Graft copolymers of lignin with 1-ethenylbenzene. 2. Properties

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The graft copolymerization of lignin and 1-ethenylbenzene was coinitiated by lignin, calcium chloride, and hydrogen peroxide in dimethyl sulfoxide solution. Conversion of 1-ethenylbenzene and yield of polymerized product of 90% or more were obtained. The copolymerization reaction changes the hydrodynamic radius of the product. Grafting has changed the surface properties of the original lignin from hydrophilic to hydrophobic. The copolymerization product is a thermoplastic material. White rot Basidiomycete were able to biodegrade styrene (1-ethenylbenzene) graft copolymers of lignin containing different proportions of lignin and poly(1-phenylethylene). The polymer samples were incubated with white rot Pleurotus ostreatus, Phanerochaete chrysosporium, and Trametes versicolor and brown rot Gleophyllum trabeum. White rot fungi degraded the plastic samples at a rate which increased with increasing lignin content in the copolymer sample. Both poly(1-phenylethylene) and lignin components of the copolymer were readily degraded. Poly(1-phenylethylene) pellets were not degradable in these tests. Observation by scanning electron microscopy of incubated copolymers showed a deterioration of the plastic surface. Brown rot fungus did not affect any of these plastics. The FTIR of the graft copolymers shows a series of characteristic absorbance peaks from multisubstituted aromatic rings and a strong poly(1-phenylethylene) (polystyrene) absorbance peak from monosubstituted aromatic rings. Subtraction of copolymer spectra taken after 50 days of incubation with the four tested fungi from spectra taken before incubation shows the loss of functional groups from the copolymer. The graft copolymer with long poly(1-phenylethylene) side chains is a macromolecular surface active material because in each graft molecule, a long hydrocarbon side chain has been grown off of a natural (oxyphenyl)propyl backbone. Surface activity of the graft copolymers is indicated by their capacity to form stable emulsions between incompatible fluid phases and to adhesively bond to wood surfaces. Dynamic contact angle measurement using the Wilhelmy plate technique shows that the graft copolymers change the contact angle of water on wood from 50 to 110°. The copolymerization product and its fractions have a coupling effect in the connection of wood to poly(1-phenylethylene). Lap shear strengths increase 56%, from 1826 to 2840 kPa, when the wood is coated with a graft copolymer containing 51.7% lignin.

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