Injection Molding Shrinkage and Mechanical Properties of Polypropylene Blends

Polypropylene (PP) blends based on isotactic polypropylene (iPP), propylene-ethylene block copolymer (bPP), and propylene–ethylene random copolymer (rPP) were prepared by melt blending and the effects of content of bPP and rPP on the shrinkage during solidification and storage and mechanical properties of the blends were studied. It was found that the addition of polypropylene copolymer could effectively reduce the processing shrinkage of iPP and the lowest shrinkage of the blends was achieved at a loading of 2 wt% bPP or rPP. The flexural modulus and tensile strength of the blends decreased a little while the impact strength and elongation at break were improved greatly compared with those of iPP.     

Polymer-filler interaction and control of structure in barium sulphate-filled blends of polypropylene

The structure of barium sulphate-filled immiscible blends with a polypropylene (PP) matrix can be controlled with respect to the occlusion of the filler with the aid of maleic anhydride-grafted polypropylene (PP-g-MAH) through the formation of an interlayer around the filler particles. Here we analyze the interlayer and the mechanism of interlayer formation in a blend with a poly(methylmethacrylate) (PMMA) dispersed phase and compare the results with previous studies, which concerned PP blends with polystyrene (PS) and poly(styrene-co-acrylonitrile) (SAN) minority phases. The main analytical tools were scanning electron microscopy (SEM), dynamic mechanical analysis (DMA) and Fourier Transform Infrared Spectroscopy (FTIR). The filler is occluded in the PMMA polymer in the PP/PMMA/BaSO₄ (60/20/20 vol.%) blend, but is occluded in the PP phase at the addition of a sufficient amount of PPg-MAH. The reason for the formation of the latter structure is a PP-g-MAH layer surrounding the filler particles, and the most likely mechanism behind this phenomenon is judged to be specific weak interactions between carbonyl groups in the graft copolymer and Ba²⁺ ions at the filler surface.     

Antibacterial and Miscibility Properties of Chitosan/Collagen Blends

The miscibility, bioactivity, and antibacterial properties of chitosan/collagen specimens were systematically studied. The specimens were prepared by blending collagen and chitosan with varying deacetylation degrees in solutions; the collagen molecules had been extracted from pigskins using the acid swelling-pepsin digestion method. To understand the miscibility properties of collagen and chitosan molecules, the intrinsic viscosity and differential scanning calorimetry analysis of collagen, chitosan, and collagen/chitosan specimens were performed. The instrinsic viscosity measurements suggested that chitosan and collagen molecules with varying deacetylation degrees were miscible at molecular level for all compositions and degrees of deacetylation of chitosan/collagen mixture solutions prepared in this study. Fourier transform infrared analyses suggested that the percentage of preserved triple helix structures present in collagen molecules in collagen/chitosan specimens decreased with increasing chitosan contents, since the ratios of peak absorbance at 1239 cm^?1 of amide III and 1455 cm^?1 of C?H bending of collagen/chitosan specimens decreased significantly with increase in their chitosan contents. Abnormally high denaturation temperatures (T_d) were observed as the chitosan contents of collagen/chitosan specimens reached 40 wt%, at which T_d of collagen molecules was even higher than that of the corresponding pure chitosan molecules with varying deacetylation degrees. The antibacterial activity of collagen/chitosan blends increased consistently with increasing deacetylation degrees and concentrations of chitosan molecules in collagen/chitosan solutions. Possible explanations for these interesting thermal denaturation, antibacterial, and miscibility properties of chitosan/collagen specimens are reported.     

Percolation Thresholds in Ternary Polymer Melt Blends with Separate Dispersions of the Inner Phases: Mathematical Model

A mathematical model based on a straightforward geometrical background is developed which enables predictions of a transition of one dispersed phase to a cocontinuous one (i.e., the percolation threshold) on addition of another dispersed phase during melt mixing in ternary polymer blends. The present work concerns only ternary blends with two separate dispersions of the inner phases in which no encapsulation takes place. In addition, in order to simplify the model, one of the inner phases was represented by hard, nondeformable microspheres The expression developed describes well an experimental relationship between the percolation threshold, the concentration above which the former dispersed phase transforms to a continuous one, and concentrations of both inner phases. The results agree well with the experimental data obtained in a previous work.     

