Graft copolymers of lignin as hydrophobic agents for plastic (wood‐filled) composites

Abstract

Poly[lignin-g-(1-phenylethylene)] graft copolymers synthesized by free-radical, graft copolymerization on lignin and verified by fractionation, infrared spectroscopy, and solubility change possess macromolecular surface activity as indicated by their capacity to form stable emulsions between incompatible fluid phases, to adhesively bond to wood surfaces, and to change the contact angle of water on coated wood. The surface activity of the copolymer changes with its composition. As the weight percent lignin in the copolymerization reaction product increases beyond 20 wt %, the amount of the emulsion phase formed in a water-benzene mixture decreases. Maple wood flour could be solvent-coated with a copolymer and both coated and uncoated maple flour could be extruded through a stranding plate into a wood-filled composite with polystyrene. Physical property tests show that composite control samples are about 3% stiffer and less deformable than are the copolymer composites when dry and about 5 or more percent more deformable than are the copolymer composites when wet, showing that the copolymer coating increased the wet strength. The copolymer samples are always denser than are the controls. Copolymer coating on wood filler decreases the swelling in the composite, the partial molar volume of the imbibed water, and the dimensional change in the solid. These effects cause increase in the density of the copolymer composite upon imbibition of water. Coating the wood component of the composite with a copolymer creates a hydrophobic barrier that produces a decrease in water imbibition into the composite, which will not disappear in 20 or more years of water immersion. Expansion in water is highly dependent on the direction of extrusion. The length expands about 1%, the width expands about five times as much, and the thickness expands over 10 times as much as does the length. This differential expansion may be due to the 22% reduction in the width and a 71% reduction in the thickness of the melt as it passes through the die and the alignment of the long axis of the fiber with the direction of flow through the die. The reaction product is a thermoplastic solid stable below 200°C and thermoformable at between 150 and 180°C. Products which contain between 10 and 50 wt % lignin are heterogeneous solids.

Progress in Green Polymer Composites from Lignin for Multifunctional Applications: A Review

“…However, for some applications, it is often difficult to blend lignin with other systems such as biopolymers. Some researchers have made efforts to modify lignin with different techniques in order to make it compatible with the polymer matrices. − Researchers from Stanford University have recently reported their study on the modification of lignin via a catalytic and solvent-free method . In this study, lignin was modified using a graft copolymerization reaction by graft polymerization of lactide onto lignin, and the reaction was catalyzed by triazabicyclodecene (TBD).…”

Properties and thermal degradation study of blend films with poly(4‐vinylpyridine) and lignin

“…6 Lignin, especially, with its many reactive hydroxyl groups, can form strong hydrogen bonding with many polymers, which has improved and modified the physical properties of the pure polymers. [7][8][9][10][11] Therefore, a blend film prepared from PVP with lignin could overcome the strong adhesion with the most solid surfaces as well as the brittleness of PVP.…”

“…Lignin is a nontoxic, commercially available, and low‐cost natural resource that has the potential to be utilized as a basic raw material in the chemical industry 6. Lignin, especially, with its many reactive hydroxyl groups, can form strong hydrogen bonding with many polymers, which has improved and modified the physical properties of the pure polymers 7–11. Therefore, a blend film prepared from PVP with lignin could overcome the strong adhesion with the most solid surfaces as well as the brittleness of PVP.…”

Fractionational and structural characterization of lignin and its modification as biosorbents for efficient removal of chromium from wastewater: a review

“…Therefore, physical, chemical, and enzymatic modifying methods are used to modify lignin structure to improve the efficiency of lignin application. In these methods, chemical modification is always adopted to enhance the lignin solubility, increase the blend compatibility, and improve the lignin mechanical properties [113][114][115][116][117][118][119][120][121]. It is well known that the lignin structure is rich with alcohol and phenol groups, therefore, the modification of lignin focus on esterification and etherification reactions [122,123].…”