John J. Balatinecz

Surface modification and adhesion mechanisms in woodfiber-polypropylene composites

The interfacial adhesion between wood fiber and thermoplastic matrix polymer plays an important role in determining the performance of wood-polymer composites. The objectives of this research were to elucidate the interaction between the anhydride groups of maleated polypropylene (MAPP) and hydroxyl groups of wood fiber, and to clarify the mechanisms responsible for the interfacial adhesion between wood fiber and polypropylene matrix. The modification techniques used were bulk treatment in a thermokinetic reactive processor and solution coating in xylene. FT-IR was used to identify the nature of bonds between wood fiber and MAPP. IGC and wood veneer pull-out test was used to estimate the interfacial adhesion. Mechanical properties of injection molded woodfiber-polypropylene composites were also determined and compared with the results of esterification reaction and interfacial adhesion tests. Confocal Microscopy was employed to observe the morphology at the wood fiber-polypropylene interface, and the dispersion and orientation of wood fiber in the polypropylene matrix, respectively. The effectiveness of MAPP to improve the mechanical properties (particularly the tensile strength) of the composites was attributed to the compatibilization effect which is accomplished by reducing the total wood fiber surface free energy, improving the polymer matrix impregnation, improving fiber dispersion, improving fiber orientation, and enhancing the interfacial adhesion through mechanical interlocking. There was no conclusive evidence of the effects of ester links on the mechanical properties of the composites.

Diffuse reflectance Fourier transform infrared spectra of wood fibers treated with maleated polypropylenes

The esterification reaction between wood fibers and maleated polypropylenes was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as catalyst. The reaction between wood fibers and pure maleic anhydride was also investigated. The appearance of an infrared absorption band near 1730 cm−1 indicated that maleated polypropylene chemically reacted by esterification with bleached Kraft cellulose. However, no direct evidence of an esterification reaction was obtained between thermomechanical pulp and maleated polypropylene. The Fourier transform infrared (FTIR) studies showed also that both bleached Kraft cellulose and thermomechanical pulp reacted with maleic anhydride with the formation of ester links.

Surface characterization of esterified cellulosic fibers by XPS and FTIR Spectroscopy

Abstract X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy techniques were used to study the surface chemical compositions of cellulosic fibers before and after treatments. The fibers were treated with phthalic anhydride and maleated polypropylene for surface modifications. Both XPS and FTIR spectroscopy analysis indicated that chemical bonds between hydroxyl groups of cellulosic fibers and anhydride moieties of phthalic anhydride and maleated polypropylene have occurred through esterification reaction. These chemical reagents have been added to the surface of cellulosic fibers in the form of monoester, i.e., the formation of esterified cellulosic fibers bearing a pendent carboxylic group.

Creep fatigue in engineered wood fiber and plastic compositions

Creep behaviour of unmodified and functionally modified thermoplastic-wood fibre composites was studied. For PVC, PE and PP-based composites creep is strongly dependent on the amount of load, time and temperature. A small rise in the temperature above ambient temperature increased creep significantly for PVC-woodfiber composites. Instantaneous creep resistance of woodfibre-filled PP is higher than that of PE-based composites. PP and PE-based wood composites were modified with maleic and maleimide compounds. Maleic or maleimide modification of woodfibre improved transient creep behaviour of PP-woodfibre composite but it did not show practically any effect on instantaneous creep. A mathematical model has been proposed to predict creep behaviour of PVC, PP an PE-based wood fiber composites.

X-ray photoelectron spectroscopy study of silane-treated newsprint-fibers

Abstract The nature of adhesion in multicomponent materials such as cellulosic fibers/thermoplastic composites is strongly dependent on the surface properties of the components. X-ray Photoelectron Spectroscopy (XPS) was used to characterize the surfaces of untreated and treated newsprint-fibers. Gamma-aminopropyltriethoxysilane and dichlorodiethylsilane were used for the surface modification of the fibers. The XPS analysis indicated that coupling between the silanes and the newsprint-fibers has occurred, and that silanols were adsorbed to the surface of newsprint-fibers by two different mechanisms: (1) an ether linkage between the silanols and the hydroxyl groups of the fibers and (2) a hydrogen bonding between the amine and the hydroxyl groups of the fibers. The formation of the hydrogen bonding was evidenced by the two observed amino states, i.e., a covalent non-protonated form and an ionic protonated form.

