Special Issue "Processing-Structure-Properties Relationships in Polymers"

A special issue of Polymers (ISSN 2073-4360).

Deadline for manuscript submissions: closed (10 December 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Roberto Pantani

Industrial Engineering Department, University of Salerno, I-84084 Fisciano (Salerno), Italy
Website | E-Mail
Interests: analysis and simulation of injection moulding of thermoplastics; structure development in polymer processing; volume accuracy and stability in polymer processing; processing and degradation of biodegradable polymers

Special Issue Information

Dear Colleagues,

The extraordinary capacity of plastics to modify their properties according to a particular structure could be a difficulty, but also an opportunity, and it is one of the keys to the success of this class of materials.

The same polymer can be transparent or opaque, rigid or flexible, permeable or impermeable, according to the spatial organization of its macromolecules or of a particular filler.

Obviously, the key to taking profit of this peculiar capacity of plastics relies on our capacity of inducing, by means of a suitable processing, that specific spatial organization.

The aim of this Special Issue is to collect a number of research or review papers which can depict the state of the art on the possible correlations between processing variables, obtained structure and the special property, which this structure induces on the plastic part. We would welcome contributions dealing with the related research fields, and I do hope that this stimulating subject will induce you to submit a manuscript to this Special Issue.

Prof. Dr. Roberto Pantani
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • effect of polymer processing on resulting morphology and/or properties
  • mechanical, optical, thermal, transport properties of polymers induced by particular processing conditions and their relationship with the structure
  • composite or nano-composites or in general multiphase polymeric materials with special properties induced by processing

Published Papers (25 papers)

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Research

Open AccessArticle
Structure-Properties Relations for Polyamide 6, Part 2: Influence of Processing Conditions during Injection Moulding on Deformation and Failure Kinetics
Polymers 2018, 10(7), 779; https://doi.org/10.3390/polym10070779
Received: 30 May 2018 / Revised: 7 July 2018 / Accepted: 11 July 2018 / Published: 16 July 2018
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Abstract
The effect of processing conditions during injection on the structure formation and mechanical properties of injection molded polyamide 6 samples was investigated in detail. A large effect of the mold temperature on the crystallographic properties was observed. Also the the effect of pressure [...] Read more.
The effect of processing conditions during injection on the structure formation and mechanical properties of injection molded polyamide 6 samples was investigated in detail. A large effect of the mold temperature on the crystallographic properties was observed. Also the the effect of pressure and shear flow was taken in to consideration and analysed. The yield and failure kinetics, including time-to-failure, were studied by performing tensile and creep tests at several test temperatures and relative humidities. As far as mechanical properties are concerned, a strong influence of temperature and relative humidity on the yield stress and time-to-failure was found. A semi-empirical model, able to describe yield and failure kinetics, was applied to the experimental results and related to the crystalline phase present in the sample. In agreement with findings in the literature it is observed that for high mold temperatures the sample morphology is more stable with respect to humidity and temperature than in case of low mold temperatures and this effects could be successfully captured by the model. The samples molded at low temperatures showed, during mechanical testing, a strong evolution of the crystallographic properties when exposed to high testing temperature and high relative humidity, i.e., an increase of crystallinity or a crystal phase transition. This makes a full description of the mechanical behavior rather complicated. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Structure–Properties Relations for Polyamide 6, Part 1: Influence of the Thermal History during Compression Moulding on Deformation and Failure Kinetics
Polymers 2018, 10(7), 710; https://doi.org/10.3390/polym10070710
Received: 30 May 2018 / Accepted: 20 June 2018 / Published: 27 June 2018
Cited by 1 | PDF Full-text (1027 KB) | HTML Full-text | XML Full-text
Abstract
The deformation and failure kinetics of polyamide 6 samples prepared by several thermal histories were investigated by tests at different temperatures and relative humidities. PA6 samples were produced in quiescent condition and multiple cooling procedure. A characterization was performed to investigate the effect [...] Read more.
The deformation and failure kinetics of polyamide 6 samples prepared by several thermal histories were investigated by tests at different temperatures and relative humidities. PA6 samples were produced in quiescent condition and multiple cooling procedure. A characterization was performed to investigate the effect of the different thermal histories and the effect of hydration on both structures and glass transition temperature. The mechanical properties were investigated by tensile and creep tests at different temperatures and relative humidity. In order to describe the experimental results, the Ree–Eyring equation, modified with the “apparent temperature”, was employed. In addition, the results of time-to-failure (creep tests) were described by the use of the “critical strain” concept. Eventually, a link between the Eyring theory and the structure evolution was made, i.e., a relation between the rate factors and the average lamellar thickness. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Processing and Thermal Response of Temperature-Sensitive-Gel(TSG)/Polymer Composites
Polymers 2018, 10(5), 486; https://doi.org/10.3390/polym10050486
Received: 4 April 2018 / Revised: 26 April 2018 / Accepted: 28 April 2018 / Published: 1 May 2018
Cited by 1 | PDF Full-text (5747 KB) | HTML Full-text | XML Full-text
Abstract
Temperature-sensitive gels (TSGs) are generally used in the fields of medical, robotics, MEMS, and also in daily life. In this paper, we synthesized a novel TSG with good thermal durability and a lower melting temperature below 60 °C. We discussed the physical properties [...] Read more.
