Poly composites with wood

For PVC composites, used in housing and in the automobile industry, no coupling agent is used because PVC is rather polar and compatible with wood fibres. Some research has been done and the positive effect of aminosilanes (Kokta etal., 1990a) and poly(methylene(phenyl isocyanate)) (Kokta el al., 1990b) has been demonstrated. 

Thus by the use of Wood s approximation we were able to construct a complete 7 /composition curve for the polyfisobutylene-co- -pinene) system. In view of the experimental difficulties in obtaining the Tg for poiy( -pinene), the accuracy of the dot is questionable beyond V2 = 63 volume% ie., above 63 volume% pinene in the copolymer. Howewr, in the range from 0 to 63 volume% /3-pinene, the curve is considered to be accurate and, importantly, reveals that useful rubbery poly(isobutylene-co-j3 pinene) could be made with up to about 28 vohime% pinene, re, to a Tg of —40 °C. In agreement with cnir spectroscopic and reactivity ratio studies, the (admittedly somewhat limited) applicability of Eq. (1) developed for random copolymers also suggests a statistically random copdymer structure for our poly(isobutylene-co- pinene) products. 

Figure 38-16. Textile composites paper from pine wood (above left), fleece from rayon staple fibers saturated with latex (above right), thermoplastically bound poly(propylene) filaments (below right), and spun-bonded poly(ethylene) (below left). The scale corresponds to 100 Acm. (After E. Trciber.)...

The treatment of wood fibres with isocyanate-bearing molecules and their incorporation into polyethylene were also recently studied [44]. In particular, the use of poly-(diphenylmethane diisocyanate) (XV) increased both the modulus of rupture (MOR) and the modulus of elasticity (MOE) of the ensuing composites. The use of stearic anhydride (XVI) as a novel compatibilizer further improved both MOR and MOE and enhanced the water resistance of the composites. 

Fig. 4. A computer-derived hydropathy plot for poly(ADP-ribose) polymerase. Seven-residue averages have been plotted by using a program based on the procedure of Hopp and Woods. All values above the horizontal line in the hydropathy plot indicated hydrophobic character, value below the line indicated hydrophilic character of the peptide. The three domains of the polymerase are illustrated along with the atypical amino acid compositions. (Taken from Ref. 3).

A wide range of adhesive types and chemistries are used to bond wood elements to one another (Table 2), but relatively few adhesive types are utilized to form the composites themselves. The vast majority of pressed-wood products use synthetic thermosetting adhesives. In North America the most important wood adhesives are the amino resins (qv), eg, urea-formaldehyde (UF) and melamine-formaldehyde (MF), which account for 60% by volume of adhesives used in wood composite products, followed by the phenolic resins (qv) eg, phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF), which account for 32% of wood composite adhesives (12,13). The remaining 9% consists of cross-linked vinyl (X-PVAc) compounds, thermoplastic poly(vinyl acetates) (PVA), soy-modified casein, and polymeric diphenylmethylene diisocyanate (pMDI). Some products may use various combinations of these adhesives to balance cost with performance. 

All-PPTA, tri-dimensional foamed consolidated FRP composite was prepared by embedding Kevlar 49 fibers in poly(A,A-di-sec-butyl-p-phenylene terephthalamide) resin [95]. The latter, on heating in the presence of benzenesulfonic acid catalyst, was dealkylated to form the PPTA matrix. In this way, Kevlar 49/PPTA molecular composites containing fiber fractions in the range of 8-40% by volume, having densities in the range of 0.2 to 1.2 g/cm, were prepared and their thermal and mechanical properties characterized. It has been pointed out that such all-PPTA composites mimic natural materials, e.g., the foamed composites prepared in this work had a remarkable resemblance to wood, with the advantages of flame and rot resistance. 

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