APP-12/C20A-5/PER-4/MEL-4, APP&MMT-12/C20A-5/PER-4/MEL-4, APP&MMT-6/C20A-5/PER-2/MEL-2, APP&MMT-9/C20A-5/PER-3/MEL-3 [104], Polymers 12 01701 i086 APP-19/m-LDH-1, APP-18/m-LDH-2, APP-17/m-LDH-3 [26], Polymers 12 01701 i087 APP-IFR-18/LDH-2, APP-IFR-16/LDH-4, APP-IFR-18/LDH-2, APP-IFR-16/LDH-4 [51], Polymers 12 01701 i088 APP-12.5/Si-FR-12.5, APP-15/Si-FR-10, APP-13.8/Si-FR-9.2, APP-16.67/Si-FR-8.33, APP-18.75/Si-FR-6.25 [30], Polymers 12 01701 i089 APP-12/SEP-0.5, APP-12/m-SEP-0.5 [25], Polymers 12 01701 i090 APP-22.8/SiO2-1.2 [175], Polymers 12 01701 i091 APP-22/CB-3, APP-20/CB-5, APP-18/CB-7 [34], Polymers 12 01701 i092 APP-7.5/CD-7.5 [135], Polymers 12 01701 i093 P-CA-24/MEL-6 [184], Polymers 12 01701 i094 P-FR-15/MPyP-15 [57], Polymers 12 01701 i095 P-FR-20/GNO-2 [58], Polymers 12 01701 i096 P-IFR-19/Znacac-1, P-IFR-19/Cracac-1 [53], Polymers 12 01701 i097 PN-IFR-29.5/m-MMT-0.5, PN-IFR-29/m-MMT-1, PN-IFR-28.5/m-MMT-1.5, PN-IFR-28/m-MMT-2, PN-IFR-27.5/m-MMT-2.5, PN-IFR-27/m-MMT-3, PN-IFR-26/m-MMT-4, PN-IFR-25/m-MMT-5 [56], Polymers 12 01701 i098 P-IFR-25.5/m-MMT-2.5, P-IFR-25.5/m-LDH-2.5, P-IFR-25.5/A-POSS-2.5, P-IFR-25.5/MWCNT-2.5 [55], Polymers 12 01701 i099 P-IFR-26.5/MWCNT-1.5, P-IFR-25.5/MWCNT-2.5, P-IFR-24.5/MWCNT-3.5 [54], Polymers 12 01701 i100 PA-16/EDA-9 [139], Polymers 12 01701 i101 PPU-CA-12.5/APP-12.5, PPU-CA-16.67/APP-8.33, PPU-CA-18.75/APP-6.25, PPU-CA-20/APP-5 [50], Polymers 12 01701 i102 MP-15/PER-10, MP-15/PER-9/Kaol-1, MP-15/PER-8/Kaol-2 [64], Polymers 12 01701 i103 MP-12.3/PER-7.7, MP-15.4/PER-9.6, MP-11.7/PER-7.3/m-MMT-1, MP-14.7/PER-9.3/m-MMT-1 [185], Polymers 12 01701 i104 MMP-16.64/PER-9.36, MMP-16/PER-9/La2O3-1, MMP-15.36/PER-8.64/La2O3-2, MMP-14.72/PER-8.28/La2O3-3 [186], Polymers 12 01701 i105 MPP-22.5/DPER-7.5, MPP-15/EG-10/DPER-5 [187], Polymers 12 01701 i107 MATMP-16.7/PER-8.3 [143], Polymers 12 01701 i106 MPyP-18.75/PER-6.25, MPyP-17.25/PER-5.75/m-CD-2 [188], Polymers 12 01701 i108 MPyP-15/P-FR-15 [57], Polymers 12 01701 i109 MPyP-22.5/TA-CFA-7.5, MPyP-15/TA-CFA-15, TA-CFA-22.5/MPyP-7.5 [66], Polymers 12 01701 i110 TA-CFA-15/APP-15, TA-CFA-20/APP-10 [39], Polymers 12 01701 i111 TA-CA-10/APP-10 [23], Polymers 12 01701 i112 TA-CA-13.33/APP-6.67 [27], Polymers 12 01701 i113 TA-CA-20/APP-10, TA-CA-15/APP-15 [179], Polymers 12 01701 i114 