Temperature-sensitive gels (TSGs) are generally used in the fields of medical, robotics, MEMS, and also in daily life. In this paper, we synthesized a novel TSG with good thermal durability and a lower melting temperature below 60 °C. We discussed the physical properties of he TSG and found it provided excellent thermal expansion. Therefore, we proposed the usage of TSG to develop a strategic breathable film with controllable gas permeability. The TSG particles were prepared firstly and then blended with linear low-density polyethylene/calcium carbonate (LLDPE/CaCO3) composite to develop microporous TSG/LLDPE/CaCO3 films. We investigated the morphology, thermal, and mechanical properties of TSG/LLDPE/CaCO3 composite films. The film characterization was conducted by gas permeability testing and demonstration temperature control experiments. The uniformly porous structure and the pore size in the range of 5–40 μm for the TSG/LLDPE/CaCO3 composite films were indicated by SEM micrographs. The demonstration temperature control experiments clearly proved the effect of the controllable gas permeability of the TSG and, more promisingly, the great practical value and application prospects of this strategic effect for the temperature-sensitive breathable film was proved. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Single-Point Incremental Forming of Two Biocompatible Polymers: An Insight into Their Thermal and Structural Properties
Polymers 2018, 10(4), 391; https://doi.org/10.3390/polym10040391
Received: 6 March 2018 / Revised: 20 March 2018 / Accepted: 28 March 2018 / Published: 1 April 2018
Cited by 3 | PDF Full-text (15543 KB) | HTML Full-text | XML Full-text
Abstract
Sheets of polycaprolactone (PCL) and ultra-high molecular weight polyethylene (UHMWPE) were fabricated and shaped by the Single-Point Incremental Forming process (SPIF). The performance of these biocompatible polymers in SPIF was assessed through the variation of four main parameters: the diameter of the forming [...] Read more.
Sheets of polycaprolactone (PCL) and ultra-high molecular weight polyethylene (UHMWPE) were fabricated and shaped by the Single-Point Incremental Forming process (SPIF). The performance of these biocompatible polymers in SPIF was assessed through the variation of four main parameters: the diameter of the forming tool, the spindle speed, the feed rate, and the step size based on a Box–Behnken design of experiments of four variables and three levels. The design of experiments allowed us to identify the parameters that most affect the forming of PCL and UHMWPE. The study was completed by means of a deep characterization of the thermal and structural properties of both polymers. These properties were correlated to the performance of the polymers observed in SPIF, and it was found that the polymer chains are oriented as a consequence of the SPIF processing. Moreover, by X-ray diffraction it was proved that polymer chains behave differently on each surface of the fabricated parts, since the chains on the surface in contact with the forming tool are oriented horizontally, while on the opposite surface they are oriented in the vertical direction. The unit cell of UHMWPE is distorted, passing from an orthorhombic cell to a monoclinic due to the slippage between crystallites. This slippage between crystallites was observed in both PCL and UHMWPE, and was identified as an alpha star thermal transition located in the rubbery region between the glass transition and the melting point of each polymer. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Hydrophobicity Tuning by the Fast Evolution of Mold Temperature during Injection Molding
Polymers 2018, 10(3), 322; https://doi.org/10.3390/polym10030322
Received: 2 February 2018 / Revised: 26 February 2018 / Accepted: 9 March 2018 / Published: 15 March 2018
Cited by 3 | PDF Full-text (4402 KB) | HTML Full-text | XML Full-text
Abstract
The surface topography of a molded part strongly affects its functional properties, such as hydrophobicity, cleaning capabilities, adhesion, biological defense and frictional resistance. In this paper, the possibility to tune and increase the hydrophobicity of a molded polymeric part was explored. An isotactic [...] Read more.
The surface topography of a molded part strongly affects its functional properties, such as hydrophobicity, cleaning capabilities, adhesion, biological defense and frictional resistance. In this paper, the possibility to tune and increase the hydrophobicity of a molded polymeric part was explored. An isotactic polypropylene was injection molded with fast cavity surface temperature evolutions, obtained adopting a specifically designed heating system layered below the cavity surface. The surface topology was characterized by atomic force microscopy (AFM) and, concerning of hydrophobicity, by measuring the water static contact angle. Results show that the hydrophobicity increases with both the temperature level and the time the cavity surface temperature was kept high. In particular, the contact angle of the molded sample was found to increase from 90°, with conventional molding conditions, up to 113° with 160 °C of cavity surface temperature kept for 18 s. This increase was found to be due to the presence of sub-micro and nano-structures characterized by high values of spatial frequencies which could be more accurately replicated by adopting high heating temperatures and times. The surface topography and the hydrophobicity resulted therefore tunable by selecting appropriate injection molding conditions. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Orthogonal Templating Control of the Crystallisation of Poly(ε-Caprolactone)
Polymers 2018, 10(3), 300; https://doi.org/10.3390/polym10030300
Received: 8 January 2018 / Revised: 27 February 2018 / Accepted: 2 March 2018 / Published: 11 March 2018
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Abstract
The crystal growth of poly(ε-caprolactone) can be very effectively directed through the use of small amounts of dibenzylidene sorbitol in conjunction with modest flow fields to yield extremely high levels of the preferred polymer crystal orientation. We show that by introducing small quantities [...] Read more.
