(490b) Lignin Filers in Polylactic Acid Composite: The Effects of Impurities in Lignin and Lignin Type

Authors: 
Bai, X., Iowa State University
Gao, Y., Iowa State University
Qu, W., Iowa State University
Lignin filers in polylactic acid composite: The effects of impurities in lignin and lignin type

 Yiwei Gao, Wangda Qu, Xianglan Bai

Lignin is second largest biopolymer on Earth. Lignin byproduct is abundantly available from paper and pulping industries, as well as emerging biorefineries. Due to its low cost, aromatic polymer structure and carbon rich nature, utilization of lignin for value-added products has been of great interest. For example, lignin filer is blended with other polymers to improve the properties of the composite materials, lower the product cost and enhance biodegradability. It is known that isolated lignin often contains considerable amount of inorganic impurities, and the impurities could affect the properties of lignin. Although the impurities are removable, purifying lignin can be a costly process. In the present study, the effect of impurities on the performance of lignin as the filer was studied by blending polylactic acid (PLA) with corn stover organosolv lignins with different amounts of impurities. The impurity content in the lignin was controlled by acid washing raw lignin with different numbers of washing and rinsing cycle. The PLA-lignin composites were characterized for their thermal, chemical and mechanical properties. Overall, blending corn stover lignin with PLA reduced the tensile strength of the composite but increased its modulus compared to pure PLA. When the ratio of lignin to PLA was fixed, using higher ash containing lignin resulted in the composite with better tensile strength. However, the composite with highest modulus was obtained with the lignin filer containing an intermediate amount of ash. For the lignin filer with fixed ash content, the composite containing 10% lignin filer had both highest tensile strength and modulus. It was also found that using raw lignin containing 7% of ash reduced thermal stability of the composite due to catalytic effect of the impurities for thermal decomposition. However, the lignins with lower ash contents did not significantly affect the thermal stability of the composites. A biorefinery produced hardwood lignin was also used as the filer in PLA to investigate the effect of lignin structure on the performance of lignin filer.