TA-IFR-12.5/APP-12.5, TA-IFR-16.67/APP-8.33 [31], Polymers 12 01701 i115 TA&APP-IFR-10, TA&APP-IFR-15, TA&APP-IFR-20 [182], Polymers 12 01701 i116 PI-IFR-20/APP-10 [70], Polymers 12 01701 i117 N-FR-24.5/SiO2-0.5, N-FR-22/SiO2-3 [74], Polymers 12 01701 i118 N-IFR-20/PA6-5 [75], Polymers 12 01701 i119 N-IFR-24.5/HGM-0.5, N-IFR-24/HGM-1, N-IFR-23/HGM-2, N-IFR-22/HGM-3 [76], Polymers 12 01701 i120 ATH-15/APP-15, mc-(ATH-15&APP-15) [183], Polymers 12 01701 i121 ATH-55/GB-5, ATH-50/GB-10, ATH-47/GB-10/m-ZrP-3, ATH-44/GB-10/m-ZrP-6, ATH-41/GB-10/m-ZrP-9 [81], Polymers 12 01701 i122 ATH-49/m-MMT-1, ATH-47/m-MMT-3, ATH-45/m-MMT-5 [80], Polymers 12 01701 i123 ATH-20/m-MMT-3, ATH-20/m-MMT-10, ATH-20/m-MMT-17 [82], Polymers 12 01701 i124 MDH-16.6/APP-12.7/PER-7.7/MEL-7.2, MDH-25/APP-11.5/PER-7/MEL-6.5, MDH-31.8/APP-10.4/PER-6.3/MEL-5.9 [146], Polymers 12 01701 i125 MDH-16.6/APP-12.7/PER-7.7/MEL-7.2, MDH-25/APP-11.5/PER-7/MEL-6.5, MDH-31.8/APP-10.4/PER-6.3/MEL-5.9 [146], Polymers 12 01701 i126 MDH-20/m-MMT-17 [82], Polymers 12 01701 i127 MDH-30/m-MMT-10, MDH-40/m-MMT-10, MDH-50/m-MMT-10 [82], Polymers 12 01701 i128 MDH-39/m-MMT-1, MDH-37/m-MMT-3, MDH-35/m-MMT-5 [85], Polymers 12 01701 i129 MDH-45/Cobalt chelate-5, MDH-40/Cobalt chelate-10, MDH-35/Cobalt chelate-15, MDH-30/Cobalt chelate-20 [84], Polymers 12 01701 i130 m-MMT-2.5/SEP-2.5, MDH-10/m-SEP-5, MDH-15/m-SEP-5, MDH-10/m-MMT-2.5/SEP-2.5, MDH-15/m-MMT-2.5/SEP-2.5 [87], Polymers 12 01701 i131 MMT-6/APP-4, MMT-8/APP-2, m-MMT-6/APP-4, m-MMT-8/APP-2 [24], Polymers 12 01701 i132 Si-FR-12.5/APP-12.5 [30], Polymers 12 01701 i133 Ni2O3-7.5/AC-7.5 [108], Polymers 12 01701 i134 SEP-10/MWCNT-2 [189], Polymers 12 01701 i135 C30B-3/ACPB-3, C30B-3/BUPB-3, C30B-3/MEPB-3, C30B-3/PBPA-3 [191], Polymers 12 01701 i136 Si-3/SnCl2-2 [190], Polymers 12 01701 i137 C20A-5/TiO2-0.5, m-C20A-5/TiO2-0.5, m-C20A-10/TiO2-0.5 [105], Polymers 12 01701 i138 CF-5/MWCNT-5 [133], Polymers 12 01701 i139 CB-3/MWCNT-1, CB-5/MWCNT-1, CB-5/MWCNT-3 [131], Polymers 12 01701 i140 CB-5/CF-3 [134], Polymers 12 01701 i141 AC-7.5/Ni2O3-7.5 [108], Polymers 12 01701 i142 PER-10.4/MEL-9.7/APP-5.2 [145], Polymers 12 01701 i143 PER-10.4/MEL-9.7/APP-5.2 [145], Polymers 12 01701 i144 CD-7/TEP-3, CD-10/TEP-5, CD-7.5/APP-7.5 [135], Polymers 12 01701 i145 m-lig-18/Ni(Ac)2-2, m-lig-18/Co- (Ac)2-2, m-lig-18/Zn(Ac)2-2 [136].