The crystal growth of poly(ε-caprolactone) can be very effectively directed through the use of small amounts of dibenzylidene sorbitol in conjunction with modest flow fields to yield extremely high levels of the preferred polymer crystal orientation. We show that by introducing small quantities of a terpolymer, based on polyvinyl butyral we can switch the symmetry axis of the final lamellar orientation from parallel to perpendicular to the melt flow direction. During shear flow of the polymer melt, the dibenzylidene sorbitol forms highly extended nanoparticles which adopt a preferred alignment with respect to the flow field and on cooling, polymer crystallisation is directed by these particles. The presence of the terpolymer, based on polyvinyl butyral, limits the aspect ratio of the dibenzylidene sorbitol (DBS) particles, such that the preferred orientation of the particles in the polymer melt changes from parallel to normal to the flow direction. The alignment of lamellar crystals perpendicular to the flow direction has important implications for applications such as scaffolds for tissue engineering and for barrier film properties. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Development of Crystalline Morphology and Its Relationship with Mechanical Properties of PP/PET Microfibrillar Composites Containing POE and POE-g-MA
Polymers 2018, 10(3), 291; https://doi.org/10.3390/polym10030291
Received: 9 February 2018 / Revised: 2 March 2018 / Accepted: 5 March 2018 / Published: 8 March 2018
Cited by 5 | PDF Full-text (7666 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in [...] Read more.
The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in two different steps in the processing sequence. The MFCs were prepared at a weight ratio of 80/20 PP/PET by twin screw extrusion followed by cold drawing and injection moulding. The non-functionalized polyolefin-based elastomer (POE) and the functional compatibilizer (i.e., POE grafted with maleic anhydride (POE-g-MA)) were added in a fixed weight percentage at two stages: during extrusion or during injection moulding. The morphology observations showed differences in crystalline structure, and the PP spherulite size was reduced in all MFCs due to the presence of PET fibrils. Their relationship with the mechanical performances of the composite was studied by tensile and impact tests. Adding the functional compatibilizer during extrusions showed better mechanical properties compared to MFCs. Overall, a clear relationship was identified between processing, structure and properties. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Tube Expansion Deformation Enables In Situ Synchrotron X-ray Scattering Measurements during Extensional Flow-Induced Crystallization of Poly l-Lactide Near the Glass Transition
Polymers 2018, 10(3), 288; https://doi.org/10.3390/polym10030288
Received: 11 February 2018 / Revised: 4 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
Cited by 2 | PDF Full-text (6257 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable [...] Read more.
Coronary Heart Disease (CHD) is one of the leading causes of death worldwide, claiming over seven million lives each year. Permanent metal stents, the current standard of care for CHD, inhibit arterial vasomotion and induce serious complications such as late stent thrombosis. Bioresorbable vascular scaffolds (BVSs) made from poly l-lactide (PLLA) overcome these complications by supporting the occluded artery for 3–6 months and then being completely resorbed in 2–3 years, leaving behind a healthy artery. The BVS that recently received clinical approval is, however, relatively thick (~150 µm, approximately twice as thick as metal stents ~80 µm). Thinner scaffolds would facilitate implantation and enable treatment of smaller arteries. The key to a thinner scaffold is careful control of the PLLA microstructure during processing to confer greater strength in a thinner profile. However, the rapid time scales of processing (~1 s) defy prediction due to a lack of structural information. Here, we present a custom-designed instrument that connects the strain-field imposed on PLLA during processing to in situ development of microstructure observed using synchrotron X-ray scattering. The connection between deformation, structure and strength enables processing–structure–property relationships to guide the design of thinner yet stronger BVSs. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Modelling of Rod-Like Fillers’ Rotation and Translation near Two Growing Cells in Conductive Polymer Composite Foam Processing
Polymers 2018, 10(3), 261; https://doi.org/10.3390/polym10030261
Received: 11 January 2018 / Revised: 14 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
Cited by 4 | PDF Full-text (2858 KB) | HTML Full-text | XML Full-text
Abstract
We developed a simple analytical model to describe the instantaneous location and angle of rod-like conductive fillers as a function of cell growth during the foaming of conductive polymer composites (CPCs). First, we modelled the motion of the fillers that resulted from the [...] Read more.
We developed a simple analytical model to describe the instantaneous location and angle of rod-like conductive fillers as a function of cell growth during the foaming of conductive polymer composites (CPCs). First, we modelled the motion of the fillers that resulted from the growth of one cell. Then, by taking into account the fillers located at the line that connected the centres of the two growing cells, we found the final filler’s angle and location. We identified this as a function of the corresponding cell size, filler size, and the filler’s initial angle and location. We based the model’s development on the assumption that a polymer melt is incompressible during cell growth. The two-cell growth model is better than the one-cell growth model because it describes the filler’s movement in the cell wall between the two growing cells. The results revealed that the fillers near the cell were the ones most affected by the cell growth, while those at the midpoint between the two cells were the least affected. As a cell grows, its affected polymer area also increases. A dimensionless factor η was introduced to demonstrate the effects of the cell size and the filler length on the filler’s interconnectivity in the CPC foams. It is vital to keep the filler length comparable to the cell size when preparing CPC foams with the desired electrical conductivity. Our research provides a deeper understanding of the mechanism through which foaming influences the filler connections in CPC foams. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Effect of Polyhedral Oligomeric Silsesquioxane on the Melting, Structure, and Mechanical Behavior of Polyoxymethylene
Polymers 2018, 10(2), 203; https://doi.org/10.3390/polym10020203
Received: 8 December 2017 / Revised: 13 February 2018 / Accepted: 14 February 2018 / Published: 17 February 2018
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Abstract
The effects of octakis[(3-glycidoxypropyl)dimethylsiloxy]octasilsesquioxane (GPOSS) on the crystallinity, crystal structure, morphology, and mechanical properties of polyoxymethylene (POM) and POM/GPOSS composites were investigated. The POM/GPOSS composites with varying concentrations of GPOSS nanoparticles (0.05–0.25 wt %) were prepared via melt blending. The structure of POM/GPOSS [...] Read more.
