B. V. Kokta

Improvement of the mechanical properties of sawdust wood fibre—polystyrene composites by chemical treatment

Abstract The mechanical properties of compression-moulded polystyrenes filled with sawdust wood residue of softwood and hardwood species have been investigated. The tensile modulus at 0.1% strain and the tensile strength, elongation and energy at the yield point are reported. The suitability of sawdust wood residue as a filler for thermoplastics has been tested using two different mesh sizes (20 and 60), as well as by varying the weight percentage of fibres from 10% to 40%. Moreover, to improve the compatibility of the wood fibres with the polymer matrices, different treatments (e.g. graft copolymerization) and coupling agents (e.g. silanes and isocyanates at various concentrations) have also been used. The extent of the improvement in mechanical properties depends on the fibre loading, on the particle size of the fibre, on the concentration and chemical structure of the coupling agents, and on whether special treatments (e.g. coating or grafting of the fibre) are used. The mechanical properties of the composites are improved up to 30% in the case of fibres having a mesh size 60 and when up to 3% of isocyanates was used.

Thermal degradation behavior of cellulose fibers partially esterified with some long chain organic acids

The thermal degradation behavior of cellulose fibers and some fibrous cellulose esters with partial degree of substitution has been studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). Cellulose esters were prepared by heterogeneous esterification in Py/TsCl with unsaturated or saturated long chain organic acids [undecylenic (C11), undecanoic (C11), oleic (C18) and stearic (C18)]. The thermal degradation of cellulose fibers follows a one-step process. The thermal stability of cellulose esters is inferior to that of unmodified cellulose fibers and the thermograms show a two-step degradation process, probably controlled by crosslinking reactions, which occur during thermal decomposition. Exothermic peaks in the DSC thermograms are also an indication of such reactions. Kinetic parameters such as the activation energy E, order of decomposition n, and frequency factor Z were obtained following the Friedman method. The cellulose sample followed first order of decomposition, however for cellulose esters higher orders were observed.

Use of Wood Flour as Filler in Polypropylene: Studies on Mechanical Properties

Abstract Mechanical properties of polypropylene (PP) filled with wood flour was studied. To improve adhesion at the interface, different surface treatments of the fiber were carried out. Polymethylene polyphenylisocyanate (PMPPIC) and silane coupling agents (silane A-172, A-174, and A-1100) were used to pretreat the fiber before it was introduced into the polymer. Increase in tensile strength, with fiber concentration, was found in PP filled with PMPPIC pretreated wood flour. Elastic modulus was unaffected by fiber treatment. Izod-impact strength decreased with increased filler level in the composite.

Composites of Polyvinyl Chloride-Wood Fibers. I. Effect of Isocyanate as a Bonding Agent

Abstract Various parameters concerning the performance of isocyanate as a coupling agent have been discovered. Greater premixing time (e.g., 20 min) leads to an improvement in the mechanical properties of the composites. the isocyanate solution is more efficient in comparison with undiluted isocyanate. Moreover, the chemical structure of isocyanate, which provides a better interaction with thermoplastics, results in superior properties. the reactivity of different isocyanates decreases in the following order: PMPPIC, TDIC, HMDIC, EIC. Again, isocyanate can act as a promoter or as an inhibitor, depending on the concentration of isocyanate used. For example, with a moderate concentration, it promotes maximum mechanical properties, while with a higher concentration, mechanical properties deteriorate. In addition, the nature of the pulp (e.g., CTMP, cotton, or sawdust) and fiber loading percentage as well as different grades of polymer supplied by different companies also play an important role in the mechani...

The Influence of Coupling Agents On Mechanical Properties of Composites Containing Cellulosic Fillers

Abstract Three different cellulosic fibers-a mechanical pulp, wood flour, and cellulose pulp-were used as filler in high-density polyethylene (HDPE). the addition of wood fiber in HDPE increased the stiffness of the composites while the tensile strength decreased. to improve the adhesion between the filler and the polymer matrix, wood fibers were pretreated with a silane coupling agent/polyisocyanate before compounding with the polymer. Tensile strength increased from 18.5 MPa (untreated fiber) to 35.2 MPa in isocyanate-treated fiber composites. Analysis of the filler cost/performance showed the advantage of wood fiber over glass fiber and mica.

Fibrous long-chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy, solid-state CP/MAS 13C-NMR, and X-ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1- or 2-h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid-state CP/MAS 13C-NMR (75.3 MHz). X-ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X-ray spectra or the unassigned C-4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X-ray diffraction data (4.1 nm).

Interfacial adhesion of lignocellulosic materials in polymer composites: an overview

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 ...

Structure-Property Relationships of Wood Fiber-Filled Polypropylene Composite

Abstract The effects of the addition of interface modifiers on the structure and properties of wood fiber-filled polypropylene (PP) have been studied. Although an increase in the wood fiber loading reduces the overall cost of composites, the mechanical properties of such composites are very poor in the absence of a suitable interface modifier. The poor mechanical and thermal properties of the unmodified composite are attributed to increased heterogeneity induced in the system with increased concentration of wood fiber. A significant improvement in tensile strength and thermal resistance of these composites in the presence of a suitable interface modifier such as maleated polypropylene, itaconic anhydride, or bismaleimide-modified polypropylene is due to the improved dispersity of wood fibers in the polypropylene matrix as well as to the development of a stable interface effected by chemical interaction. In general, all modifiers are found to affect the crystallinity of PP in composites, and an improvement...

Improving adhesion of wood fiber with polystyrene by the chemical treatment of fiber with a coupling agent and the influence on the mechanical properties of composites

—The mechanical properties of polystyrene filled with chemithermomechanical pulp and wood residues of softwood and hardwood species, which were precoated with phthalic anhydride and various polymers, e.g. polystyrene and PVC, have been investigated. The extent of improvement in the mechanical properties of the composite materials depends on the coating composition, the concentration of phthalic anhydride, the nature of the coated polymers, as well as the concentration of fiber, the nature of the wood species, and the nature of the pulps. Experimental results indicate that phthalic anhydride acts as a coupling agent, but when its performance was compared to that of poly[methylene (polyphenyl isocynate)], it seemed inferior to the latter.

Polypropylene-Wood Fiber Composites: Effect of Fiber Treatment on Mechanical Properties

Abstract Polypropylene (PP) was reinforced with different wood fibers, chemithermomechani-cal (CTMP) aspen and commercial pulps (Tempure and Temalfa-A). Various chemical treatments on the fiber was carried out to improve the bonding at the interface. Fibres coated with Silane coupling agents Silane A-172 and A-174 (with vinyl and methacryloxy functional groups respectively) upon reinforcement showed poor tensile strength. PP filled with Pre-coated fibers containing maleated propylene wax, polymer and polymethylene polyphenyl isocyanate produced higher tensile strength and modulus. The use of dicummyl peroxide and cummine hydro peroxide as initiators during the coating of the fiber was not effective. Polypropylene reinforced with fibers of lower mesh size gave better tensile properties.