Treatment of wheat straw with 1N trifluoroacetic acid (TFA) for 7 h at reflux temperature yielded 23% xylose based upon initial straw weight. This corresponds to about an 80% xylose yield based on the xylan content of the hemicellulose. The cellulose component of wheat straw was largely unaffected, as evidenced by low glucose yields. Decomposition of xylose by prolonged refluxing (23 h) was minimal in 1N TFA compared to 1N HCl. Treatment of wheat straw with refluxing 1N TFA converts about 10% of the lignin initially present in straw into water‐soluble lignin fragments. Fermentation of the xylose‐rich wheat straw hydrolyzate to ethanol with Pachysolen tannophilus was comparable to the fermentation of reagent grade xylose, indicating that furfural and toxic lignin by‐products were not produced by 1N TFA in sufficient amounts to impair cell growth and ethanol production. Cellulase treatment of the wheat straw residue after TFA hydrolysis resulted in a 70–75% conversion of the cellulose into glucose.
SynopsisWheat straw-g-polyacrylonitrile (PAN), containing 40% PAN, was saponified with sodium hydroxide and isolated under three sets of saponification and work-up conditions. Each reaction mixture was separated into a water-soluble and a water-insoluble fraction, which were individually analyzed for percentages (by weight) of synthetic polymer (saponified PAN), cellulose, hemicellulose, and lignin. Water solubles amounted to 14-24% of the total product and contained 70-74% synthetic polymer, the remainder being hemicellulose and lignin. Although water-insoluble fractions contained 52-54% saponified PAN, their water absorbencies were low (14-17 g HpO/g polymer). Treatment of these fractions with the enzyme cellulase converted 55-62% of the total cellulose to glucose.
A series of starch graft copolymers and one cellulose graft copolymer were prepared containing 40-50 percent synthetic polymer. The monomers used (styrene, methyl methacrylate, methyl acrylate, and butyl acrylate) were chosen to give grafted synthetic polymers with varying glass transition temperatures (Z,). These graft copolymers were extruded, in the absence of any added thermoplastic homopolymer, to give strong, continuous polysaccharide-filled plastics which are biodegradable and which exhibit little or no die swell. Properties of plastics varied with the T , of the thermoplastic portion. Starch-gpolystyrene and starch-g-poly(methy1 methacrylate) were hard and brittle, while graft copolymers prepared from methyl and butyl acrylate were more flexible and leathery. The graft copolymers with lower T , grafts required less torque and could be extruded at lower temperatures. In the methyl acrylate series, a graft copolymer prepared from gelatinized starch was more easily extruded than one prepared from granular starch, and addition of water produced a water-filled extrudate of excellent quality. The surprising feature of these results is that the matrix polymers, starch and cellulose, are rigid, nonsoftening materials. Grafting of a thermoplastic polymer to these matrix polymers would not be expected to give an extrudable product. The results are explained as powder flow followed by fusion or sintering of the graft polymers under the temperature and pressure conditions in the die.
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