The effects of octakis[(3-glycidoxypropyl)dimethylsiloxy]octasilsesquioxane (GPOSS) on the crystallinity, crystal structure, morphology, and mechanical properties of polyoxymethylene (POM) and POM/GPOSS composites were investigated. The POM/GPOSS composites with varying concentrations of GPOSS nanoparticles (0.05–0.25 wt %) were prepared via melt blending. The structure of POM/GPOSS composites was characterized by differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized light microscopy (PLM). The mechanical properties were determined by standardized tensile tests. The morphology and dispersion of GPOSS nanoparticles in the POM matrix were investigated with scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was observed that the dispersion of the GPOSS nanoparticles was uniform. Based on DSC studies, it was found that the melting temperature, lamellar thickness, and the degree of crystallinity of the POM/GPOSS composites increased. The POM/GPOSS composites showed an increased Young’s modulus and tensile strength. Finally, compared with the pure POM, the addition of GPOSS reduced the spherulites’ size and improved the crystallinity of the POM, which demonstrates that the nucleation effect of GPOSS is favorable for the mechanical properties of POM. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Time-Resolving Study of Stress-Induced Transformations of Isotactic Polypropylene through Wide Angle X-ray Scattering Measurements
Polymers 2018, 10(2), 162; https://doi.org/10.3390/polym10020162
Received: 3 January 2018 / Revised: 5 February 2018 / Accepted: 6 February 2018 / Published: 8 February 2018
Cited by 3 | PDF Full-text (9480 KB) | HTML Full-text | XML Full-text
Abstract
The development of a highly oriented fiber morphology by effect of tensile deformation of stereodefective isotactic polypropylene (iPP) samples, starting from the unoriented γ form, is studied by following the transformation in real time during stretching through wide angle X-ray scattering (WAXS) measurements. [...] Read more.
The development of a highly oriented fiber morphology by effect of tensile deformation of stereodefective isotactic polypropylene (iPP) samples, starting from the unoriented γ form, is studied by following the transformation in real time during stretching through wide angle X-ray scattering (WAXS) measurements. In the stretching process, after yielding, the initial γ form transforms into the mesomorphic form of iPP through mechanical melting and re-crystallization. The analysis of the scattering invariant measured in the WAXS region highlights that the size of the mesomorphic domains included in the well oriented fiber morphology obtained at high deformations increases through a process which involves the coalescence of the small fragments formed by effect of tensile stress during lamellar destruction with the domain of higher dimensions. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
An Investigation and Comparison of the Blending of LDPE and PP with Different Intrinsic Viscosities of PET
Polymers 2018, 10(2), 147; https://doi.org/10.3390/polym10020147
Received: 5 December 2017 / Revised: 1 February 2018 / Accepted: 1 February 2018 / Published: 5 February 2018
Cited by 4 | PDF Full-text (4610 KB) | HTML Full-text | XML Full-text
Abstract
The blending of aliphatic polyolefins and aromatic poly(ethylene terephthalate) (PET) based on different intrinsic viscosities (IV) was conducted in a torque rheometer. The comparison of blend components in terms of low density polythene (LDPE) and polypropylene (PP) in blending with PET was investigated, [...] Read more.
The blending of aliphatic polyolefins and aromatic poly(ethylene terephthalate) (PET) based on different intrinsic viscosities (IV) was conducted in a torque rheometer. The comparison of blend components in terms of low density polythene (LDPE) and polypropylene (PP) in blending with PET was investigated, and the effects of the IV and proportion of PET on polymer blends are discussed in detail. Polymer blends with or without compatibilizer were examined by using a differential scanning calorimeter, thermogravimetric analyzer, rotary rheometer, field-emission scanning electron microscopy and a universal testing machine. It was found that the blending led to an increase in processability and a decrease in thermal stability for blends. The morphological analysis revealed that the incompatibility of blends was aggravated by a higher IV of PET, while this situation could be improved by the addition of compatibilizer. Results showed that there was an opposite effect for the tensile strength and the elongation at break of the polymer blend in the presence of a compatibilizer, wherein the influence of IV of PET was complicated. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
PLA Melt Stabilization by High-Surface-Area Graphite and Carbon Black
Polymers 2018, 10(2), 139; https://doi.org/10.3390/polym10020139
Received: 31 December 2017 / Revised: 24 January 2018 / Accepted: 30 January 2018 / Published: 1 February 2018
Cited by 4 | PDF Full-text (2321 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Small amounts of carbon nanofillers, specifically high-surface-area graphite (HSAG) and more effectively carbon black (CB), are able to solve the well-known problem of degradation (molecular weight reduction) during melt processing, for the most relevant biodegradable polymer, namely poly(lactic acid), PLA. This behavior is [...] Read more.