Polymers 12 01701 g015
Figure 16. FRI values versus UL-94 test results. Symbols are indicative of combination of flame retardant (FR) additives used in PP. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Figure 16. FRI values versus UL-94 test results. Symbols are indicative of combination of flame retardant (FR) additives used in PP. The vertical intervals in each category, i.e., V-0, V-1, V-2, and NR, are schematically representative of the amount of additive used. For example, two data distinguished by different symbols having the same or very close FRI values (horizontal quantity) in a given category (e.g., V-1), may have different vertical quantities, e.g., both reveal V-1 behavior in UL-94 test, but the upper contains more FR in PP.
Polymers 12 01701 g016
Figure 17. FRI values of PP as a function of LOI test results in long-shot (left-hand figure) and close-up (right-hand figure). Symbols are indicative of different types of blend flame retardants used. The left-side plot reveals that FRI values above 10 (Excellent zone) took place in several cases, which is in contradiction with all previous cases in which only one additive was used.
Figure 17. FRI values of PP as a function of LOI test results in long-shot (left-hand figure) and close-up (right-hand figure). Symbols are indicative of different types of blend flame retardants used. The left-side plot reveals that FRI values above 10 (Excellent zone) took place in several cases, which is in contradiction with all previous cases in which only one additive was used.
Polymers 12 01701 g017
Table 1. Flame-retardant PP materials containing phosphorus-based (P) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
Table 1. Flame-retardant PP materials containing phosphorus-based (P) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
PP Containing Phosphorus-Based (P) FR *wt.%TTI (s)pHRR
(kW·m−2)
THR
(MJ·m−2)
Irradiance
(kW·m−2)
Sample Thickness (mm)FRILOIUL-94Ref.
141104106350.4[24]
Ammonium polyphosphate (APP)102492592350.42.35[24]
54161010635320.8NR[25]
APP1237510973532.3622.3V-2[25]
APP1527339893532.8225.4V-0[25]
341294154.250419NR[26]
APP2021306141.65042.8427NR[26]
481351107353.218.5NR[27]
APP204078792353.21.6620.5NR[27]
24.31388.380.3502.4NR[28]
APP2019.3254.854.5502.46.37V-0[28]
6663344.235317NR[23]
APP203142438.63530.8021NR[23]
18145715650319NR[29]
APP252014551485031.1721.9V-2[29]
259811475017.6NR[30]
APP2518579109501.6423.2NR[30]
4898888.3353.217NR[31]
APP254365280353.21.4921NR[31]
208099650317.6NR[32]
APP2511397875031.2320.6NR[32]
211242111503.218.6NR[33]
APP2521979107503.21.3121.7NR[33]
351203197.650618.2NR[34]
APP2533390.81965062.9220.9NR[34]
25841.689.150318NR[35]
APP2513473.390.25030.9120NR[35]
Piperazine-modified APP (m-APP)2517162.684.55033.7132.5V-0[35]
33141621950617NR[36]
APP25195261805061.8819.6NR[36]
Polysiloxane shell-coated APP (mc-APP)25192141375066.0825NR[36]
45759.298.835317NR[37]
Melamine and phytic acid-modified APP (m-APP)2533218.180.63533.1222.5V-2[37]
371284121503[38]
APP30227671115031.0821.7NR[38]
4898888.335317NR[39]
APP303245977.63531.6322NR[39]
50135091.235317NR[40]
APP305885174.43532.2522NR[40]
331238123.750317.8NR[41]
Melamine-formaldehyde-tris(2-hydroxyethyl) isocyanurate resin microencapsulated APP (mc-APP)3024375116.45032.5532V-0[41]
4483115835317.5NR[42]
APP30304321143531.8122NR[42]
Dipentaerythritol and 4,4′ diphenylmethanediisocyanate and melamine microencapsulated APP (mc-APP)30273001003532.6832.1V-0[42]
29118621550617NR[43]
APP30185431805061.6120.1NR[43]
Epoxy acrylate microencapsulated APP (mc-APP)30133321495062.3124.8NR[43]
401174.7102.235317NR[44]
APP3038526.580.63532.6820NR[44]
4,4′-diphenylmethane diisocyanate and melamine and pentaerythritol microencapsulated APP (mc-APP)3030301.865.13534.5825V-1[44]
68577.582.735318.2NR[45]
