Effect of thermotropic copolyesteramide on the properties of polyamide‐66/liquid crystalline copolyester composites

Liquid crystalline copolyester‐polyamide 66 (LCPES/PA66) composites compatibilized by liquid crystalline copolyesteramide (LCPEA) were prepared by injection molding. The LCPES employed was a commercial copolyester, Vectra A950, and the LCPES was a semiflexible thermotropic copolyesteramides based on 30 mol% of p‐amino benzoic acid (ABA) and 70 mol% of poly(ethylene terephthalate) (PET). Thermal analysis, mechanical characterization, and morphological investigations were conducted on the blends. The dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) tests showed that LCPEA is an effective compatibilizer for the LCPES/PA66 composites. The mechanical measurements showed that the stiffness, tensile strength and Izod impact strength of the in‐situ composites are improved by adding LCPEA because of the compatibilization and reinforcement to LCPES/PA66 composites. However, the properties improvement vanished when LCP content reached 10 wt%. The drop weight dart impact test was also applied to analyze the impact fracture characteristics of these composites. The results showed that the maximum impact force (F_max), crack initiation and propagation energy all improved with the addition of a small percent of LCPEA. From these results, it appeared that LCPEA prolongs the time for crack initiation and propagation. It also increases the energies for crack initiation and propagation, thereby leading to toughening of the LCPES/PA66 in‐situ composites. Finally, the correlation between the mechanical properties and morphology of the composites is discussed.     

微珠填充LDPE复合物的拉伸弹性模量

研究了填充低密度聚乙烯中玻璃微珠含量及其大小对复合体系拉伸弹性模量Ｅ的影响。结果表明，Ｅ随着微珠含量ω的增加呈非线性函数形式增大，而微珠直径对Ｅ的影响较为复杂。基于实验结果提出了一套描述Ｅ与ω关系的数学模型。     

Synthesis and characterization of alternating copolymer from carbon dioxide and propylene oxide

High yield and pure zinc glutarate catalysts used for copolymerization of carbon dioxide and propylene oxide have been synthesized in different solvents by ultrasonic methodology. For the purposes of comparison, low‐yield zinc glutarates were also synthesized via mechanical stirring method with other synthetic conditions remaining unchanged. Fourier Transform Infrared Spectroscopy and wide‐angle X‐ray diffraction techniques confirmed the presence of high‐quality zinc glutarate catalysts. Accordingly, poly(propylene carbonate) (PPC) can be synthesized from carbon dioxide and propylene oxide using the zinc glutarate catalysts. It was confirmed that the as‐prepared PPC had an alternating copolymer structure together with high molecular weight. The thermal and mechanical properties of the obtained PPC copolymer were determined by means of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and tensile test. DSC and TGA results showed that the PPC copolymer exhibited high glass transition temperature (39.39°C) and decomposition temperature (278°C) when compared to their corresponding values reported in the literature. Tensile test showed that the PPC film exhibited superior mechanical strength. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2327–2334, 2002     

Melt processable and biodegradable aliphatic polycarbonate derived from carbon dioxide and propylene oxide

Alternating poly(propylene carbonate)s (PPC)s were successfully synthesized from carbon dioxide and propylene oxide in higher yield than previously reported. Such thermally stable and high molecular weight copolymers were achieved by optimizing the reaction conditions. The molecular structural change and mechanical properties of the alternating copolymer subjected to melt extrusion were examined by means of modulated differential scanning calorimetry (MDSC), thermogravimetric analysis (TGA), NMR, and tensile tests. The MDSC and TGA results showed that the alternating copolymer generally exhibits a high glass‐transition temperature of above 40°C and a decomposition temperature of above 250°C. These PPCs can be readily melt processed under conditions similar to those for commercial polyolefins. For instance, they can be melt extruded in a temperature range from 150 to 170°C under varying extrusion pressures. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3301–3308, 2003     

Effect of Natural Fiber Network on Permeability and Tensile Strength of Composites through Vacuum Infusion Process

This investigation is primarily focused to study the effect of fiber network on the permeability in vacuum infusion molding process. The unsaturated permeability of several natural fiber mats with different networks is measured. The experimental permeabilities are fitted by the Kozeny model and contact angle model. The outcome highlighted that the contact angle model shows more precise results as compared to kozeny model. The obtained permeability for the random fiber mats shows higher values than directional fiber mat. Furthermore, the maximum increase in tensile strength is observed in the unidirectional composites and the flow along the fiber direction.     