极低密度聚乙烯与其它聚乙烯的共混

从结构角度，用ＤＳＣ，ＷＡＸＤ，ＳＡＸＳ研究了聚乙烯（ＰＥ）家族中极低密度聚乙烯（ＶＬＤＰＥ）与其它ＰＥ的互容性．ＨＤＰＥ／ＶＬＤＰＥ是共晶互容的，以其大量无规部分“溶解”了ＨＤＰＥ的结晶缺陷部分，提高了ＨＤＰＥ的Ｔｃ，Ｔｍ，Ｘｃ，结晶峰半高宽变窄，晶胞参数随组成而有最低值．ＶＬＤＰＥ与ＬＬＤＰＥ结构极为相似，ＤＳＣ及ＷＡＸＤ证明其共混物是共晶相容体系．ＬＤＰＥ／ＶＬＤＰＥ的结晶度符合按组成的计算值，但晶胞参数ａ，ｂ以及晶粒尺寸增大，ＤＳＣ上有分别相应于两组份的两个Ｔｍ；ＶＬＤＰＥ的Ｔｃ，Ｔｍ峰高之和高于按组份的计算值，ＬＤＰＥ的Ｔｍ，Ｔｃ则低于计算值．认为是正如ＬＬＤＰＥ／ＬＤＰＥ，ＬＤＰＥ向充满整个体积的ＶＬＤＰＥ中不断填入，以ＶＬＤＰＥ为晶核而结晶，形成相分离的不相容体系．     

Glass transition and miscibility in blends of two semicrystalline polymers: Poly(aryl ether ketone) and poly(ether ether ketone)

Binary melt‐blended mixtures of two aryl ether ketone polymers (i.e., a new poly(aryl ether ketone) (code name PK99) and poly(ether ether ketone) (PEEK), have been studied. Polymer miscibility in glassy amorphous (or melt) domains has been demonstrated for the binary blend comprising of two aryl‐ether‐ketone‐type semicrystalline polymers. Composition‐dependent, single T_g was observed within full composition range in the PK99/PEEK blends, and the narrow T_g breadth also suggests that the scale of mixing was fine and uniform. To better resolve any possible overlapping T_g's, physical aging was imposed on a comparison set of blend samples for the purpose of improving detectability of overlapped multiple transitions if existing. The result still showed one single T_g. The relative sharp T_g and lack of cloud point transition suggest that the scale of molecular intermixing is good. Phase homogeneity was further confirmed using optical and scanning electron microscopy. The X‐ray diffractograms suggest that isomorphism does not exist in the PK99/PEEK blends and that the crystal forms of the respective polymers remain distinct and unchanged by the miscibility in the amorphous region. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1485–1494, 1999     

ATOMIC FORCE MICROSCOPY STUDIES OF POLYCAPROLACTONE RINGED SPHERULITES*

The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic forcemicroscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found thatthe ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of thespherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite underpolarizing microscope coincided with its surface characteristics. The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface, while the dark rings coincided with the concave rings.     

Effect of the liquid–liquid phase separation on the crystallization behavior of a poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase separation (LLPS) on the crystallization behavior of poly(ethylene‐ran‐vinyl acetate) with a vinyl acetate content of 9.5 wt % (EVA‐H) in the critical composition of a 35/65 (wt/wt) EVA‐H/paraffin wax blend was investigated by small‐angle light and X‐ray scattering methods and rheometry. This blend exhibited an upper critical solution temperature (UCST) of 98°C, and an LLPS was observed between the UCST and the melting point of 88°C for the EVA‐H in the blend. As the duration time in the LLPS region increased before crystallization at 65°C, both the spherulite size and the crystallization rate of the EVA‐H increased, but the degree of the lamellar ordering in the spherulite and the degree of crystallinity of the EVA‐H in the blend decreased. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 707–715, 2000     

Viscoelastic properties and interfacial tension of polystyrene–polyethylene blends

The linear viscoelastic properties of polystyrene polyethylene (PS/PE) blends have been investigated in the molten state. For concentrations of the dispersed phase equal to 30 vol %, the blends exhibited a droplet‐matrix morphology with a volume‐average diameter of 5.5 μm for a 70/30 PS/PE blend at 200 °C and 14.7 μm for a 30/70 PS/PE blend at 230 °C. Enhanced elasticity (G′) for both blends, in the terminal zone, compared to the modulus of the matrix (PS and PE, respectively) was observed. This is related to the deformation of the droplets in the matrix phase and hence to the interfacial forces between the blend components. The results for these uncompatibilized blends are shown to be in agreement with the predictions of the emulsion model of Palierne. These predictions were used to obtain the interfacial tension between PS and PE, which was found to be between 2 and 5 mN/m at 200 °C and 4 ± 1 mN/m at 230 °C. Independent interfacial tension measurements using the breaking‐thread method resulted in a value of 4.7 mN/m and 4.1 mN/m at 200 °C and 230 °C for the respective blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1359–1368, 2000