Wood Polypropylene Composites Research Articles

Flammability of wood–polypropylene composites

Addition of wood particles to polymers can cause a change of properties of the composites which depends on features of lignocellulosic materials and those of polymers. It is also observed in the flammability characteristics of the composites. In this work, the flammability of polypropylene composites with pine wood particles obtained by extrusion and press moulding was analyzed. The amount of wood particles was 50%. Polymers with various melt flow index (MFI) were used (Malen F-401, PP HY-202 and Malen S-702). The samples were tested using Cone Calorimeter at heat flux of 35 kW/m 2. Heat release rate (HRR) curves of composites show that thermal decomposition depends on the kind of polypropylene used. In the presence of PP HY-202 and Malen S-702, the flammability characteristic is similar to that of lignocellulosic materials, in contrast to composites with matrices prepared from Malen F-401. The observed phenomenon is interpreted in terms of the wettability of particles of pine wood by polymers of varying melt viscosity.

Resistance of polypropylene-wood composites to fungi

In the present study, the composites of polypropylene and wood were prepared. The experimental material comprised two most common Polish timber species pine wood (Pinus sylvestris L.) as a softwood species and oak wood (Quercus sp.) as a hardwood species. The size of wood sawdust ranged from 0.5 to 1.0 mm. Two types of lignocellulosic materials were used in the experiments described: wood without any previous chemical treatment and wood after its mercerization (i.e. activated with NaOH). In addition the polypropylene-wood composite containing a block copolymer, i.e. styrene¯ethylene¯butylene¯styrene (SEBS) was also obtained. The objective of this study was to evaluate the resistance of different kinds of polypropylene-wood composites to fungal decay. Weight losses and temporary tensile strength of composite samples after the mycological test were determined.

On engineering of properties of wood-polypropylene composite

New materials based on wood have the advantage in the sense that their properties can be engineered so as to correspond to user demands. The properties which can be engineered are those relating both to their utilisation and machining, in particular - the tensile strength, elongation at break, modulus of elasticity and impact resistance. The research at the Faculty of Forestry and "Hipol" Chemical Industry related to the new type of wood-polypropylene composite. The content of wood filler was varied in the range between 40% and 70% mass contents of beech wood flour. After the highest tensile strength at 50% of filler content was determined, the effect of the wood filler origin was also examined at this content value. Therefore, wood flour of beech, poplar, acetylated pine and the waste MDF was used. The influence of the composition of the wood filler (beech combined with MDF, poplar and acetylated pine) in comparison with pure polypropylene matrix was also examined, as well as the effect of the type of coupling agent. Hopefully, the results obtained in this study might serve as the initial data for production of easily machined high-strength composites.

Improvement of interfacial adhesion between wood and polypropylene in wood–polypropylene composites

N-vinylformamide-grafted polypropylene (VFPP) was successfully synthesized through a free radical grafting reaction. Both polymeric methylene diphenyl diisocyanate (PMDI) and VFPP were effective compatibilizers for increasing both the strength and stiffness of the resulting wood–PP (polypropylene) composites. Both the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the resulting wood–PP composites were further increased when PMDI and VFPP were used together as an integrated compatibilizer system. This new PMDI-VFPP compatibilizer system was comparable to maleic-anhydride-grafted polypropylene in terms of enhancing the strength and stiffness of the wood–PP composites. Study of the fractured surfaces of the wood–PP composites with scanning electron microscopy revealed that this new PMDI-VFPP compatibilizer system greatly improved the interfacial adhesion between wood and PP. This PMDI-VFPP compatibilizer system also greatly reduced the water absorption of the resulting wood–PP composites. In this PMDI-VFPP compatibilizer system, PMDI is proposed to function as a wood-binding domain and VFPP to function as a PP-binding domain. PMDI reacted with the amide group in VFPP, thus forming covalent linkages between PMDI and VFPP.