Tensile properties and morphology of PP/EPDM/glass bead ternary composites

The tensile properties of three types of injection molded glass bead (GB) filled polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) ternary composites have been determined at room temperature by using an Instron materials testing machine. The effects of the filler surface treatment, the glass bead (GBI) pretreated with a silane coupling agent and the EPDM (EPDM-MA) modified with a maleic anhydride, and the filler content on the tensile mechanical properties of the ternary PP composites have been investigated. The Young's modulus (E_c) increases while the yield stress (σ_yc) and tensile fracture strength (σ_bc) of the composites decrease with increasing the volume fraction of glass beads (ϕ_g) when the volume fraction of EPDM is constant (ϕ_e = 10%). The (E_c) values of PP/EPDM/GBI and ϵ_bc for PP/EPDM-MA/GB2 (no surface pretreated) systems are the highest at the same ϕ_g. The tensile fracture energy (E_bc) and tensile fracture strain (ϵ_bc) of PP/EPDM/GBI and PP/EPDM/GB2 systems appear to peak at ϕ_g = 25%. However, the E_bc and ϵ_bc of PP/EPDM-MA/GB2 system show little changes with increasing ϕ_g. The fracture surfaces of ternary composites have been examined in a scanning electron microscope. The correlation between the tensile properties and morphologies of these materials have been discussed.     

Rheology and impact characteristics of compatibilized polypropylene-liquid crystalline polymer composites

Polypropylene-liquid crystalline polymer (PP/LCP) and maleic anhydride compatibilized PP/LCP blends were prepared using the extrusion technique followed by injection molding. The LCP employed was Vectra A950 which consists of 25 mol % of 2,6-hydroxynaphthoic acid and 75 mol % of p-hydroxybenzoic acid. The rheology, morphology, and impact behavior of compatibilized PP/LCP blends were investigated. The rheological measurements showed that the viscosity of LCP is significantly higher than that of the PP at 280°C. This implied that the viscosity ratio of the LCP to the polymer matrix is much larger than unity. Scanning electron microscopy (SEM) observations revealed that the LCP domains are dispersed mainly into elongated ellipsoids in the PP/LCP blends. However, fine fibrils with large aspect ratios were formed in the compatibilized PP/LCP blends containing LCP content ≥ 10 wt %. The development of fine fibrillar morphology in the compatibilized PP/LCP blends had a large influence on the mechanical properties. The Izod impact strength of the PP/LCP blends showed little dependence on the LCP concentrations. On the other hand, the impact strength of the compatibilized PP/LCP blends was dependent on the LCP concentrations. The correlation between the LCP fibrillar morphology and spherulitic structure with the impact properties of the compatibilized PP/LCP blends is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 521–530, 1998     

Crystallization behavior of glass bead‐filled low‐density polyethylene composites

The effects of the filler content and the filler size on the crystallization and melting behavior of glass bead‐filled low‐density polyethylene (LDPE) composites have been studied by means of a differential scanning calorimeter (DSC). It is found that the values of melting enthalpy (ΔH_c) and degree of crystallinity (x_c) of the composites increase nonlinearly with increasing the volume fraction of glass beads, ϕ_f, when ϕ_f is greater than 5%; the crystallization temperatures (T_c) and the melting temperatures (T_m) of the composites are slightly higher than those of the pure LDPE; the effects of glass bead size on x_c, T_c, and T_m are insignificant at lower filler content; but the x_c for the LDPE filled with smaller glass beads is obviously greater than that of the filled system with bigger ones at higher ϕ_f. It suggests that small particles are more beneficial to increase in crystallinity of the composites than big ones, especially at higher filler content. In addition, the influence of the filler surface pretreated with a silane coupling agent on the crystallization behavior are not too outstanding at lower inclusion concentration. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 687–692, 1999     

Crystallization kinetics of compatibilized blends of a liquid crystalline polymer with polypropylene

Blends of a maleic anhydride-grafted polypropylene (m-PP) and a liquid crystalline polymer (LCP) based on a copolyester of hydroxynapthoic acid and hydroxybenzoic acid were fabricated. The morphology and isothermal and nonisothermal crystallization kinetics behavior of the m-PP copolymer and m-PP/LCP blends were investigated using polarizing optical microscopy, depolarized light intensity, and differential scanning calorimetry. A polarizing optical micrograph revealed that the m-PP is very effective to promote a finer dispersion of the LCP phase in the PP matrix. Consequently, the LCP domains or fibrils acted as potential sites for the spherulite nucleation. The isothermal kinetics measurements also indicated that the rate of crystallization is enhanced in the maleated PP/LCP blends which exhibit transcrystallinity. In general, the nonisothermal kinetics results were in good agreement with those obtained from the isothermal kinetics measurements. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 707–715, 1997