Small amounts of carbon nanofillers, specifically high-surface-area graphite (HSAG) and more effectively carbon black (CB), are able to solve the well-known problem of degradation (molecular weight reduction) during melt processing, for the most relevant biodegradable polymer, namely poly(lactic acid), PLA. This behavior is shown by rheological measurements (melt viscosity during extrusion experiments and time sweep-complex viscosity) combined with gel permeation chromatography (GPC) experiments. PLA’s molecular weight, which is heavily reduced during melt extrusion of the neat polymer, can remain essentially unaltered by simple compounding with only 0.1 wt % of CB. At temperatures close to polymer melting by compounding with graphitic fillers, the observed stabilization of PLA melt could be rationalized by scavenging traces of water, which reduces hydrolysis of polyester bonds. Thermogravimetric analyses (TGA) indicate that the same carbon fillers, on the contrary, slightly destabilize PLA toward decomposition reactions, leading to the loss of volatile byproducts, which occur at temperatures higher than 300 °C, i.e., far from melt processing conditions. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Effect of Curing Rate on the Microstructure and Macroscopic Properties of Epoxy Fiberglass Composites
Polymers 2018, 10(2), 125; https://doi.org/10.3390/polym10020125
Received: 11 December 2017 / Revised: 21 January 2018 / Accepted: 24 January 2018 / Published: 27 January 2018
Cited by 2 | PDF Full-text (2568 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Curing rates of an epoxy amine system were varied via different curing cycles, and glass-fiber epoxy composites were prepared using the same protocol, with the aim of investigating the correlation between microstructure and composite properties. It was found that the fast curing cycle [...] Read more.
Curing rates of an epoxy amine system were varied via different curing cycles, and glass-fiber epoxy composites were prepared using the same protocol, with the aim of investigating the correlation between microstructure and composite properties. It was found that the fast curing cycle resulted in a non-homogenous network, with a larger percentage of a softer phase. Homogenized composite properties, namely storage modulus and quasi-static intra-laminar shear strength, remained unaffected by the change in resin microstructure. However, fatigue tests revealed a significant reduction in fatigue life for composites cured at fast curing rates, while composites with curing cycles that allowed a pre-cure until the critical gel point, were unaffected by the rate of reaction. This result was explained by the increased role of epoxy microstructure on damage initiation and propagation in the matrix during fatigue life. Therefore, local non-homogeneities in the epoxy matrix, corresponding to regions with variable crosslink density, can play a significant role in limiting the fatigue life of composites and must be considered in the manufacturing of large scale components, where temperature gradients and significant exotherms are expected. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Toughening of Poly(lactic acid) and Thermoplastic Cassava Starch Reactive Blends Using Graphene Nanoplatelets
Polymers 2018, 10(1), 95; https://doi.org/10.3390/polym10010095
Received: 21 November 2017 / Revised: 12 January 2018 / Accepted: 15 January 2018 / Published: 19 January 2018
Cited by 14 | PDF Full-text (2687 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Poly(lactic acid) (PLA) was reactively blended with thermoplastic cassava starch (TPCS) and functionalized with commercial graphene (GRH) nanoplatelets in a twin-screw extruder, and films were produced by cast-film extrusion. Reactive compatibilization between PLA and TPCS phases was reached by introducing maleic anhydride and [...] Read more.
Poly(lactic acid) (PLA) was reactively blended with thermoplastic cassava starch (TPCS) and functionalized with commercial graphene (GRH) nanoplatelets in a twin-screw extruder, and films were produced by cast-film extrusion. Reactive compatibilization between PLA and TPCS phases was reached by introducing maleic anhydride and a peroxide radical during the reactive blending extrusion process. Films with improved elongation at break and toughness for neat PLA and PLA-g-TPCS reactive blends were obtained by an addition of GRH nanoplatelets. Toughness of the PLA-g-TPCS-GRH was improved by ~900% and ~500% when compared to neat PLA and PLA-g-TPCS, respectively. Crack bridging was established as the primary mechanism responsible for the improvement in the mechanical properties of PLA and PLA-g-TPCS in the presence of the nanofiller due to the high aspect ratio of GRH. Scanning electron microscopy images showed a non-uniform distribution of GRH nanoplatelets in the matrix. Transmittance of the reactive blend films decreased due to the TPCS phase. Values obtained for the reactive blends showed ~20% transmittance. PLA-GRH and PLA-g-TPCS-GRH showed a reduction of the oxygen permeability coefficient with respect to PLA of around 35% and 50%, respectively. Thermal properties, molecular structure, surface roughness, XRD pattern, electrical resistivity, and color of the films were also evaluated. Biobased and compostable reactive blend films of PLA-g-TPCS compounded with GRH nanoplatelets could be suitable for food packaging and agricultural applications. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Ionic Liquid as Surfactant Agent of Hydrotalcite: Influence on the Final Properties of Polycaprolactone Matrix
Polymers 2018, 10(1), 44; https://doi.org/10.3390/polym10010044
Received: 30 October 2017 / Revised: 15 December 2017 / Accepted: 29 December 2017 / Published: 5 January 2018
Cited by 5 | PDF Full-text (2545 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports the surface treatment of layered double hydroxide (LDH) by using ionic liquid (IL) composed of phosphonium cation combined with 2-ethylhexanoate (EHT) counter anion as surfactant agent. Then, different amounts (1, 3, 5 and 7 wt %) of thermally stable organically [...] Read more.
