Band 32, Heft 3

Compatible blends of isotactic polypropylene (iPP)/low-density polyethylene (LDPE)/ethylene-propylene-diene monomer (EPDM) were prepared by reactive blending in the presence of dicumyl peroxide (DCP). The blends were characterized using different techniques: dynamical rheological analysis (DRA), differential scanning calorimetry (DSC), optical microscopy (OM) and scanning electron microscopy (SEM), dynamical mechanical thermal analysis (DMTA), viscosity and impact strength, to evaluate their properties. Results revealed that the presence of the peroxide in LDPE/EPDM blends gives rise to crosslinking reactions, as is the case in iPP/LDPE/EPDM blends. However, in the latter case, scission reactions of the iPP component also take place. As a consequence of the whole process, morphological changes arise mainly in the amorphous regions, without affecting the degree of crystallinity of the components. The mechanical properties of the blends are consequently improved, due to the crosslinked network thus formed in the blends.

Crystallization processes of polylactide (PLA)/acid oxidized multiwalled carbon nanotube (A-MWCNT) composites were detected by dynamic rheological measurements. The influences of pre-shear, crystallization temperature, concentration and aspect ratio of A-MWCNT, on the crystallization kinetics of PLA, were investigated. The addition of small amounts of A-MWCNT, can more or less accelerate the crystallization of the PLA matrix. Composites with smaller aspect ratio A-MWCNT (A-MWCNT–S) show faster crystallization rates than those with larger aspect ratio A-MWCNT (A-MWCNT–L), due to the more heterogeneous nucleation sites of the former. Pre-shear can significantly promote the crystallization process of PLA composites, and with the increase in shear rate, the crystallization rate becomes faster. Pre-shear results in an accelerated crystallization compared to PLA/A-MWCNT–S composites at the same concentration, without pre-shear, due to a more serious deformation from entanglement to orientation of A-MWCNT–L.

A continuous open structured network, with a high surface area, low solids fraction, and nano-scale domain morphology, was observed to grow from dissolved blend components on cold fractured surfaces of immiscible polymer blends, when reacted with dimethylformamide (DMF). In this work, we showed that the network is comprised of polymethyl methacrylate (PMMA), with a strong glassy character similar to or even in excess of conventional PMMA pellets used in the preparation process, in contrast to the amorphous but not glassy PMMA produced when similar materials were synthesized away from the PMMA host. Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC) analyses confirmed the chemical and physical character of the network. This general network formation phenomenon, which was initially observed in PMMA/high density poly ethylene (HDPE) blends produced by conventional extrusion, PMMA/HDPE blends compression molded from powder precursors, and subsequently on bulk PMMA, produces a unique structure that has potential applications as an interfacial modification substance or as a functional material in biomaterials and catalysis.

Abundantly available rice husk can be used with polypropylene for the development of thermoplastic composites. The present study deals with mechanical properties such as hardness and impact strength of rice husk polypropylene composites with the addition of talc, mica, CaCO 3 , wollastonite, and zirconium oxide. Maleic anhydride polypropylene was used as compatibilizer. Improvement in the hardness and impact strength of the composites was observed by the use of these additives. Possible applications of rice husk polypropylene composite are in building and automobile sectors.

This paper focuses on experimental investigation and modelling of the unusual creep and relaxation behaviour of polypropylene. A polypropylene specimen was loaded up to three different levels of maximum strain ( ɛ max ), unloaded to various minimum stresses ( σ min ), creep and relaxation tests were performed at seven different strain levels. In addition to investigate the effect of loading history on unloading paths, multiple creep experiments were conducted at various stress levels. It was observed that unusual creep and relaxation behaviour of polypropylene depended on a strain increment (Δ ɛ ) which is the difference between the minimum ( ɛ min ) and maximum strain level ( ɛ max ). Increasing the strain increment affects the creep and relaxation behaviour on loading path. As a result, the creep and relaxation behaviours of polypropylene show non-monotonic characteristics. The viscoplasticity theory based on overstress for polymer (VBOP) model was used to model the unusual creep and relaxation behaviour of polypropylene. From the comparison between the VBOP model predictions and the experimental results, it can be seen that the VBOP model can model both the unusual creep and relaxation behaviours of a semicrystalline polymer.

