Ethylene-octene copolymer/graphite composites: Electrical and thermal conductivities and flame resistance

A series of ethylene-octene copolymer (EOC) composites have been prepared by melt-mixing with different weight ratios of expandable graphite filler (0-50% by weight). Electrical conductivity [both alternating current (AC) and direct current (DC)] and thermal conductivity studies were carried out. Effect of filler loading and frequency on electrical conductivity was studied. DC conductivity has increased from 1.51x10-13 Scm-1 to 1.17x10-1 Scm-1. Percolation threshold by DC and also AC methods was observed at about 16 vol. % of the filler. Real part of permittivity was found to be decreasing with increase in frequency while conductivity was increasing. Thermal conductivity was also found to be increasing gradually from 0.196 to 0.676 Wm-1K-1 which is about 245% increase. Graphite not only increases the electrical and thermal conductivities but at and above 40 wt. %, also acts as a halogen-free, environmental friendly flame retardant. Horizontal burn rate was studied in detail with interesting results. Initially the addition of graphite increases the horizontal burn rate but above 35 wt. % of graphite the burning speed decreases. Shore-A hardness of EOC/graphite composites shows that even with high graphite loading, the hardness is increased from about 50 to 68 only so that the rubbery nature of the composite is not affected very much.P(ED2.1.00/03.0111

High-temperature study of radiation cross-linked ethylene-octene copolymers

Three ethylene–octene copolymers (EOC) with a wide range of octene content (17, 30, and 38 wt%) and with the same melt flow index of 1 g/10 min were cross-linked by e-beam radiation (in range 30–120 kGy). The testing methods comprised of rheology, a high-temperature creep test, an analysis of the gel content, and a dynamic mechanical analysis (DMA) test. It was discovered that copolymers with a high octene content attain a higher level of cross-linking density. Cross-linking influenced properties below Tm only marginally as seen from the DMA results. However, the properties above Tm were highly influenced as detected by high-temperature creep and rheology. Above Tm, without the presence of crystals, only the chemical bonds holding the amorphous chains together manifested a gradually decreasing creep at 150 °C with an increasing irradiation level. The loss factor (tanδ at 0.1 Hz) at 150 °C revealed a decreasing trend (or higher cross-linking level) with an increasing octene content. High-temperature results were supported by an increasing gel content with increasing octene content. Samples irradiated to 30 kGy dissolved completely in xylene but showed significantly changed rheological characteristics indicating only an increase in the molecular weight and branching. Analysis according to the Charlesby–Pinner equation revealed increased cross-linking to the scission ratio G(X)/G(S) for EOCs with a higher octene content. While the q0 value which relates to cross-linking changed only slightly, a significant decrease in the p0 value which relates to chain scission was discovered. © 2016, Springer-Verlag Berlin Heidelberg.Internal Grant Agency of the Tomas Bata University in Zlin [IGA/FT/2016/009

Polypropylene/Organoclay Nanocomposites Prepared by Supercritical CO2 Assisted Extrusion Process

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing co-rotating twin-screw extruder with the assistance of supercritical CO2 injection. The effect of molecular weight of PP-MA (maleic anhydride modified polypropylene) on clay dispersion and mechanical properties of nanocomposites were investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP-MA with the highest molecular weight. The basal spacing of clay inthe composites was measured by X-ray diffraction(XRD). Nano-scale morphology of samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and by optical microscopy at a fixed crystallization temperature. For well dispersed two-component system, PP- MA330k/clay, the crystallization kinetics and the spherulite size remained almost unchanged and the impact strength decreased with increasing the clay content. On the other hand, the intercalated three component system, PP/PP-MA330k/clay, containing some dispersed clay as well as the clay tactoids, showed much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. The influence of supercritical CO2 on mixing was evaluated together with the effect of initial melting temperature. Increasing initial melting temperature causes gradual decrease in bulk cristallization kinetics with exception of the 240-260°C temperature range for system without CO2. Optical microscopy revealed large number of small spherulites for system without CO2 after initial melting at 250°C. After 28 min of initial induction period of crystallization many small spherulites appeared in the vicinity of large spherulite for the system with CO2 indicating beginning of homogenous nucleation.P(ED2.1.00/03.0111),

Polypropylene/Organoclay Nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing co-rotating twin-screw extruder. The effect of molecular weight of PP-MA (maleic anhydride modified polypropylene) on clay dispersion and mechanical properties of nanocomposites were investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP-MA with the highest molecular weight.P(ED2.1.00/03.0111),

Influence of branching density in ethylene-octene copolymers on electron beam crosslinkability

Two ethylene-octene copolymers (EOC) with the same melt flow index (MFI = 3 g/10 min) but different octene contents, being 20 and 35 wt % (EOC-20 and EOC-35), were compared with regard to sensitivity to electron beam crosslinking. Dynamic mechanical analysis (DMA) revealed a large influence of the octene content on the storage modulus and the glass transition temperature (Tg) but a smaller influence of irradiation on the properties below melting point (Tm). Rheology at 150 °C pointed out large differences in samples crosslinked in the 0-60 kGy range and at lower frequencies (0.1-1 Hz). The loss factor tanδ confirmed that before irradiation the two copolymers were very similar, while after irradiation to 120 kGy, the EOC-35 had considerably lower tanδ than EOC-20, which corresponds to a better elasticity (or a higher level of crosslinking). A high-temperature creep test showed a considerably lower creep for EOC with a higher octene content. An analysis of the insoluble gel content exhibited higher values for EOC-35 confirming a higher level of crosslinking. Analysis according to the Charlesby-Pinner equation revealed increased crosslinking-to-scission ratio, G(X)/G(S), for EOC-35. While the G(X) value changed only slightly, a significant decrease in the G(S) value was discovered. © 2015 by the authors.Internal Grant Agency of the Tomas Bata University in Zlin [IGA/FT/2015/007