This paper reports the surface treatment of layered double hydroxide (LDH) by using ionic liquid (IL) composed of phosphonium cation combined with 2-ethylhexanoate (EHT) counter anion as surfactant agent. Then, different amounts (1, 3, 5 and 7 wt %) of thermally stable organically modified LDH (up to 350 °C) denoted LDH-EHT were incorporated into polycaprolactone (PCL) matrix by mechanical milling. The influence of LDH-EHT loading has been investigated on the physical properties, such as the thermal and barrier properties, as well as the morphologies of the resulting nanocomposites. Thus, intercalated or microcomposite morphologies were obtained depending on the LDH-EHT loading, leading to significant reduction of the diffusion coefficient respect to water vapor. The modulation of barrier properties, using low functionalized filler amount, is a very important aspect for materials in packaging applications. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Independent Evaluation of Medical-Grade Bioresorbable Filaments for Fused Deposition Modelling/Fused Filament Fabrication of Tissue Engineered Constructs
Polymers 2018, 10(1), 40; https://doi.org/10.3390/polym10010040
Received: 9 December 2017 / Revised: 29 December 2017 / Accepted: 31 December 2017 / Published: 2 January 2018
Cited by 6 | PDF Full-text (5430 KB) | HTML Full-text | XML Full-text
Abstract
Three-dimensional printing/additive manufacturing (3DP/AM) for tissue engineering and regenerative medicine (TE/RM) applications is a multifaceted research area encompassing biology, material science, engineering, and the clinical sciences. Although being quite mature as a research area, only a handful of clinical cases have been reported [...] Read more.
Three-dimensional printing/additive manufacturing (3DP/AM) for tissue engineering and regenerative medicine (TE/RM) applications is a multifaceted research area encompassing biology, material science, engineering, and the clinical sciences. Although being quite mature as a research area, only a handful of clinical cases have been reported and even fewer commercial products have made it to the market. The regulatory pathway and costs associated with the introduction of bioresorbable materials for TE/RM have proven difficult to overcome, but greater access to 3DP/AM has spurred interest in the processing and availability of existing and new bioresorbable materials. For this purpose, herein, we introduce a series of medical-grade filaments for fused deposition modelling/fused filament fabrication (FDM/FFF) based on established and Federal Drug Administration (FDA)-approved polymers. Manufacturability, mechanical characterization, and accelerated degradation studies have been conducted to evaluate the suitability of each material for TE/RM applications. The comparative data serves to introduce these materials, as well as a benchmark to evaluate their potential in hard and soft tissue engineering from a physicochemical perspective. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Improved Processability and the Processing-Structure-Properties Relationship of Ultra-High Molecular Weight Polyethylene via Supercritical Nitrogen and Carbon Dioxide in Injection Molding
Polymers 2018, 10(1), 36; https://doi.org/10.3390/polym10010036
Received: 8 December 2017 / Revised: 27 December 2017 / Accepted: 28 December 2017 / Published: 30 December 2017
Cited by 6 | PDF Full-text (1899 KB) | HTML Full-text | XML Full-text
Abstract
The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN2) or supercritical carbon dioxide (scCO2) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. [...] Read more.
The processability of injection molding ultra-high molecular weight polyethylene (UHMWPE) was improved by introducing supercritical nitrogen (scN2) or supercritical carbon dioxide (scCO2) into the polymer melt, which decreased its viscosity and injection pressure while reducing the risk of degradation. When using the special full-shot option of microcellular injection molding (MIM), it was found that the required injection pressure decreased by up to 30% and 35% when scCO2 and scN2 were used, respectively. The mechanical properties in terms of tensile strength, Young’s modulus, and elongation-at-break of the supercritical fluid (SCF)-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. The results showed that the temperature dependence of UHMWPE was very low, suggesting that increasing the processing temperature is not a viable method for reducing injection pressure or improving processability. Moreover, the use of scN2 and scCO2 with UHMWPE and MIM retained the high molecular weight, and thus the mechanical properties, of the polymer, while regular injection molding led to signs of degradation. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Effect of Cross-Linking on the Performances of Starch-Based Biopolymer as Gel Electrolyte for Dye-Sensitized Solar Cell Applications
Polymers 2017, 9(12), 667; https://doi.org/10.3390/polym9120667
Received: 19 October 2017 / Revised: 28 November 2017 / Accepted: 29 November 2017 / Published: 1 December 2017
Cited by 5 | PDF Full-text (3184 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Dye-sensitized solar cells (DSSCs) have become a validated and economically credible competitor to the traditional solid-state junction photovoltaic devices. DSSCs based on biopolymer gel electrolyte systems offer the perspective of competitive conversion efficiencies with a very low-cost fabrication. In this paper, a new [...] Read more.
