A new "aggregate" model for ionomers is presented. The model is similar to the "homogeneous" model in that the acid aggregate distribution is assumed to be homogeneous and similar to the "cluster" model in that acid 1 groups are assumed to aggregate. The aggregate model, however, differs from the other models in that the degree of aggregation is low and affected by carboxyl group concentration and the presence of polar diluent. The aggregates are much smaller than the clusters previously theorized. New data obtained by wide and small-angle X-ray scattering and differential scanning calorimetry are presented. These techniques are used to study the X-ray peaks attributed to ionic clusters. Changes in the X-ray scattering behavior of ionomers with composition are interpreted in terms of an increase in the number of carboxyl groups per scattering site. The aggregation increases from dimers to trimers to tetramers up to septimers as the acid content in the copolymer increases. Plasticization with water is shown to further increase the extent of carboxyl group aggregation.

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Although lignocellulosic, fiber‐thermoplastics composites have been used for several decades, recent economic and environmental advantages have resulted in significant commercial interest in the use of these fibers for several applications. Kenaf is a fast growing annual growth plant that is harvested for its bast fibers. These fibers have excellent specific properties and have potential to be outstanding reinforcing fillers in plastics. This paper reports the structure‐property relationships of kenaf fiber reinforced polypropylene (PP) and its impact copolymers. The use of maleated polypropylenes (MAPP) is important to improve the compatibility between the fiber and matrix. A significant improvement in impact strengths was observed when the MAPP was used in the composites. Results also indicate that the impact copolymer blends with coupling agent have better high temperature moduli and lower creep compliance than the uncoupled systems. The coupling agent also changes the crystallization and melting behavior of these blends. Because of the better adhesion between the polymer molecules and kenaf fibers, the coupled samples have more restricted molecules than the uncoupled blends. As a result, the crystallization of the coupled high molecular weight blends is slower than the uncoupled blends, resulting in a lower crystallization temperature (Tc) and reduced crystallinity. For the lower molecular weight blends, the coupling agent enhances the crystallization of polymer matrix and results in a higher crystallization temperature and increased crystallinity of the coupled blend. The coupled blends also have more defects in the polymer crystals, and the crystallinity of coupled blends is also lower than the uncoupled blends. This could explain the lower melting temperatures of the coupled samples as compared to uncoupled samples.

This study aims to explore the processing benefits and property improvements of combining nanocomposites with microcellular injection molding. The microcellular nanocomposite processing was performed on an injection‐molding machine equipped with a commercially available supercritical fluid (SCF) system. The molded samples produced based on the Design of Experiments (DOE) matrices were subjected to tensile testing, impact testing, Dynamic Mechanical Analysis (DMA), and Scanning Electron Microscope (SEM) analyses. Molding conditions and nano‐clays have been found to have profound effects on the cell structures and mechanical properties of polyamide‐6 (PA‐6) base resin and nanocomposite samples. The results show that microcellular nanocomposite samples exhibit smaller cell size and uniform cell distribution as well as higher tensile strength compared to the corresponding base PA‐6 microcellular samples. Among the molding parameters studied, shot size has the most significant effect on cell size, cell density, and tensile strength. Fractographic study reveals evidence of different modes of failure and different regions of fractured structure depending on the molding conditions. Polym. Eng. Sci. 44:673–686, 2004. © 2004 Society of Plastics Engineers.

SYNOPSISThe amount of research on lignocellulosic /thermoplastic composites has increased dramatically. Little attention, however, has been directed towards the subject of crystallinity at the interface (interphase). Optical microscopy and differential scanning calorimetry were used in this work to study crystallinity in the cellulose/polypropylene system. The results verify that cellulose acts as a nucleating agent for polypropylene, producing a transcrystalline region around the fiber. Treatment of the fibers with alkyl ketene dimer ( AKD) , alkenyl succinic anhydride ( ASA) , or stearic acid, inactivates the surface features responsible for transcrystallinity. These treatments also affect the overall degree of crystallinity of the sample. Morphological features, resulting from a transcrystalline or nontranscrystalline interphase, may have a significant effect on mechanical properties. A possible mechanism for the appearance of transcrystallinity involving crystal structure matching is also proposed.

The interest in lignocellulosic fiber composites has been growing in recent years because of their high specific properties. In this work, a new technique was used to prepare specimen to observe the transcrystalline zones in kenaf fiber-polypropylene composites. A maleated polypropylene (MAPP) coupling agent was used to improve the stress-transfer efficiency in the composites. Transcrystallinity was observed for both the uncoupled and coupled composites, although the rate of growth was higher for the coupled composites. Dynamic mechanical spectroscopy was used to observe the relaxations of the composites. The peak temperature of the β-relaxation, associated with the glass-rubber transition of the amorphous molecules, of the coupled composites was higher than that of the uncoupled composites. Restricted molecular mobility due to covalent interactions between the MAPP and the lignocellulosic surface may account for the shift to higher temperatures. It appears that during compounding the extractives sheared from the fiber surface is an important factor in determining the β-relaxation of these composites. The intensities of the α-transition, related to molecular mobility associated with the presence of crystals, is proportional to the fiber volume fraction. Thus it is possible that the molecules responsible for the α-transition are predominantly in the transcrystalline zone. These 'rigid' amorphous molecules in the transcrystalline zone do play a role in composite behavior and need to be considered when tailoring interphases.

The relative influence of ball milling for various time periods on the course of enzymatic and dilute acid hydrolysis was investigated. The response of enzymatic hydrolysis to the extent of milling was quite dramatic. Cotton linters pulp was totally hydrolyzed in 10 days with 60 min of milling. The carbohydrates of red oak were 93% converted to sugar in the same time after 240 min of milling. It appears that, with sufficient milling, the carbohydrates of the three lignocelluloses investigated can be made almost totally accessible to enzymatic hydrolysis. Vibratory milling also yields substantial increases in the rates of dilute acid hydrolysis of all four substrates, nearly nine-fold for the cotton linters pulp and about five-fold for the three lignocelluloses. Thus vibratory milling represents an experimentally effective pretreatment.ignin and cellulose crystallinity are major deterrents to the chemical, enzymatic, and microbiological conversion of lignocellulosic residues to useful products. Lignin restricts enzymatic and microbiological access to the cellulose. Crystallinity restricts the rate of all three modes of attack on the cellulose. Thus if we are ever to make full use of the carbohydrate values contained in the many millions of tons of currently unused lignocellulosics generated in this country each year, some form of pretreatment must be employed to alter the fine structure of cellulose as well as disrupt or open up the lignin-carbohydrate complex. 1 Maintained at Madison, WI, in cooperation with the University of Wisconsin. This chapter not subject to U.S.

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