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SYNOPSISThe effect of various corona treatment conditions on the mechanical properties of cellulose fibers/polypropylene composites was studied. The cellulose fibers and polypropylene were modified using a wide range of corona treatment levels and concentrations of oxygen. The treatment level of the fibers was evaluated using the electrical conductance of their aqueous suspensions. The mechanical properties of composites obtained from different combinations of treated or untreated cellulose fibers and polypropylene were characterized by tensile stress-strain measurements; they improved substantially when either the cellulose fibers alone or both components were treated, although composites made from untreated cellulose fibers and treated polypropylene showed a relatively small improvement. The results obtained indicate that dispersive forces are mostly responsible for the enhanced adhesion. The relationship between the electrical conductance of the fibers, the mechanical properties, and the mechanism of improved adhesion is discussed.

A systematic study of the effect of surface pretreatment of cellulosic fibers and the processing time and temperature on the mechanical properties of the cellulose‐containing polypropylene was undertaken. Using non‐treated fibers, the elastic modulus increased gradually with the cellulose content, typically doubling its value at 30 phr fiber content. Treatment of fibers with coupling agent improves significantly the interfacial adhesion and therefore the mechanical properties of composite. Scanning electron micrographs reveal that the shear stress is sufficiently high to break and delaminate the cellulosic fibers. Addition of maleic anhydride modified polypropylene also improves the properties of resulting composites.

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The rheological behavior of wood fiber/polyethylene composites made of corona treated constituents was investigated. Corona treatment of one or both of the constituents resulted in decreased melt viscosities relative to compounds containing untreated materials. The reduction of melt viscosity may originate from low molecular weight moieties formed on the surfaces of both polyethylene and cellulose during corona treatment. These may act as lubricants at interfaces. Also it was found that the corona treatment of fibers leads to higher packing volumes; this may result from a reduction in fiber length when treated fibers are processed under high shear conditions. As a result these fibers perturb the normal flow pattern in the melt to a lesser degree than the longer fibers of untreated cellulose.

SynopsisThe strength properties of composites made of untreated cellulose fibers and linear low density polyethylene were investigated as a function of processing parameters. Studies have shown that the strength properties of composites increase with processing time and temperature. The increase in strength is accompanied by the appearance of new infrared absorption bands at 1718 and 1735 cm-'. A linear relationship between the absorbance and yield strength of composites indicates that oxidation, possibly directly at interfaces, takes place and enhances adhesion between the cellulose and polyethylene.

The effect of corona treating the surfaces of components on tensile properties of wood fiber linear low-density polyethylene composites has been investigated. Corona treatment results in a significant increase in strength properties of the composites. Yield stress increases after treatment of one or both of the composite components. Pronounced improvement in ductility has been observed for composites containing 15 to 30% of the corona modified fiber. Relevant mechanisms involved are discussed.

SynopsisThe present study reports results on the processing and mechanical properties of composites modified by the addition of dicumyl peroxide (DCP). The addition of minute amounts of peroxide to the cellulose/polymer system during processing has been show,n to significantly improve the physical properties of composites. SEM micrographs of fracture surfaces of the peroxide modified composites reveal direct grafting of polyethylene onto cellulose fibers. The existence of a critical peroxide concentration indicates that the grafting reactions terminate when cellulose surfaces are no longer accessible. Possible mechanisms involved are discussed.