Dye-sensitized solar cells (DSSCs) have become a validated and economically credible competitor to the traditional solid-state junction photovoltaic devices. DSSCs based on biopolymer gel electrolyte systems offer the perspective of competitive conversion efficiencies with a very low-cost fabrication. In this paper, a new starch-based biopolymer gel electrolyte system is prepared by mixing lithium iodide and iodine with bare and citric acid cross-linked potato starches with glycerol as the plasticizing agent. The effect of the preparation methods on the starch cross-linking degree as well as the photoconversion efficiency of the resulting DSSC cells is carefully analyzed. Fourier transform spectroscopy, X-ray diffraction, and scanning electron microscopy were used to characterize the morphology and conformational changes of starch in the electrolytes. The conductivity of the biopolymer electrolytes was determined by electrochemical impedance spectroscopy. DSSC based on the starch-gel polymer electrolytes were characterized by photovoltaic measurements and electrochemical impedance spectroscopy. Results clearly show that the cross-linking increases the recombination resistance and open circuit voltage (VOC) of the DSSC, and thereby the photoconversion efficiency of the cell. In particular, electrolytes containing 1.4 g bare and cross-linked starches showed ionic conductivities of σ = 1.61, 0.59, 0.38, and 0.35 S cm−1, and the corresponding DSSCs showed efficiencies of 1.2, 1.4, 0.93, and 1.11%, respectively. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Mechanical Properties Distribution within Polypropylene Injection Molded Samples: Effect of Mold Temperature under Uneven Thermal Conditions
Polymers 2017, 9(11), 585; https://doi.org/10.3390/polym9110585
Received: 13 October 2017 / Revised: 1 November 2017 / Accepted: 3 November 2017 / Published: 7 November 2017
Cited by 6 | PDF Full-text (6905 KB) | HTML Full-text | XML Full-text
Abstract
The quality of the polymer parts produced by injection molding is strongly affected by the processing conditions. Uncontrolled deviations from the proper process parameters could significantly affect both internal structure and final material properties. In this work, to mimic an uneven temperature field, [...] Read more.
The quality of the polymer parts produced by injection molding is strongly affected by the processing conditions. Uncontrolled deviations from the proper process parameters could significantly affect both internal structure and final material properties. In this work, to mimic an uneven temperature field, a strong asymmetric heating is applied during the production of injection-molded polypropylene samples. The morphology of the samples is characterized by optical and atomic force microscopy (AFM), whereas the distribution of mechanical modulus at different scales is obtained by Indentation and HarmoniX AFM tests. Results clearly show that the temperature differences between the two mold surfaces significantly affect the morphology distributions of the molded parts. This is due to both the uneven temperature field evolutions and to the asymmetric flow field. The final mechanical property distributions are determined by competition between the local molecular stretch and the local structuring achieved during solidification. The cooling rate changes affect internal structures in terms of relaxation/reorganization levels and give rise to an asymmetric distribution of mechanical properties. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Deformation-Induced Phase Transitions in iPP Polymorphs
Polymers 2017, 9(10), 547; https://doi.org/10.3390/polym9100547
Received: 21 August 2017 / Revised: 28 September 2017 / Accepted: 18 October 2017 / Published: 24 October 2017
Cited by 9 | PDF Full-text (19702 KB) | HTML Full-text | XML Full-text
Abstract
This detailed study reveals the relation between structural evolution and the mechanical response of α-, β- and γ-iPP. Uni-axial compression experiments, combined with in situ WAXD measurements, allowed for the identification of the evolution phenomena in terms of phase composition. [...] Read more.
This detailed study reveals the relation between structural evolution and the mechanical response of α -, β - and γ -iPP. Uni-axial compression experiments, combined with in situ WAXD measurements, allowed for the identification of the evolution phenomena in terms of phase composition. Tensile experiments in combination with SAXS revealed orientation and voiding phenomena, as well as structural evolution in the thickness of the lamellae and amorphous layers. On the level of the crystallographic unit cell, the WAXD experiments provided insight into the early stages of deformation. Moreover, transitions in the crystal phases taking place in the larger deformation range and the orientation of crystal planes were monitored. At all stretching temperatures, the crystallinity decreases upon deformation, and depending on the temperature, different new structures are formed. Stretching at low temperatures leads to crystal destruction and the formation of the oriented mesophase, independent of the initial polymorph. At high temperatures, above T α c , all polymorphs transform into oriented α -iPP. Small quantities of the initial structures remain present in the material. The compression experiments, where localization phenomena are excluded, show that these transformations take place at similar strains for all polymorphs. For the post yield response, the strain hardening modulus is decisive for the mechanical behavior, as well as for the orientation of lamellae and the evolution of void fraction and dimensions. β -iPP shows by far the most intense voiding in the entire experimental temperature range. The macroscopic localization behavior and strain at which the transition from disk-like void shapes, oriented with the normal in tensile direction, into fibrillar structures takes place is directly correlated with the strain hardening modulus. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Mixed Rigid and Flexible Component Design for High-Performance Polyimide Films
Polymers 2017, 9(9), 451; https://doi.org/10.3390/polym9090451
Received: 25 July 2017 / Revised: 11 September 2017 / Accepted: 14 September 2017 / Published: 15 September 2017
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Abstract
To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and [...] Read more.
