SynopsisLinear low density polyethylene (LLDPE) was reinforced with different wood fibers, aspen chemithermomechanical pulp (bleached and unbleached), and other commercial wood pulps. Silane coupling agents A-172, A-174, A-1100, and polymethylene polyphenyl isocyanate were used to improve the bonding between the fiber and matrix. LLDPE filled with pretreated wood fiber produced a significant improvement in tensile strength and modulus. Comparison of tensile and impact properties of wood fiber composites with mica &nd glass fiber composites shows the potential advantage (in terms of material cost and specific properties) of wood fiber as a reinforcement.

SynopsisWood fibers of aspen in the form of chemithennomechanical pulp (CTMP) and Tembec 6816 have been used as reinforcing fillers in different varieties of polystyrene. The tensile strength, elongation, and energy at maximum point, as well as tensile modulus at 0.1% strain is reported. Also revealed is the optimum condition of compression molding. The influence of different coupling agents, such as poly[methylene(polyphenyl isocyanate)], silanes (A-172, A-174, A-1100), and grating on the mechanical properties of composites is discussed. The extent of increase in mechanical properties depends on the weight percentage of fibers, the concentration of coupling agents, and the grafting level (add-on %). Coating followed by an isocyanate treatment appears to be the best treatment. In addition, the isocyanate treatment and grafting are superior to the silane treatment. Experimental results are explained on the basis of possible interactions among cellulose fiber-coupling agent-polymer in the interfacial area.

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Cellulosic materials have long been used as cost-cutting fillers in the plastic industry. Among the various factors which determine the final performance of the composite materials depend, to a large extent, on the adhesion between the polymer matrix and the reinforcements, and, therefore, on the quality of the interface. In fact, the majority of cellulosic raw materials are lignocellulosics of different polarity to plastics, and due to this divergent behavior, the adhesion between cellulosic materials and polymer matrices is very poor. However, a sufficient degree of interaction or adhesion between the surface of the cellulosic materials and matrix resin is usually desired to achieve an optimum performance of the end-product. In many cases surface modification of the cellulosics or the matrix resins, using various additives, vinyl monomers, or coupling agents, are considered to be essential to achieve this goal.The present paper surveys research work published in this field with special emphasis on the cellulosic materials' surface chemistry, morphology, as well as interfacial properties of the composites in order to elucidate the role of surface treatments. In order to elucidate the mechanism of interaction on molecular level, it is necessary to employ various techniques, such as spectroscopy that can measure surface events. In fact, the complexity of the interphase region requires a variety of characterization methods for the thorough understanding of the physical and chemical nature of this region. Moreover, a proper combination of different techniques is necessary to provide a true picture of the interphase.

SynopsisBoth softwood (spruce) and hardwood (aspen and birch) species in the form of different pulps (e.g., sawdust, chemithermomechanical pulp, explosion pulp and OPCO pulp) have been used (10-40 wt% composite) as reinforcing fillers for thermoplastic composites of polystyrene. Mechanical properties, are examined, e.g., tensile modulus, tensile strength at maximum point, and the corresponding elongation and energy as well as impact strength of compression molded composites. To improve the compatability of wood fibers which are hydrophilic and the polymer matrix which is hydrophobic, poly[methylene(polyphenyl isocyanate] (2 and 8 wt% of polymer) was used as a coupling agent. The mechanic,al properties of the treated composites are improved up to 30% in fiber content whereas a downward trend for untreated composites was observed when an increase in fiber content occurred. The overall improvements in mechanical properties due to the addition of isocyanate can be explained by the linkage of isocyanate molecules with fiber matrix through the chain of covalent bonds and the interaction of .n-electrons of benzene rings of polystyrene as well as isocyanate. As a result, poly[methylene(polyphenyl isocyanate)] forms a bridge between fiber and polymer on the interfaces. This result is instrumental for efficient stress transfer between cellulose fibers and thermoplastics. The performance of different pulps of various wood species as reinforcing fillers for thermoplastic composites is also examined.