The development of powder injection moulding binders: A quantification of individual components' interactions

The study of interactions between binder system components is critical for improving the processing properties of powder injection moulding (PIM) feedstocks. In this paper the interactions between acrawax (AW) and polyethylene glycol (PEG) were analysed and compared with those obtained for carnauba wax (CW). Due to the complexity of interaction mechanisms, the polymers were substituted with their basic low molecular weight analogues and analysed by FTIR and calorimetry. Self-interaction energies and association energies were determined using calorimetric analysis. Shifts of FTIR absorption peaks (C-O stretch and N-H stretch) served as evidence of the presence of interactions between the components. The calorimetric study of AW/PEG analogues showed a temperature increase during mixing, indicating the presence of strong interactions. The combined data from FTIR and calorimetry allowed a quantitative evaluation, which indicated about two times stronger interactions between AW (with C. O and N-H groups) and PEG (with C-O and -OH groups), as compared to CW (with C. O and C-O groups) and PEG analogues. © 2015 Elsevier B.V.TBU in Zlin [IGA/FT/2015/001]; Operational Program Research and Development for Innovations; ERDF; National Budget of Czech Republic [CZ.1.05/2.1.00/03.0111

Influence of biodegradation on crystallization of poly (butylene adipate-co-terephthalate)

The biodegradation of aromatic-aliphatic biodegradable polyester poly (butylene adipate-co-terephthalate) (PBAT) was studied under mesophilic (37°C) and thermophilic (55°C) anaerobic conditions. Anaerobic sludge from municipal wastewater treatment plant was utilized as an inoculum. Non-isothermal crystallization kinetics of PBAT before and after biodegradation was explored by differential scanning calorimetry. Under mesophilic anaerobic conditions (37°C), the biodegradation after 126 days was only 2.2%, molecular weight changed from 93 000 to 25 500 g/mol, and the crystallization behavior was changed only slightly. However, biodegradation under thermophilic anaerobic conditions (55°C) caused much bigger changes: biodegradation according to biogas production reached after 126 days 8.3%, molecular weight changed from 93 000 to 9430 g/mol, and the crystallization behavior was changed significantly. While T m increased only slightly, T c on the other hand increased significantly for the sample after biodegradation at 55°C. Also, the crystallization rate was slower (particularly at lower cooling rates), but crystallinity was slightly higher. The diffraction pattern was observed by X-ray diffraction. © 2018 John Wiley & Sons, Ltd

Influence of electron beam irradiation on high-temperature mechanical properties of ethylene vinyl acetate/carbon fibers composites

The purpose of this study was to investigate the effect of carbon fiber (CF) and electron-beam (EB) radiation on high-temperature mechanical properties of ethylene-vinyl acetate (EVA). Polymer composites were prepared by mixing on a two-roll mill. After compression molding, the samples were irradiated between 60 and 180 kGy, and dynamic mechanical analysis (DMA) was used to characterize physical properties. The effects of filler content and radiation level on the mechanical properties of EVA/CF were evaluated. The shear stress and modulus were observed to increase with increasing of the filler level. However, there was a dramatic decrease in creep compliance. It was also shown that introduction of irradiation on EVA composite increases the shear stress and the real part of the dynamic shear modulus G' due to the increase in molecular weight and cross-linking of the polymer after irradiation. J. VINYL ADDIT. TECHNOL., 2019. © 2019 Society of Plastics Engineers. © 2019 Society of Plastics EngineersInternal Grant Agency [IGA/FT/2017/007]; Tomas Bata University in Zli

Ethylene-Octene Copolymers/Organoclay Nanocomposites: Preparation and Properties

Two ethylene-octene copolymers with 17 and 45 wt.% of octene (EOC-17 and EOC-45) were compared in nanocomposites with Cloisite 93A. EOC-45 nanocomposites have a higher elongation at break. Dynamical mechanical analysis (DMA) showed a decrease of tan δ with frequency for EOC-17 nanocomposites, but decrease is followed by an increase for EOC-45 nanocomposites; DMA showed also increased modulus for all nanocomposites compared to pure copolymers over a wide temperature range. Barrier properties were improved about 100% by addition of organoclay; they were better for EOC-17 nanocomposites due to higher crystallinity. X-ray diffraction (XRD) together with transmission electron microscopy (TEM) showed some intercalation for EOC-17 but much better dispersion for EOC-45 nanocomposites. Differential scanning calorimetry (DSC) showed increased crystallization temperature Tc for EOC-17 nanocomposite (aggregates acted as nucleation agents) but decrease Tc for EOC-45 nanocomposite together with greatly influenced melting peak. Accelerated UV aging showed smaller C=O peak for EOC-45 nanocomposites. © 2016 Alice Tesarikova et al.TBU in Zlin [TA03010799, IGA/FT/2015/007