To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and thermal imidization process. The physical properties of the PIs are effectively regulated and optimized by adjusting the ratio of the rigid DAPBI and flexible ODA components. By increasing the DAPBI content, thermal stability, dimensional stability, and mechanical properties, the resultant polymer is enhanced. PI-80 exhibits an excellent comprehensive performance, a glass transition temperature of 370 °C, and a tensile strength of 210 MPa. Furthermore, the CTE as calculated in the range 50–250 °C is ca. 19 ppm/K, which is equal to that of copper. A highly dimensionally stable, curl-free, and high T-style peel strength (6.4 N/cm) of copper/PI laminate was obtained by casting the polyamic acid onto copper foil (13 μm) and thermally curing at 360 °C, which indicates that it has the potential to be applied as an electronic film for flexible displays and flexible printed circuit boards. A structural rationalization for these remarkable properties is also presented. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Fabrication of Multi-Layered Lidocaine and Epinephrine-Eluting PLGA/Collagen Nanofibers: In Vitro and In Vivo Study
Polymers 2017, 9(9), 416; https://doi.org/10.3390/polym9090416
Received: 9 August 2017 / Revised: 30 August 2017 / Accepted: 3 September 2017 / Published: 5 September 2017
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Abstract
This study developed multi-layered lidocaine- and epinephrine-eluting biodegradable poly[(d,l)-lactide-co-glyco lide] (PLGA)/collagen nanofibers. An electrospinning technique was employed to fabricate the multi-layer biodegradable drug-eluting nanofibers. After fabrication, the nanofibrous membranes were characterized. The drug release characteristics were also investigated. In [...] Read more.
This study developed multi-layered lidocaine- and epinephrine-eluting biodegradable poly[(d,l)-lactide-co-glyco lide] (PLGA)/collagen nanofibers. An electrospinning technique was employed to fabricate the multi-layer biodegradable drug-eluting nanofibers. After fabrication, the nanofibrous membranes were characterized. The drug release characteristics were also investigated. In addition, the in vivo efficacy of nanofibers for pain relief and hemostasis in palatal oral wounds of rabbits were evaluated. Histological examinations were also completed. The experimental results suggested that all nanofibers exhibited good biocompatibility and eluted effective levels of lidocaine and epinephrine at the initial stages of wound recovery. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Preparation and Flame Retardance of Polyurethane Composites Containing Microencapsulated Melamine Polyphosphate
Polymers 2017, 9(9), 407; https://doi.org/10.3390/polym9090407
Received: 13 July 2017 / Revised: 21 August 2017 / Accepted: 29 August 2017 / Published: 31 August 2017
Cited by 4 | PDF Full-text (5078 KB) | HTML Full-text | XML Full-text
Abstract
A new microencapsulated flame retardant containing melamine polyphosphate (MPP) and 4,4′-oxydianiline-formaldehyde (OF) resin as the core and shell materials, respectively, was synthesized by in situ polymerization. 29Si NMR was used to measure the condensation density of polyurethane containing silicon compound (Si-PU). The [...] Read more.
A new microencapsulated flame retardant containing melamine polyphosphate (MPP) and 4,4′-oxydianiline-formaldehyde (OF) resin as the core and shell materials, respectively, was synthesized by in situ polymerization. 29Si NMR was used to measure the condensation density of polyurethane containing silicon compound (Si-PU). The structures and properties of the microencapsulated melamine polyphosphate (OFMPP) were characterized using X-ray photoelectron spectroscopy, scanning electron microscopy and water solubility. Thermal behavior of the OFMPP was systematically analyzed through thermogravimetric analysis. Flame retardance tests such as the limiting oxygen index and UL-94 were employed to evaluate the effect of composition variation on the MPP and OFMPP in polyurethane composites. The results indicated that the microencapsulation of MPP with the OF resin improved hydrophobicity and that the flame retardance of the Si-PU/OFMPP composite (limiting oxygen index, LOI = 32%) was higher than that of the Si-PU/MPP composite (LOI = 27%) at the same additive loading (30 wt %). Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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Open AccessArticle
Octadecylamine-Grafted Graphene Oxide Helps the Dispersion of Carbon Nanotubes in Ethylene Vinyl Acetate
Polymers 2017, 9(9), 397; https://doi.org/10.3390/polym9090397
Received: 11 August 2017 / Revised: 24 August 2017 / Accepted: 25 August 2017 / Published: 27 August 2017
Cited by 5 | PDF Full-text (2726 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, the dispersion of carbon nanotube (CNT) in ethylene vinyl acetate (EVA) is demonstrated to be significantly improved by the addition of octadecylamine (ODA)-grafted graphene oxide (GO) (GO–ODA). Compared to the CNT/EVA composite, the resultant GO–ODA/CNT/EVA (G–CNT/EVA) composite shows simultaneous increases [...] Read more.
In this paper, the dispersion of carbon nanotube (CNT) in ethylene vinyl acetate (EVA) is demonstrated to be significantly improved by the addition of octadecylamine (ODA)-grafted graphene oxide (GO) (GO–ODA). Compared to the CNT/EVA composite, the resultant GO–ODA/CNT/EVA (G–CNT/EVA) composite shows simultaneous increases in tensile strength, Young’s modulus and elongation at break. Notably, the elongation at break of the G–CNT/EVA composite still maintains a relatively high value of 1268% at 2.0 wt % CNT content, which is more than 1.6 times higher than that of CNT/EVA composite (783%). This should be attributed to the homogeneous dispersion of CNT as well as the strong interfacial interaction between CNT and EVA originating from the solubilization effect of GO–ODA. Additionally, the G–CNT/EVA composites exhibit superior electrical conductivity at low CNT contents but inferior value at high CNT contents, compared to that for the CNT/EVA composite, which depends on the balance of CNT dispersion and the preservation of insulating GO–ODA. Our strategy provides a new pathway to prepare high performance polymer composites with well-dispersed CNT. Full article
(This article belongs to the Special Issue Processing-Structure-Properties Relationships in Polymers)
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