APP3041201.144.53533.2120.1NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)557395.467.23531.5018.7NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)1042282.563.73531.6319.6NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)1540214.959.93532.1820NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)2032193.657.33532.0220.3NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)2530145.464.13532.2622.2NR[45]
Thermoplastic polyurethane microencapsulated APP (mc-APP)3031140.641.83533.7022.9NR[45]
25841.689.150318NR[46]
APP3511435.983.95030.9020.4NR[46]
Ethylenediamine-modified APP (m-APP)3511156.160.55033.4930.5V-0[46]
25841.689.150318NR[47]
APP3511435.983.95030.9020.4NR[47]
Ethanolamine-modified APP (m-APP)351896.622.650324.7335V-0[47]
3383721250617NR[48]
APP40304401865061.9720.8NR[48]
Pentaerythritol triacrylate microencapsulated APP (mc-APP)40322141835064.3930.5V-0[48]
38128421450618.2NR[49]
APP25345371775062.5820.9NR[49]
Phosphorus-based charring agent: 3,9-Bis-(1-oxo-2,6,7-trioxa-1-phospha-bicyclo[2,2,2]oct-4-ylmethoxy)-2,4,8,10-tetraoxa-3,9 diphospha-spiro[5.5]undecane 3,9-dioxide (P-CA)25354801685063.1322.6NR[49]
4283111235318NR[50]
APP2536.4578833531.6821NR[50]
361373174.850318.5NR[51]
APP-based intumescent flame retardant (APP-IFR)2022326149.95033.0029.5V-0[51]
2886530.735518.4NR[52]
Phosphorus-based IFR: Six(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-4-methyl) cyclotriphosphazene (P-IFR)102859528.23551.5819.7NR[52]
Phosphorus-based IFR: Six(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-4-methyl) cyclotriphosphazene (P-IFR)153051525.83552.1422.8NR[52]
Phosphorus-based IFR: Six(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-4-methyl) cyclotriphosphazene (P-IFR)2033433233553.1426.1V-2[52]
Phosphorus-based IFR: Six(1-oxo-2,6,7-trioxa-1-phosphabicyclo[2,2,2]octane-4-methyl) cyclotriphosphazene (P-IFR)253540719.53554.1829.4V-0[52]
3039044351.617.4[53]
Phosphorus-based IFR: Poly (4,4-diamino diphenyl methane Obicyclicpentaerythritol phosphate-phosphate) (P-IFR)202422427351.62.2625[53]
3736356353[54]
Phosphorus-based IFR: compound containing Phosphorus(22%) and Nitrogene(18%) (P-IFR)2833622435312.18[54]
3736356353[55]
Phosphorus-based IFR: compound containing Phosphorus(22%) and Nitrogene(18%) (P-IFR)2833622435312.18[55]
299801365018.5[56]
Phosphorus and Nitrogene-based IFR302222993504.7436.3[56]
651416.6128.5353NR[57]
Phosphorus-based flame retardant: Tri (1-oxo-2,6,7-trioxa-1-phosphabicyclo [2,2,2] octane-methyl) phosphate (P-FR)3038640.2104.83531.58NR[57]
54119997.835[58]
Phosphorus-based FR: Poly(4,4-diaminodiphenyl methane spirocyclicpentaerythritol bisphosphonate) (P-FR)206962078.5353.07[58]
611026166354[15]
9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)10606481413541.83[15]
84100096353[59]
Tetraethyl orthosilicate microencapsulated bisphenol-A bis (diphenyl phosphate) (mc-BDP)10578081013530.79[59]
Tetraethyl orthosilicate microencapsulated BDP (mc-BDP)2060932933530.79[59]
44117287.1352.518.1NR[60]
Organic phosphinate (OP)2046105284.2352.51.2020.1V-2[60]
341052.490.850317.5NR[61]
Aluminum hypophosphite (AHP)2423267.177.35033.13[61]
664809335317[62]
Aluminium phosphinate (ALPi)307352489.83531.0426[62]
441175106353[63]
Pentaerythritol phosphate (PEPA)4035776813531.57[63]
Table 2. Flame retardant PP materials containing nitrogen-based (N) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame-retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
Table 2. Flame retardant PP materials containing nitrogen-based (N) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame-retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
PP Containing Nitrogen-Based (N) FR *wt.%TTI
(s)
pHRR
(kW·m−2)
THR
(MJ·m−2)
Irradiance
(kW·m−2)
Sample Thickness (mm)FRILOIUL-94Ref.
