The thermal mechanical properties and morphological changes of modified poly(lactic acid) (PLA) and polycarbonate (PC) polymer blends based on the equal weight fraction of each component were investigated. Several blend samples were prepared by melt processing with a twin screw extruder using both poly(butylene succinate-co-lactate) (PBSL) and epoxy (EP) as compatibilizers for the PLA/PC binary system. Differential scanning calorimetry (DSC) of PLA/PBSL and PC/PBSL binary blends showed that individual components were immiscible. Scanning electron microscopy (SEM) analysis of these blends revealed the domain size of PBSL was $ 0.5-1 lm in PLA/PBSL blend, and reduced to around 0.1 lm in PC/PBSL blend. The notched Izod impact strength (IS) of PLA/PC/PBSL ternary blends increased with PBSL content up to 10 phr PBSL due to enhanced interfacial interaction and proper domain size of the dispersed phase on the basis of DMA, DSC, and SEM analysis. The heat deflection temperature (HDT) showed a maximum at 5 phr PBSL, and it dropped with increasing PBSL content which is a ductile polymer. However, the HDT of PLA/PC/EP ternary blends increased considerably with 10 phr EP due to rigid interphase formation, and it increased further with 1 phr quaternary amine catalyst, however, the IS dropped nearly the same as that of unmodified PLA/PC blend. To take advantage of the two compatibilizers, PBSL and EP were added to the PLA/PC blend at 10 phr each plus 1 phr catalyst and both IS and HDT were improved significantly over unmodified PLA/PC pair.
Poly(butylene succinate‐co‐L‐lactate) (PBSL)–compatibilized poly(L‐lactide) (PLLA) polymer blends with two commercial grades of polycarbonate (PC) were investigated. The capillary tests showed that the steady shear viscosity of high molecular weight PC (PC‐L) was 10 times higher than that of low molecular weight PC (PC‐AD) throughout the shear rate range under investigation. Morphologic examination revealed that the shape of the dispersed PC‐L phase in the as‐extruded blends was largely spherical, but the PC‐AD phase was more like a rod and elongated further during injection molding. Notched Izod impact strength (IS) of the unmodified PLLA/PC‐L blend was higher than that of PC‐AD blend. The IS of modified ternary blends increased with PBSL content because of enhanced phase interaction indicated from thermal and morphologic analysis. The PBSL modification also enhanced IS more significantly in PLLA/PC‐L than in PLLA/PC‐AD blends. On the contrary, the heat deflection temperature (HDT) of PLLA/PC‐L binary system was much lower than that of PLLA/PC‐AD. HDT of PBSL‐modified PLLA/PC‐AD blends dropped with increasing PBSL content, which is a ductile polymer. Thermal and dynamic mechanical analysis of the ternary blends showed that individual components were immiscible with distinct Tgs for PC and PLLA and distinct Tms for PBSL and PLLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers
The compounding of wood flour filled polyethylene is discussed with reference to co-rotating twin-screw extruders from two manufacturers. An acrylic acid-grafted polyethylene (PE-HD-AA) copolymer was used as the compatibilizer in high density polyethylene wood flour (PE-HD/WF) composite system. Special consideration was given to the compounding of the heat- and shear-sensitive wood flour. The relevant screw configuration was found to consist of short mixing length with low intensity of shearing. A suitable combination of processing variables was necessary for limiting the thermal degradation of the wood filler, however, tensile properties of the composites were not affected much. Furthermore, the allowable range of processing temperature was limited, and there was an upper bound of rotating speed and a lower bound of throughput rate within which the darkening of wood filler in the composites was acceptable. The processing window was also experimentally constructed in terms of the degree of darkening of wood composites.
Conductive polymer composites have aroused wide interests from both academia and industry in the field of functional materials. Addition of diverse conducting fillers such as carbon black [1,2], graphite [3], and metal fiber or powder [4] into thermoplastic polymers through melt mixing is an effective approach to fabricate conductive composites. Because a great amount of the fillers, generally greater than 15 wt% [5], were required for the host polymer to become conductive, resulting in both poor processability and inferior mechanical properties, the practical applications of these conventional composites were largely restricted. On the other hand, commercial exploitation of isotactic polypropylene has been expanded rapidly due to its attractive characters of low cost, low weight, heat distortion above 100°C, and extraordinary versatility in terms of properties, applications and recycling. The introduction of nanoscopic fillers of high anisotropy enhances a wide range of performance of the polypropylene nanocomposites, such as mechanical, thermal and conductive properties, at a relatively small loading [6]. Graphite is a layered mineral composed of weakly bonded graphene sheets with a large aspect ratio. Abstract. Various surfactants of different molecular weights, including alkylamine, poly(oxypropylene) diamine (POP), and maleic anhydride grafted polypropylene (PPgMA) oligomers, were used for simultaneous funtionalization and reduction of graphite oxide (fGO). In this study, the effect of molecular weight and compatibility of the surfactants on the morphology and properties of the nanocomposites are reported. Wide-angle X-ray diffraction (WAXD) exhibited a definite interlayer thickness for GOA (alkylamine intercalated GO), however, the diffraction peaks were nearly suppressed for fGOs combining ODA with either POP (GOAP) or PPgMA (GOAE). The uniform dispersion of the fGO flakes in the polypropylene matrix resulted in the significant increase in both the degradation temperature and the crystallization temperature. A single characteristic melting peak of monoclinic (!) crystalline phase was observed from DSC traces, which was consistent with WAXD results. Dynamic mechanical analysis clearly indicated increase in both the storage modulus and the glass transition temperature of the nanocomposites due to the enhanced affinity between fGO and the polypropylene matrix. However, GOAP composite showed lower E" and T g than GOAE because POP is less compatible with the matrix than PPgMA oligomer. Dielectric analysis also showed significant increase in both dielectric permittivity and dielectric loss at low frequency regimes with GOAE showing maximum dielectric properties. The finely dispersed GOAE and its compatibility with polymer matrix manifested the interfacial polarization, which gave rise to much greater #" and #$ than other nanocomposites.
The isothermal flow of plastic fluids in coathanger dies is studied. A general three-dimensional finite element code is developed for the flow analysis purpose. The pressure distribution, the velocity distribution and the transverse flow rate distribution are calculated. The yield value of filled compounds gives rise to a mobile plug in the flow channel. The development of plug zone along the flow direction is also shown by the finite element analysis. The effect of the die geometry on the transverse flow rate distribution is critically discussed. It is found that the cross sections of the flow channel in a coathanger die has the shape of a dog bone or a dumbell which make a nearly even transverse flow rate distribution possible.
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