The objective of this research was to investigate the effect of incorporating nanofiller, montmorillonite (MMT) on mechanical, morphological and rheological properties of acrylonitrile-butadiene-styrene (ABS) and recycled poly(ethylene terephthalate) (rPET) nanocomposites. The MMT contents in 70:30 ABS/rPET and 30:70 ABS/rPET ranged from 1 to 5 wt%. The ABS/rPET nanocomposites were extruded and injection-molded into tensile, flexural and impact test samples. Samples underwent rheological testing by using melt flow index (MFI) and capillary rheometer and the morphology of the nanocomposites was investigated by using field emission scanning electron microscopy (FESEM). The maximum tensile strength and flexural strength were at 1 wt.% of MMT for both blends. However, tensile modulus and flexural modulus reached maximum point at 3 wt.% and started to decrease beyond 3 wt.%% of MMT. Impact strength for both blending decreased significantly with the incorporation of MMT. MFI values decreased with the increment of MMT for 30:70 ABS/rPET, but increased for 70:30 ABS/rPET. The incorporation of MMT increased the melt strength of 30:70 ABS/rPET nanocomposites. Shear viscosity showed increment with the increasing MMT concentration for 30:70 ABS/rPET nanocomposites. However, shear viscosity decreased with the increment of MMT for 70:30 ABS/rPET. FESEM micrographs show good distribution and dispersion of MMT in 30:70 ABS/rPET, but poor dispersion and agglomeration of MMT in 70:30 ABS/rPET.

Metallocene polyethylene (mPE)/silica ternary nanocomposites were prepared via a melt mixing approach using two types of modifiers, mPE-g-MA (maleic anhydride) or linear low density polyethylene (LLDPE)-g-MA. Transmission electron microscopy revealed a similar degree of silica dispersion status for mPE/silica with or without modifiers to suggest the similar compatibility for mPE with modified silica, as evidenced by a similar change on the master curves over the corresponding frequency range and silica content in Cole-Cole plots. Silica and the modifiers served as nucleating agents to increase the crystallization temperature of mPE. Two visible crystallization temperatures or melting temperatures corresponding to mPE and LLDPE-g-MA, respectively, were still observable for LLDPE-g-MA modified cases, but not for mPE-g-MA modified cases. LLDPE-g-MA modified cases rendered the highest Young’s modulus and cutting strength due to the induced yielding from the high crystalline LLDPE-g-MA. Cutting strength of the LLDPE-g-MA modified case was approximately 34% larger than that of the mPE-g-MA modified case at 10 phr silica. By contrast, mPE-g-MA modified cases rendered the highest tear strength due to its high flexibility to provide more physical entanglements. Strength of investigated nanocomposites varied under different deformation behaviors to signify the importance of interphase and matrix variation at similar silica dispersion status.

Polyamide-imide (PAI) polymer is a high-temperature resistant polymer, which is used as contact breaker material because of its high electrical insulation property. The working conditions of contact breakers arise from the wear and friction problem conditions of these materials. Therefore, the tribological behavior of PAI polymer is important. In this study, the friction and wear performance of pure PAI polymer and PAI composite [PAI+12% graphite+3% polytetrafluoroethylene (PTFE)] were studied in two different cooling environmental conditions (with and without air cooling). Wear tests were carried out with the configuration of a polymer pin, on a rotating AISI 316 L stainless steel disc. Test conditions were atmospheric conditions, 50 N, 100 N, and 150 N loads and 0.5, 1.0, 2.0 and 3.0 m/s sliding speeds. For sliding without air cooling and sliding with air cooling, the results show that the coefficient of friction and wear rates for pure PAI and PAI+12% graphite+3% PTFE composite, slightly decrease and increase with the increase in applied load and sliding speed values, respectively. In addition, for the range of loads and sliding speeds of this study, low coefficients of friction and high specific wear rates are registered at sliding under air cooling conditions. Finally, the wear mechanism includes adhesive and abrasive processes.

A branched copolyester was synthesized using dimethyl terephthalate (DMT), 2,2-bis[4-(2-hydroxypropoxy)phenyl]propane, ethylene glycol (EG) and 2-(hydroxymethyl)-2- ethylpropane-1,3-diol (trimethylol propane, TMP). The branched copolyester and p -phenylene diisocyanate (PPDI) were melt extruded to enhance the melt viscosity and elasticity for use as a toner binder in the laser printing process. The effects of PPDI content on melt, thermal and rheological properties of the chain-extended copolyester were investigated. The melt flow index (MI) decreased with increasing amount of PPDI, due to a reaction between the hydroxyl chain end and isocyanate group. The storage modulus, loss modulus and complex viscosity of the chain extended copolyester were higher and the modified Cole-Cole plots revealed the chain extended copolyester to have higher elasticity than that of the branched copolyester. The chain extended copolyester exhibited suitable melt and rheological properties for applications as a toner binder in the laser printing processes.

No abstract available.