441175106353[63]
Melamine phosphate (MP)4039296783534.78[63]
54930140354NR[64]
Melamine salt of pentaerythritol phosphate kaolinite (MPPK)1530208703544.96NR[64]
MPPK20281484235410.86V-0[64]
MPPK25341303335419.10V-0[64]
3092913450317NR[65]
Melamine salt of tripentaerythriol phosphate (MTP)15224801015031.88[65]
MTP2022267915033.7528V-1[65]
MTP2522226735035.5332V-0[65]
MTP3022219725035.7835V-0[65]
Methyl hydrogen siloxane modified MTP (m-MTP)3021253725034.7830V-0[65]
651417128.5353NR[57]
Melamine pyrophosphate (MPyP)3036437103.13532.23NR[57]
34172711235317NR[66]
MPyP3019511833532.5425.5NR[66]
Triazine-based charring foaming agent: synthesized by reaction of cyanuric chloride and ethanolamine and ethylenediamine (TA-CFA)3013584963531.3124NR[66]
4898888.335317NR[39]
Triazine-based CFA: synthesized by reaction of cyanuric chloride and piperazine (TA-CFA)303446886.63531.5220.5V-1[39]
50135091.235317NR[40]
Triazine-based CFA: synthesized by polycondensation of 2-chloro-4,6-di-(2-hydroxyethylamino)-s-triazine (TA-CFA)303851886.73532.0823.5NR[40]
45759.298.835317NR[37]
Triazine-based CFA: synthesized from a macromolecular triazine derivative containing hydroxyethylamino and triazine rings and ethylenediamino groups (TA-CFA)2534487.491.63531.2621.9NR[37]
208099650317.6NR[32]
Triazine-based CFA: Poly[N4-bis(ethylenediamino)-phenyl phosphonic-N2, N6-bis(ethylenediamino)-1,3,5-triazine-N-phenyl (TA-CFA)2512529885031.0020.6NR[32]
18145715650319NR[29]
Triazin-based CA—Zinc oxide (TA-CA-ZnO)25176941495032.0718.3NR[29]
41840.3115.735316.4NR[67]
Triazin-based CA: Poly(ethanediamine-1,3,5-triazine-p-4-amino-2,2,6,6-tetramethylpiperidine) (TA-CA)2530684106.73530.9717.8NR[67]
481351107353.218.5NR[27]
Triazin-based CA: compound containing pentaerythritol and triazine structure (TA-CA)204299498353.21.2922NR[27]
6663344.235317NR[23]
Triazin-based CA: synthesized by
reaction of tris (2-hydrooxyethyl) isocyanurate and 2-carboxyethyl (phenyl) phosphinic acid (TA-CA)
203141737.63530.8322NR[23]
311239123.650318.5NR[68]
Triazin-based IFR: synthesized by
reaction of tris(2-hydroxyethyl) isocyanurate and polyphosphoric acid and melamine (TA-IFR)
2018289.9895033.4429.3V-0[68]
4898888.3353.217NR[31]
Triazin-based IFR: synthesized by
reaction of cyanuric chloride
and N-amino ethylpiperazine (TA-IFR)
253850486.6353.21.5823V-1[31]
20904.4126.250318NR[69]
Piperazine-based FR: synthesized by
reaction of diphenylphosphinyl chloride and piperazine (PI-FR)
2558487.787.55037.7527V-0[69]
451269146.450317.5NR[70]
Piperazine-based IFR: Piperazine spirocyclic phosphoramidate (PI-IFR)3017240.4120.25032.4230.5V-0[70]
4780210435318NR[71]
Piperazine-based IFR: synthesized by
reaction of phosphorus chloride and 2,6,7-trioxa-l-phosphabicyclo[2,2,2]-octane-4-methanol and anhydrous piperazine (PI-IFR)
