Performance of hybrid reinforcements in PVC composites. II: Use of surface-modified mica and different cellulosic materials as reinforcements

The effect of the composition of various wood fibers and surface-treated mica as well as different surface treatments of cellulosic materials on the mechanical properties of PVC composites has been evaluated. Cellulosics were surface modified by prior coating with maleic andydride (MA), mixtures of MA and Na-silicate and isocyanate. The filler concentration was fixed at 25 wt%. Both tensile strength and modulus of composities filled solely with mica are superior to those of non-treated wood fiber-filled composities. while the reverse is true for impact strength (except for bagasse-filled composities), ultimate elongation, and tensile toughness. Moreover, the mechanical properties of composities, with the exception of modulus, filled only with mica and/or non-treated wood fibers are inferior to those of unfilled PVC. Compared to non-treated fiber-filled composites, properties improved when surface-modified wood fibers were used alone, or along with mica. Isocyanate-coated wood fibers ranked best with regard to the mechanical properties of the composities. Properties also changed with the change of wood species and compositions of mica and wood fibers. Experimental results indicate good compatibility between surface-treated wood fibers/mica and PVC composities.     

Wetting properties of homopolymers and copolymers of pentafluorostyrene and methylacrylate and homopolymer blends

Polypentafluorostyrene (PPFS), polymethylacrylate (PMA), and poly(pentafluorostyrene-co-methylacrylate), poly(PFS-co-MA) were prepared and the wetting characteristics of polymer blends of PPFS and PMA were compared with that of poly(PFS-co-MA) via contact angle measurements. The critical surface tension of polypentafluorostyrene was found to be 22.6 dyne/cm, which is comparable to the value reported for polytrifluoroethylene (22 dyne/cm). The critical surface tension of poly(PFS-co-MA) is not linearly related to its composition. The polymer blends of PPFS and PMA exhibit significant surface enrichment of the fluoropolymer. The harmonic-mean method¹ was employed to determine surface tensions of these polymers and many known polymers. It is found that the method produces useful surface tension data provided the contact angle values are derived from testing liquids of dissimilar polarity.     

Molecular weight distribution of the graft copolymer comprising mixtures of styrene and acrylamiae on cellulose acetate film by means of gel permeation chromatography

Styrene portion of the radiation-induced graft copolymer comprising styrene and acrylamide was separated by acid hydrolysis and the effects of various grafting parameters (e.g., reaction time, reaction temperature, solvents, monomer composition, etc.) on molecular weight distribution were evaluated by means of gel permeation chromatography. When a single monomer or mixture of two monomers are grafted, the molecular weights is found to increase, but polymer dispersity decreases with the increase of reaction time or reaction temperature except at a higher reaction time due to the continuous enlargment of the growing chain through increased swelling and molecular motion of the trapped radicals. At higher reaction time the degradation of the graft chains lead to lower molecular weight and higher polymer dispersity. Effects of solvents (e.g., methanol, ethanol, and t-butanol) on the molecular weight and molecular weight distribution were discussed on the basis of swelling property and chain transfer constants of the solvents. Styrene-type graft radical being long lived compared to acrylamide type, gave long-chain styrene graft with the increase of styrene content in the reaction mixture. A comparison of the effect of one-and two-component systems on a molecular weight distribution is also discussed.     

Performance of treated hybrid fiber reinforced-thermoplastic composites under extreme conditions. IV. Use of glass fiber and sawdust as hybrid fiber

The mechanical properties and dimensional stability of hardwood aspen in the form of sawdust and surface-treated glass fiber-polystyrene composites were evaluated under various extreme conditions, e.g., variation in the testing temperature (from +25° to ?20°C), exposure to boiling water and heat in an oven at +105°C. The compatibility of wood fiber with glass fiber and with polystyrene improved by precoating the wood fiber with a coupling agent, e.g., 8% isocyanate, 4% silane and polymer. The mechanical properties of the composites, in particular, treated sawdust/glass fiber-filled composites, increased under extreme conditions in comparison with those filled with nontreated sawdust/glass fiber. Under the same conditions, dimensional stability also supports this observation.     

Radiation-induced graft copolymerization of mixtures of styrene and acrylamide onto cellulose acetate. V. Studies on thermal behavior

The thermal behaviors of cellulose acetate, either grafted or ungrafted, were studied. A thermogram of cellulose acetate when grafted with acrylamide is characterized by an endothermic peak at 340°C. If, however, styrene is grafted, the thermogram shows two characteristic exothermic peaks at 330 and 420°C. A thermogram of the mixed graft comprising both acrylamide and styrene, on the other hand, is characterized by only one exothermic peak at 420°C. A consideration of various thermal data indicates that cellulose acetate when grafted is comparatively more stable than when not grafted. Again, styrene is found to be more effective than acrylamide in increasing the stability.     

Studies on the preparation and properties of particle boards made from bagasse and PVC. I: Effects of operating conditions

Under study were the mechanical properties of particle boards comprised of ground sugarcane bagasse, PVC, and poly{methylene (polyphenyl isocyanate)} [PMPPIC]. The effects of different parameters, e.g. mixing temperature, molding conditions - platen temperature, time and pressure, particle size of bagasse, concentration of PVC and PMPPIC, as well as dilution of PMPPIC, on the mechanical properties of the resulting particle boards were also investigated. In general, the properties of particle boards change with the variation of mixing and molding conditions. A mixing temperature of 175°C and molding conditions [platen temperature, 190°C; time, 10 min; and pressure, 3.8 MPa] were believed to be optimal conditions of compounding particle boards. Both the mechanical properties and the density of particle boards of bagasse with a mesh size of 60, improved up to 20 weight % of PVC and 10 weight % of PMPPIC.     

Influence of coupling agents and treatments on the mechanical properties of cellulose fiber–polystyrene composites

Wood fibers of aspen in the form of chemithermomechanical 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.     

Thermoplastic composties of polystyrene: Effect of different wood species on mechanical properties

Both 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 isoeyanate)] (2 and 8 wt % of polymer) was used as a coupling agent. The mechanical 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 π-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.     

Effects of processing variables on the mechanical properties of compression molded polystyrene-wood fiber composites

Optimization of mixing and molding conditions (e.g. temperature, time and pressure) of aspen chemithermomechanical pulp (CTMP)-polystyrene composites was carried out. Compounding conditions showed a substantial effect on the mechanical properties of the composites. The effect of fiber encapsulation with polystyrene on the mechanical properties of the composites was also evaluated. Compared to non-encapsulated ones, the mechanical properties of composites showed superior results when encapsulated CTMP fibers were used. After encapsulation of wood fibers, and optimization of mixing and molding conditions, composites with up to 36% of fiber volume fraction could be incorporated in polystyrene with improved mechanical properties.