Stability Improvement of Irradiated Polymer Composites by Inorganic Compounds—A Pertinent Solution with Respect to Phenolic Antioxidants

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions or corrections highlighted in red changes in the re-submitted file. In this round of replies the modifications are inserted. We also reread the text for the elimination of typos.

2. Questions for General Evaluation

Reviewer’s Evaluation

Response and Revisions

2.1. The manuscript was improved by the additional phrases, which are highlighted in red word. They concern the background understanding and the readers’ perception.

Can be improved

Round 1 of comments

Abstract: A significant improvement of stability simultaneously associated with the enhancing functional characteristics, the lack of migration, a low cost and easy accessibility make appropriate the reevaluation of certain fillers as stabilizers. The correlation between the functional properties and the filler nature in polymer materials may be reconsidered for the assessment of the participation capability of inorganic structures in the inhibition of oxidation by the inactivation of free radicals. The life times of degradation intermediates extended by the activities of inorganic compounds are increased by means of electrical interactions involving the unpaired electrons of molecular fragments. These physical contributions are reflected onto chemical stability. The essential feature for the presented inorganic options is the strong impact on the recycling technologies of polymers by radiation processing. The plastic products including all categories of macromolecular materials can gain a widened durability by the inorganic alternative of protection.

Introduction - Page 1

However, the presence of polarizing branches influences the breaking bonds [6] that trigger the chain splitting. The physical characteristics related to the structural peculiarities may distinguish the inorganic compounds heaving the protection features from the “classical” antioxidants.

The modern technologies based on the radiation effects are more and more frequently applied due to its conversion potential.

Introduction - Page 2

This option was preferred because it is the accurate tool used for the appropriation proves of protection suitability. The accumulation of oxygenated intermediates [22] leads to the proportional photon emission, whose chemiluminescence (CL) intensity dependencies on time or temperature allow to qualification of radiation strength, antioxidant efficiencies or substituent effects on the material durability…..

Introduction - Page 3

The proportionality between the measured CL intensity and the accumulated amount of peroxyl radicals is the background in the estimation of polymer degradability.

Mechanistic approach - Page 4

This type of defects may appear either by the scission of a bond as it is occurred in the powder of POSS (polyhedral oligomeric silsesquioxane), an inorganic structure based on the intercalation of -Si-O- units, under the influence of certain substituents [38], by the deterioration of a ligand belonging to a complex structure [39] or by the effects of the doping metallic atoms in the modified oxide filler [40].

Polymer systems improved by inorganic protectors. Page 5

Various configurations with different electronic densities were obtained for the stability testing. Six different structures were added into ethylene-propylene-diene monomer (EPDM) [53]. The evolution of carbonyl radiochemical yields (Fig. 5) indicates the availability of studied structures to confine the oxidation process initiated by the radiolysis of polymer support (EPDM). This yield, G_carbonyl is a radiolysis characteristic that describe how many indicated entities are appeared by absorption of 100 eV.

Polymer systems improved by inorganic protectors. Page 6

So, the oxidation induction time (OIT) is the early stage of degradation, when the oxidation advances very slowly so that its rate may be under the experimental limit. The longer the OIT, the higher the material stability,

Polymer systems improved by inorganic protectors. Page 7

The carbonyl index, the ratio between the absorbance of 1720 cm^-1, the stretching band of carbonyls, and the absorbance at 1460 cm^-1 as reference based on its major proportion in the degrading material in respect with the appearing functions (Fig. 9) represents a suitable manner for the evaluation of degradation level.

Polymer systems improved by inorganic protectors. Page 14

The co-operation factor, q, describing the sustained contribution of two compounding additives, is an illustrative value for the stabilization activity of certain couple, which presents amounted effects. Defining the contributions of the both couple component, they indicate the degrees of sustainment for the mitigation of oxidation. For the calculation of co-operation factor, the following equation is applied:

 =

where: q is the value of co-operation factor, t₁, t₂ and t_1,2 are the values of the oxidation induction time for component 1, component 2 and couple 1+2.

Conclusion. Page 15

The high quality composite materials become vital supports for the equipments with long term usage, which is intrinsically obtained by inorganic compounds.

Regarding my previous comments, the authors still have not understood that a review is the most exhaustive synthesis as possible of the research works performed by the scientific community on a subject, and not a summary of its own research works. No new bibliographic references have been added to reduce the high number of self-citations (there are more than 20% of citations of papers written by Zaharescu and coll.). I had suggested to the authors to add latest advances in the chemical aspects of stabilization that have been forgotten, but also the physical aspects of stabilization which are no less important. But it is clear that they have no knowledge of these research works, which are however well described in the literature, and that they do not wish to make the effort to take them into consideration. It is really a shame.

