Jian-Min Feng

Tensile properties of poly(ethylene terephthalate) and polyethylene in-situ microfiber reinforced composite formed via slit die extrusion and hot-stretching

This article dealt with the tensile properties of in-situ microfiber-reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The MRC was prepared through slit die extrusion and hot-stretching, followed by injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the formed microfibers. As expected, the tensile modulus and strength of PET/PE MRC can be significantly elevated at some composition. On the other hand, the reinforcement is heavily dominated by PET concentration; neither low nor high PET content was desirable for reinforcement. Results from elongation tests showed that the ultimate elongation between the samples with mincrofiers and spherical particles at some PET concentrations was extremely different, which was illustrated by the model proposed in which great slippage between the particles and the matrix occurred for the system with spherical particles, whereas there was no slippage between the microfibers and the matrix for MRC.

Morphology of in situ poly(ethylene terephthalate)/polyethylene microfiber reinforced composite formed via slit-die extrusion and hot-stretching

This article introduced the morphologies of in situ microfiber reinforced composite (MRC) based on poly(ethylene terephthalate) (PET) and polyethylene (PE). The PET/PE MRC was prepared through slit-die extrusion and hot-stretching, followed injection molding at the processing temperature of PE matrix, far below the melting temperature of PET in order to maintain the microfibers. Morphological observation indicated that the PET microfibers could be achieved by the way used in this study, and the microfiber characteristics, such as diameter, diameter distribution, were mainly dominated by PET content at a fixed hot-stretching ratio (HSR) of 19.17. Increasing the PET content the fiber diameter became bigger and the diameter distribution wider, but the minimum fiber diameter always remained constant.

Effect of Processing Method on Morphological and Rheological Properties of PC/CaCO3 Nanocomposites

The focus of this work is to investigate the effect of different manufacturing methods on nanoparticles dispersion and rheological properties of polycarbonate (PC) filled nano-calcium carbonate (CaCO3) nanocomposites. Two methods were used to prepare the PC/CaCO3 nanocomposites through twin-screw extruder: one was compounding PC with CaCO3 nano-powder, named PC-CP; another was compounding PC with CaCO3 aqueous suspension, named PC-CAS. The relationship between the processing method and the particle dispersion, matrix molecular weight and rheological properties of the nanocomposite was discussed. Morphological observation showed that nanoparticles were dispersed more homogeneously in PC-CAS. Gel permeation chromatography (GPC) test showed that molecular weight drop of PC-CAS was smaller than PC-CP when CaCO3 content under 2.2 wt%. Melt flow rate (MFR) and capillary rheological behavior indicated the change of rheological property of PC-CP was larger than PC-CAS while CaCO3 content under 2.6 wt%. In general, both the dispersion and rheological property of PC-CAS were better than PC-CP under a reasonable CaCO3 content.

Rheological Properties of PC/EVA Blend Compatibilized with the Transesterification

The rheological properties of PC/EVA blends had been investigated by a Haake torque rheometer. The effects of blending temperature, a polycarbonate and a catalyst on the rheological properties of PC/EVA blends were discussed. The transesterification between PC and EVA, catalyzed by dibutyl tin oxide (DBTO), were investigated by differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The results indicate that the chain break of PC or EVA can be accelerated by DBTO, which induces the equilibrium torque of PC or EVA to decrease as the DBTO content increases. But for the PC/EVA blend, as the blending temperature of increases, the increase of viscosity induced by the generation of the PC-EVA copolymer exceeds the decrease of viscosity induced by the chain break of PC and EVA. Therefore, the equilibrium torque of the PC/EVA blend with varying DBTO content is higher than that of uncatalyzed PC/EVA blend at the higher temperature, 250°C, compared with the lower temperature, 210°C. The content of PC in the blend influences the probability of transesterification and the generation of PC-EVA copolymer. The PC/EVA blend with 50 wt. %PC has the highest torque compared with the other blends.

Influences of Tensile Deformation Rate on Deformation and Morphology of Injection Molded 15/85 (by Weight) PC/PE and PET/PE Blends with High Interfacial Contact

Abstract Through the lower‐melting temperature component processing (LTCP) of the blends (where the processing temperature of the lower‐melting temperature component in a blend is used), high interfacial contact (pseudo‐adhesion) in poly(ethylene terephthalate) (PET)/polyethylene (PE) and polycarbonate (PC)/PE blends is obtained from the difference in the contraction of the dispersed particles and the matrix during cooling from the processing temperature to room temperature. As a result of the pseudo‐adhesion, the tensile strength and modulus of the PET/PE and PC/PE blends with high interfacial contact are superior to those of their corresponding classical blends and, additionally, the PC reinforcement on the matrix is more noticeable than the PET. Morphological observation indicates that during uniaxial deformation at a tensile rate of 50 mm/min, numerous PC microfibers are in situ formed in the PC/PE blend, whereas in the PET/PE blend, ellipsoidal particles appear, resulting from slippage taking place between the PET particles and the matrix. When the tensile rate is higher or less than 50 mm/min, the extent of plastic deformation for both PC and PET particles reduces. During elongation, for the PET/PE blend, necking first takes place at a point close to the non‐gate end of the specimens; subsequently the necking (cold drawing) spreads uniformly from this point at tensile rates of 10 and 50 mm/min. On the other hand, for the PC/PE blend at these two tensile rates, the position of the necking zone and the necking extension are irregular, and generally, the whole zone between the two grips is deformed gradually. As the tensile rate is increased to 300 mm/min, both blends fracture in a brittle manner.