2036275783532.9724NR[71]
Piperazine-based IFR: synthesized by
reaction of phosphorus chloride and 2,6,7-trioxa-l-phosphabicyclo[2,2,2]-octane-4-methanol and anhydrous piperazine (PI-IFR)
3037209743534.2427NR[71]
Piperazine-based IFR: synthesized by
reaction of phosphorus chloride and 2,6,7-trioxa-l-phosphabicyclo[2,2,2]-octane-4-methanol and anhydrous piperazine (PI-IFR)
4037162603536.7529V-0[71]
36799.3170.935418NR[72]
N-alkoxy hindered amine (NOR116)0.544738.8156.53541.4419NR[72]
3679917035417.5NR[73]
NOR1160.3447381563541.4419.5NR[73]
4283111235318NR[50]
Polyurethane containing Phosphorus-based CA (PPU-CA)2527.3475833531.5329NR[50]
421025137.7354[74]
Nitrogen-based FR: compound containing Nitrogen (27.5.wt.%) and Phosphorus (15.6 wt.%) (N-FR)222217050.33548.6432V-1[74]
Nitrogen-based FR: compound containing Nitrogen (27.5 wt.%) and Phosphorus (15.6 wt.%) (N-FR)252116049.13548.9834V-0[74]
301093108.250318NR[75]
Nitrogen-based IFR: Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexe-based IFR (N-IFR)528968.5103.45031.1020.2NR[75]
Nitrogen-based IFR: Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexe-based IFR (N-IFR)1025626.297.15031.6222NR[75]
Nitrogen-based IFR: Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexe-based IFR (N-IFR)1523543.194.35031.7624.4NR[75]
Nitrogen-based IFR: Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexe-based IFR (N-IFR)2021443.990.15032.0626.3NR[75]
Nitrogen-based IFR: Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexe-based IFR (N-IFR)2518335.383.95032.5227.5V-2[75]
25874.189.350318NR[76]
Nitrogen-based IFR: compound containing Nitrogen (23%) and Phosphorus (21%) (N-IFR)251294.968.25035.7833V-0[76]
299801365018.5[56]
Phosphorus and Nitrogene based IFR302222993504.7436.3[56]
Table 3. Flame-retardant PP materials containing mineral-based (M) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame-retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
Table 3. Flame-retardant PP materials containing mineral-based (M) flame retardants. Data are extracted from the literature: cone calorimetry parameters (TTI, pHRR, THR), LOI, and UL-94 values. The FRI values were calculated by authors of the present review. The name and the percentage of flame retardants are provided in separate columns. “wt.%” was used for loading level of additives, while “―” stands for the systems free of additive or the neat PP. * FR means flame retardant. Since all comparisons were made in terms of FRI, classification of polymers in terms of their flame-retardant properties was not surveyed based on the chemistry of additives, heat flux, sample thickness, etc.
PP Containing Mineral-Based (M) FR *wt.%TTI
(s)
pHRR
(kW·m−2)
THR (MJ·m−2)Irradiance
(kW·m−2)
Sample Thickness (mm)FRILOIUL-94Ref.
