Effect of PolyDADMAC on pretreatment of lignocellulosic and lignin-free biomass

Pretreatment is a necessary unit-process in bioconversion of lignocellulosic biomass. Major role of pretreatment is to remove or disrupt natural lignin shield and enhance the enzyme access to cellulose and hemicellulose in enzymatic hydrolysis. We have recently found that supplementation of small amounts of a water-soluble polymer, poly-diallyl-dimethyl-ammonium chloride (PolyDADMAC), during pretreatment can significantly increase the sugar yield in enzymatic hydrolysis of pretreated biomass. In order to verify the effects of PolyDADMAC on pretreatment, corn stover and switchgrass were pretreated with and without addition of PolyDADMAC under alkaline and dilute-acid conditions. Pretreatment experiments were carried out in batch reactor at 60-160 °C with liquid-to-solid ratio of 9. Treated samples were analyzed for composition paying special attention to delignification, and further examined by SEM to observe the structural change of biomass. Addition of PolyDADMAC in pretreatment has slightly negative effect on delignification, but altered the crystalline structure of cellulosic fibers quite significantly. The treated samples were subjected to enzymatic hydrolysis and the results were analyzed to assess the effects of PolyDADMAC. The effects of the polymer were found to be more significant on lignin-free biomass (Avicel, Solka Floc and Paper sludge). The positive effects of PolyDADMAC appear to be by direct interaction with cellulosic fiber, rather than with lignin or other extraneous components. A two-stage pretreatment method was then tested in which biomass was first treated with alkali or dilute-acid alone, then treated with PolyDADMAC. The results are analyzed in relation with the mechanism by which PolyDADMAC interacts with biomass.