Round 2 of comments

Yes, the reviewer has right. This approach is applicable to the largely and deeply investigated research ways. This review wants to provide an alarm sound that the hindered phenols and amines are unhealthy and the consumers are deeply affected by their presence. It is of a great importance the substitution of organic antioxidants with inorganic structures, especially the doped lattices, whose effects are similar with the “classical” stabilizers. The incredible low papers are describing the stabilization effects of the inorganic fillers. The authors prefer to report the improvement of functional properties, by which the reported materials may be successfully used for a certain application (!!!).The publication of Zaharescu’s papers in peer journals proves the interest of scientific world paid to the correlations between the material formulations, the gained resistance and their explanations. It is of a great significance the illustration of the opportunities for the manufacture of ecological products avoiding the step-by step poisoning by phenolic antioxidants. He does not need any advertisement, because he has more than 350 published papers.

Finally, the authors intend to indicate a right direction towards the healthy products, nothing more.

Does the introduction provide sufficient background and include all relevant references?

Yes

The Introduction was improved with severalnew phrases, by which the readers may touch the real sense of paper.

Are all the cited references relevant to the research?

Yes

The authors may firmly sustain that the references are appropriate. If the high proportion of references belong to one author, it means that the treated problem is not found in other papers and the literature in the range has not other alternatives.

Is the research design appropriate?

Yes

The basic idea and the theoretic approach are suitable for a review, because the replacement of organic antioxidants by inorganic structure solves the healthcare problems

Are the conclusions supported by the results?

Yes

The presented conclusions support the necessity of the replacement of organic antioxidants as a pertinent solution for the manufacture of healthy products.

3. Second round of comments

3.1. Lines 40 to 44, what do these two new sentences mean? And above all, what do they bring?

This phrase emphasizes the tight correlation between the physical and structural characteristics and the stabilization activity of the crystalline compounds.

3.2. Lines 96 to 97, it is now stated that “the proportionality between the measured CL intensity and the accumulated amount of peroxyl radicals constitutes the basis for estimating the degradability of polymers”. Knowing that the mechanism responsible for CL is still controversial in the literature and that several kinetic models have been proposed, some of them describing a relationship with the concentration of peroxy radicals but others with the concentration of hydroperoxides, this sentence must be revised.

The oxidative degradation is a complex process started by the reaction of oxygen with free radicals generating peroxyl fragments or the attack of oxygen onto a vulnerable spots of macromolecules generating hydroperoxides. The proportion between the two ways is clearly revealed by the modifications appeared in FTIR spectra in the carbonyl (1720 cm^-1) and hydroperoxyls (~3350 cm^-1) structures. However, the measurements of CL intensities due to the deexcitation of carbonyl structures are generally considered as a reliable proof for the description of degradation progress.

New phrase:

The proportionality between the measured CL intensity and the accumulated amount of peroxyl radicals may be an indication of polymer degradability.

3.3. Lines 205-207, it is now state that “the oxidation induction time (OIT) is the initial stage of degradation, when oxidation progresses so slowly that it can be considered inappropriate to measure”. Knowing that many polymers become brittle and thus reach their lifetime before the end of the induction period, i.e. before the effects of oxidation are detectable by common spectrochemical methods, this sentence needs to be revised.

Well, you are right. When the polymer is deteriorated specially on the outer areas, the oxidation starts earlier from these points. Accordingly, the CL spectra reveal higher values of intensities, because is suddenly detected. In these cases, the oxidation induction times are shortened in respect with the unaged polymer.

3.4. Lines 249 to 252, it is stated that “the carbonyl index, the ratio of the absorbance at 1720 cm-1, the stretching band of carbonyls, to the absorbance at 1460 cm-1 as a reference (Fig. 9), represents a suitable manner for the evaluation of the degradation level”. This is not true at all. Indeed, the band at 1460 cm-1 corresponds to the scissoring vibration of the methylene units in both the amorphous and crystalline phases. However, oxidation also consumes methylene units in EPDM and therefore, choosing the band at 1460 cm-1 as a reference band to assess the progress of oxidation is problematic. In fact, this band is chosen by default because it is not known how to do otherwise. Thus, the sentence needs to be revised accordingly.

The absorbance at 1460 cm-1 may be considered as reference in the spectroscopic investigations. It is a major stretching band whose intensity may be considered constant in its absorbance. We published more than 40 papers, where this band was considered as reference. These papers appeared in several journals like Polymer Degradation and Stability, Polymer, Polymers, Polymer Testing, Materials, Journal of Applied Polymer Science and so on.

Though the absorbance of this band is smoothly changed, it may be considered with certainty as the reference band.

4. Response to Comments on the Quality of English Language

Point 1: Many typos were added to the article during its revision that need to be corrected.

Response 1: We reread carefully the text and made correction, accordingly. All the new corrections are written with red and bold letters.