Structure and Properties of Radiation Cross-Linked Polypropylene Foam

Polypropylene (PP) sheets obtained through a two-step process (masterbatch method) were crosslinked by electron beam irradiation. The crosslinked PP sheets were foamed in an oven under different processing conditions. The effects of foaming temperature and time on the mechanical properties and cell structure of PP foams were studied. With the foaming temperature increasing and foaming time lengthening, both the compression modulus and compression strength dropped. Scanning electron microscope (SEM) was employed to study the morphology and cell structure of different samples and the related morphology parameters were acquired. The results showed there was an optimum temperature and time that produced the maximum expansion ratio or the minimum foam density. As foaming temperature or time increased, the cell size increased and the cell density decreased regularly. Excessively high foaming temperature and overly long foaming time caused the coalescence and even the collapse of the cells.

The coupling relation between chain architectures and secondary flow field determined by an unusual dependence of shish-kebabs on molecular weight of high-density polyethylene

Selecting high molecular weight has become a quite popular approach for effective tuning of more shish-kebabs in semi-crystalline polymers. However, here, an unusual dependence of shish-kebabs on molecular weight of high-density polyethylene (HDPE) is found under the injection molding with a secondary flow. Characterization with electron microscope and X-ray scattering of the crystal structures reveals that the richest shish-kebabs develop in the HDPE with medium high molecular weight (HMW) chains rather than in the HDPE with more HMW chains. Both macroscopic scales (fluid behaviors related to the intensity of flow) and molecular scales (rheological properties related to orientation and relaxation) need to be overall considered and a physical model has been proposed to explain how the coupling between the chain architectures and the secondary flow field contributes to the unusual phenomenon. The factors, such as molecular parameters, interfaces between dispersed phase, and matrix as well as the properties of filler, profoundly influence both the two scales, which can be employed to tune the morphology related to physical properties. These significant results provide a simple but effective morphology control technique under a secondary flow field.

Effect of Ultrafine Full-Vulcanized Powdered Rubber on the Properties of the Intumescent Fire Retardant Polypropylene

Ultrafine full-vulcanized powdered rubber (UFPR) was added into intumescent fire retardant polypropylene (IFR-PP) composites, and fire retardance, morphology, and properties of the composite were analyzed. Ammonium polyphosphate and pentaerythritol were used as the intumescent fire retardants (IFR). The mechanical properties (elongation at break increased from 70% to 110%) and the melt flowability of IFR-PP improved by adding a small quantity of UFPR (less than 0.5 phr) but decreased when the UFPR was more than 0.5 phr. At the same time, the fire retardance, as measured by the limiting oxygen index and the UL94 vertical test rating, and other mechanical properties decreased appreciably with adding UFPR. The reasons were analyzed by using SEM micrographs, and a model was proposed to explain the reasons.

Mechanical Properties of Glass Bead-Filled Linear Low-Density Polyethylene:

The tensile and impact properties of glass bead (GB)-filled linear low-density polyethylene (LLDPE) were studied in this article. The tensile stress–strain behaviors of GB-filled LLDPE composites do not show any obvious difference from that of pure LLDPE, but the overall mechanical properties of GB-filled LLDPE composites are improved quite a lot, which demonstrates that in a relatively small bead size range, the inorganic spherical particle can effectively increase the mechanical properties of LLDPE. The elastic modulus and the elongation to break are almost constant for various filler contents, while the yield strength greatly increases when the filler content is very low, and then remains at about that level up to a 20% filler concentration. After a sharp increase when the filler concentration is 5% by weight, the impact strength gradually increases with increasing filler content, and obtains a 40% improvement above the resin, showing significant toughening effect. Combining the effects of bead size and filler concentration studied on the mechanical properties of GB-filled LLDPE composites, it is found that for glass beads with relatively small particle size, the bead size plays a significant role, which seems to be inconsistent with some results from the literature. From investigation of the morphology of the filled specimen, it is found that though the glass beads are not surface treated, the glass beads used present quite good interfacial adhesion with the matrix LLDPE, and the distribution of the bead in the matrix is the main influencing factor on the mechanical properties of the LLDPE composites.

Study of the morphology and temperature-resistivity effect of injection-molded iPP/HDPE/CB composites

The relationship between morphology and temperature-resistivity effect of injection-molded isotactic polypropylene/high density polyethylene/carbon black (iPP/HDPE/CB) composites with special orientation structure is investigated in detail. The morphological variation induced by melting, disorientation, crystallization and movement of CB particles is responsible for the change of electrical conductivity of the iPP/HDPE/CB composites during the heating and cooling. The room temperature volume resistivity of the composites reduces markedly after a round of heating and cooling because the network is improved through morphological changes and movement of particles during annealing. The continuity of HDPE/CB phase and the effective concentration of the CB particles in HDPE simultaneously determine the temperature-resistivity effects of the composites. Samples with iPP/HDPE mass ratio of 50/50 achieve a better balance of the two factors, which results in more stable conductive properties varying with temperature.