371425121.450317.3NR[80]
Aluminum trihydroxide (ATH)505253996.65034.6623.6NR[80]
32147017550418[81]
ATH6034280985049.9625.6[81]
261967112503[82]
ATH2027817905033.11[82]
ATH4028467705037.25[82]
Magnesium dihydroxide (MDH)20311000985032.68[82]
MDH4034433755038.87[82]
30168489503[82]
MDH403377715030.55[82]
MDH60292285150312.46[82]
63.2521.3549.830[83]
MDH62.581.1115.575.7303.81[83]
712283218351[84]
MDH50977892383513.62[84]
381425121.450317.5NR[85]
MDH404654899.15033.8523.3NR[85]
29166033.4351[86]
MDH303998928.33512.66[86]
Dodecanoic acid-treated MDH (m-MDH)303288228.73512.41[86]
Dodecylphosphate treated MDH (m-MDH)302965128.83512.95[86]
3758475.6503[87]
MDH103347165.95031.26[87]
MDH153138161.25031.58[87]
54930140354NR[64]
Kaolinite (Kaol)25324631163541.43NR[64]
29147414250318NR[88]
Kaol0.52814291425030.9918.3NR[88]
Kaol1.52713461405031.0318.3NR[88]
Kaol32612791355031.0818.4NR[88]
Ammonium sulfamate intercalated kaol
(m-Kaol)
0.52713891415030.9918.4NR[88]
Ammonium sulfamate intercalated kaol
(m-Kaol)
1.52811691335031.2918.6NR[88]
Ammonium sulfamate intercalated kaol
(m-Kaol)
32710791265031.4318.7NR[88]
2714741425018NR[89]
Kaol1.5271346140501.1118.3NR[89]
Ammonium sulfamate intercalated Kaol
(m-Kaol)
1.5281169133501.3918.6NR[89]
44100014550[90]
Kaol1035634144501.26[90]
Kaol2038396136502.33[90]
Kaol3041348126503.08[90]
Trisilanolisooctyl polyhedral oligomeric silsesquioxane modified kaol (m-Kaol)1035850140500.96[90]
Trisilanolisooctyl polyhedral oligomeric silsesquioxane modified kaol (m-Kaol)2038650141501.36[90]
Trisilanolisooctyl polyhedral oligomeric silsesquioxane modified kaol (m-Kaol)3050430137502.79[90]
Talc (TC)1049377128503.34[90]
TC2056341118504.58[90]
TC3050295112504.98[90]
451831.96110.850[91]
Ni-Al layered double hydroxide (LDH)0.5531635.53106.8501.36[91]
Ni-Al LDH (LDH)1921430.59117.8502.46[91]
Ni-Al LDH (LDH)1.5411266.66129.1501.13[91]
Organically modified Ni-Al LDH (m-LDH)0.5591116.3770.2503.39[91]
Organically modified Ni-Al LDH (m-LDH)1451026.8681.24502.43[91]
Organically modified Ni-Al LDH (m-LDH)1.5491254.95111.1501.58[91]
Cu-Al LDH (LDH)0.5451026.8681.2502.43[91]
Cu-Al LDH (LDH)1571276.46123501.63[91]
Cu-Al LDH (LDH)1.5501449.98121.8501.27[91]
Organically modified Cu-Al LDH (m-LDH)0.569985.91120502.63[91]
Organically modified Cu-Al LDH (m-LDH)1541175.99121.6501.70[91]
Organically modified Cu-Al LDH (m-LDH)1.5541345.14114.3501.58[91]
201849121503[92]
Mg-Al LDH with mole ratio: Zn:Mg:Al/0:2:1 (A-LDH)11519811415030.60[92]
A-LDH21617641395030.73[92]
Zn-Mg-Al LDH with mole ratio: Zn:Mg:Al/0.5:1.5:1 (B-LDH)11419971365030.57[92]
B-LDH21415121335030.77[92]
B-LDH41311531285030.98[92]
Zn-Mg-Al LDH with mole ratio: Zn:Mg:Al/1:1:1 (C-LDH)11820041355030.74[92]
C-LDH21415461325030.76[92]
C-LDH41212251255030.87[92]
Zn-Mg-Al LDH with mole ratio: Zn:Mg:Al/1.5:0.5:1 (D-LDH)11819381355030.76[92]
D-LDH21516561305030.77[92]
D-LDH41312941235030.91[92]
Zn-Al LDH with mole ratio: Zn:Mg:Al/2:0:1 (E-LDH)11619771365030.66[92]
E-LDH21715431135031.09[92]
E-LDH41413821265030.89[92]
172380140503[92]
A-LDH12019061355031.52[92]
A-LDH41611371295032.13[92]
B-LDH11717151345031.44[92]
B-LDH41710251245032.62[92]
C-LDH11618751305031.28[92]
C-LDH4149921255032.21[92]
D-LDH11520081355031.08[92]
D-LDH4169971265032.49[92]
E-LDH11717961350314.27[92]
E-LDH4167571255033.31[92]
261975125503[92]
A-LDH12118311495030.73[92]
A-LDH42312741275031.34[92]
B-LDH12318381355030.88[92]
B-LDH41810171265031.33[92]
C-LDH12016761375030.82[92]
C-LDH4179811245031.32[92]
D-LDH11918331365030.72[92]
D-LDH4