Characterization of microcellular foamed PVC/cellulosic-fibre composites

A microcellular plastic is a foamed polymer of a cell size in the range of 0.1 to 10 μm and a cell density in the range of 109 to 1015 cells/cm3. Typically, microcellular plastics have been shown to possess superior impact strength, toughness, and fatigue life to solid polymers. Polymer/cellulosic-fibre composites make use of cellulosic-fibres as a reinforcing filler in the polymer matrix and are known to be advantageous over the neat polymers in terms of the material cost and some mechanical properties such as stiffness and specific strength. These polymer/cellulosic-fibre composites are microcellular processed to create a new class of materials with unique properties. In this paper, the feasibility of the production of microcellular PVC/cellulosic-fibre composites and the effect of the fibre content on the cell morphology are studied. Particular emphasis is given to the fibre surface treatment to investigate its effect on the microcellular morphology. Each step of microcellular PVC/cellulosic-fibre composite processing is addressed including the treatment of the cellulosic-fibre surface, the manufacture of the composite by the mixing of PVC and cellulosic-fibre, the saturation of the composite with gas, and the bubble nucleation and growth. The preliminary experimental results indicate that the surface modification of cellulosic-fibre plays a strong role in determining the interface between the polymer and fibre as well as the cellular morphology of the foamed composites.

Effects of Impact Modification on the Mechanical Properties of Wood-Fiber Thermoplastic Composites with High Impact Polypropylene (HIPP)

This paper reports on the effects of impact modification on the mechanical properties of wood-fiber thermoplastic composites with high-impact polypropylene (HIPP). Homo polypropylene (PP) was modified through its melt blending with HIPP to obtain an inherently tough matrix resin for PP/wood-fiber composites. The resin modification improved the impact strength of the composites, while it reduced the stiffness and strength properties acquired by the addition of wood-fibers. The requirements of plane strain fracture toughness were not satisfied in this study. In order to compensate the nonplane strain fracture toughness, the specimen strength ratio was used as a comparative measure of fracture toughness. The strength ratio depended on impact modifier levels as well as on wood-fiber concentrations. The work of fracture measured as the area under the load-displacement curve increased with impact modifier levels except at 40% wood-fiber concentration. Microstructural probing showed a degree of wood-fiber alignment in the skin and core of injection-molded specimens and provided some insight into the slight increase in the impact strength of composites.

X-ray photoelectron spectroscopy of maleated polypropylene treated wood fibers in a high-intensity thermokinetic mixer

Summary An XPS (X-ray Photoelectron Spectroscopy), also known as ESCA (Electron Spectroscopy for Chemical Analysis) study of wood fiber treated with maleated polypropylene was performed to obtain information on the chemical nature of wood fiber before and after treatment. Wood fiber was treated in a high-intensity thermokinetic mixer with maleated polypropylene at different loading level (relative to wood fiber weight). The XPS results showed that the treatment of maleated polypropylene increased the hydrocarbon concentration of wood fiber, as indicated by the decrease in oxygen-carbon ratio, and the continuous increase of the relative intensity of the component C1 in C1s signal. Based on these values, higher molecular weight maleated polypropylene produced more hydrophobic wood fiber surface than lower molecular weight maleated polypropylene. The decrease in C4 carbon type in C1s signal after treatment suggested that the esterification reaction between wood fiber and maleated polypropylene had not ocurred under the experimental conditions used in this study.

Durability of Wood Flour-Thermoplastic Composites under Extreme Environmental Conditions and Fungal Exposure

Abstract The main purpose of this research work was to investigate the response of wood flour reinforced polyethylene composites to 2 hours water boiling, five complete boiling and freezing cycles and fungal (Gloeophyllumm Traebum/Brown-rot fungus) exposure. Five composite formulations were manufactured and analyzed (0, 50, 60, 70 and copper carbonate treated 60% wood flour/polyethylene composites). The results showed that wood flour loading decreased the resistance of the composites to moisture and fungal environment. The exposure of the composites to 2 hours water boiling and five complete boiling and freezing cycles caused serious damage to the interfacial adhesion between wood flour and polyethylene matrix due to contraction and swelling stresses developed during cyclic exposure. The addition of 1 percent copper carbonate salt during compounding of wood flour and polyethylene prevented the colonization and proliferation of fungus on the surface of the composites, but had a negative effect on the water uptake and flexural properties of the composites.

X-ray photoelectron spectroscopy of lignocellulosic materials treated with maleated polypropylenes

Abstract The esterification reaction between lignocellulosic materials (ALCELL lignin and Bleached kraft cellulose) and maleated polypropylenes (graft copolymerization of maleic anhydride into polypropylene chains) was investigated. The reaction was conducted in a reactor in the presence of xylene used as a solvent and sodium hypophosphite as a catalyst. The reaction between lignocellulosic materials and pure maleic anhydride was also conducted to determine the effect of the long polypropylene chains on the formation of ester bonds. The XPS studies of maleated bleached kraft cellulose showed the emergence of C4 carbon type on high resolution spectra, which was related to ester carbonyl functionality formed by esterification reaction. No evidence of esterification was observed between ALCELL lignin and maleated polypropylenes. The XPS studies demonstrated that both ALCELL lignin and bleached kraft cellulose chemically react with maleic anhydride with the formation of ester bonds.