Lignin-containing cellulose nanofibrils as reinforcement in polymer composites

Abstract

Cellulose nanofibrils (CNFs) are popularly utilized as reinforcement in polymer composites. The performance of a kind of hydrophobic CNFs in polymer matrix has attracted attention. The incompatibility between fiber and polymer might be improved by using hydrophobic CNFs without adding compatibilizer or surface chemical modifications. In this study, Lignin-containing cellulose nanofibrils (LCNFs) mechanically and chemically isolated from willow bark were utilized as the reinforcement. The homogenization of LCNFs was finished by 2, 6 and 12 passes through the Microfluidic M-110P after 60 min p-toluenesulfonic acid and 2 hours ‘Masuko’ grinding pretreatments. The hydrophobicity of LCNFs was speculated by the water contact angle of LCNFs film, which is approximately 104 ⁰± 3 ⁰. The LCNFs reinforced poly (lactic acid) composites were produced by two techniques: solvent casting and high-temperature extrusion-injection molding process. The content of LCNFs in composite was gradually increased from 0 wt% to 10 wt%.

We discovered that the LCNFs dispersed better in the composites produced by the high-temperature process. However, a poor interfacial interaction occurred in high-temperature process possibly due to the nanofiber damage and aggregation. The solvent exchange of LCNFs from water to chloroform succeeded by centrifugation and sonication system. The smaller size LCNFs (≤20nm width) after 12 passes through the Microfluidizer performed a better dispersion in the composite films produced by solvent casting method. 3 wt% LCNFs reinforced composites visually distributed more evenly but the incompatibility of the composites was proved by mechanical testing. The optical analyses were characterized by Scanning Electron Microscopy (SEM).