Effect of extractives on the flexural properties of wood/plastic composites

This study investigated the effect of extractives in wood flour on the mechanical properties of wood-polypropylene (PP) composites. Three different solvents, acetone/water, dioxane/water and benzene/ethanol, were used to remove extractives in both pine and Douglas fir wood flour. X-ray photoelectron spectroscopy (XPS) confirmed that extraction resulted in a change in the surface composition of the wood flour. Differential scanning calorimetry showed no changes in the percent crystallinity of the PP matrix in the wood-PP composites and optical microscopy showed no detectable changes in PP spherulite size or shape between filled PP containing extracted and unextracted wood flour. A large increase in the strength of pine flour-PP composites was observed upon removal of extractives from pine flour. The Douglas fir flour-PP composites showed a smaller, but statistically significant, increase in strength upon removal of extractives, with the exception of the dioxane/water extracted Douglas fir. Significant differences were also observed in stiffness between extracted wood-PP and unextracted wood-PP composites with the exception of the dioxane/water extracted Douglas fir, which was not significantly different from the control.

Interaction between coupling agent and lubricants in wood–polypropylene composites

Commercially available additives and a copolymer system were investigated for their impact on composite morphology and crystallization kinetics. This research focuses on the influence of the coupling agent and lubricants on the crystallization of polypropylene in the bulk and interphase regions and the subsequent spatial distribution of the additives. Differential scanning calorimetry and polarized light microscopy were used to determine kinetic parameters for the crystallization process of the polypropylene in the bulk composite melt and at the wood–polypropylene interface. No differences were found in the kinetics of the crystal formation nucleated on the wood surface and in the bulk polymer by polarized microscopy. Using microbeam Fourier transform infrared spectroscopy, the spatial distribution of lubricants and coupling agents were delineated. Lubricants that tended to interfere with wood–polypropylene coupling dispersed throughout the transcrystalline region around the fiber. In contrast, lubricants with lower degree of interference appeared to be phase separated in the amorphous regions between the crystals. These findings are consistent with calorimetric results that show differences in the quality of the crystals formed by the neat polypropylene.

Microcellular Wood Fibre Reinforced Polypropylene Composites in an Injection Moulding Process

Microcellular foams of polypropylene containing wood fibres, cell sizes on the order of 10 to 50 μm were produced by injection moulding. The relationships of processing/structure/property were investigated for wood fibre-thermoplastics composites foaming with a chemical blowing agent. Wood polypropylene composites (WPC) of different wood content (30%, 40%, 50% and 60% by weight) were prepared using maleic anhydride-polypropylene copolymer (5% relative to the wood fibre content) as a coupling agent. Measurement of density, cell size, void content, tensile and flexural test of the prepared WPC were carried out. The shape and distribution of the voids were investigated by optical photo examination of longitudinal sections of specimens, using a polishing technique and reflected light microscopy. The density of foamed composites decreased about 24%. The cell morphology and foam properties showed improvement when the coupling agent was added. Water absorption and scanning electron microscope of the composites also investigated.

Physico-mechanical studies of wood fiber reinforced composites

Wood polypropylene composites (WPC) of different compositions (30, 40, and 50%) have been prepared using maleic anhydride–polypropylene copolymer of different percentage (5 and 10% relative to their wood fiber content). Tensile, flexural, fracture toughness, and impact test of the prepared WPC were carried out. From the results, it is observed that the hard wood fiber–polypropylene composites, by using maleated polypropylene (MAH-PP), show comparatively better performance to soft wood fiber–polypropylene composites. Tensile strength and charpy impact strength have been increased to a maximum of 50 and 20%, respectively. The damping index has been decreased by 60% when 10% of MAH-PP has been used. Water absorption and scanning electron microscopy of the composites are also investigated.

Polypropylene Crystallization on Maleated Polypropylene-Treated Wood Surfaces: Effects on Interfacial Adhesion in Wood Polypropylene Composites

AbstractPolypropylene (PP)-wood veneer laminates were used as a model system to investigate adhesion in wood-polypropylene composites. Wood veneers were treated with maleated polypropylene waxes (MA-PP). PP films were then compression molded to the wood surfaces and peel forces were measured.Low MA-PP treatment levels increased the peel adhesion over that for untreated surfaces. High MA-PP treatment levels decreased the peel adhesion and intermediate MA-PP levels had no effect on the peel adhesion. Microscopy of the fracture surfaces indicated PP penetration into lumens in both treated and untreated wood veneer. Untreated surfaces also exhibited PP penetration into pits and intercellular spaces, while treated surfaces exhibited only hindered penetration on this scale. The penetrated PP formed tendrils during fracture. DSC of PP on wood and cellulose surfaces showed higher PP crystallization temperatures on untreated surfaces than on treated surfaces.