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Kraft lignin as fiber treatment for natural fiber‐reinforced composites
Author(s) -
Thielemans Wim,
Wool Richard P.
Publication year - 2005
Publication title -
polymer composites
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.577
H-Index - 82
eISSN - 1548-0569
pISSN - 0272-8397
DOI - 10.1002/pc.20141
Subject(s) - lignin , materials science , composite material , fiber , ultimate tensile strength , natural fiber , contact angle , flexural strength , composite number , wetting , kraft paper , cellulose , chemistry , organic chemistry
Pine kraft lignin was sedimented from an aqueous NaOH solution (pH 13) onto flax fibers by submerging flax fiber mats in the alkaline solution for 5 min. This treatment has been used to improve the interfacial interactions between the hydrophilic flax and a hydrophobic soy‐oil‐based liquid molding resin. The flax fiber mat weight increase as a function of the lignin content in the alkaline treatment solution was determined and visualized using electron microscopy. Lignin sedimentation was found to decrease the contact angle between the resin and the treated flax fibers. Tensile and flexural properties of the composite samples showed an increase in mechanical properties with increasing lignin sedimentation, with a positive deviation for low lignin sedimentation. These results are in line with previous published data with hemp fiber composites [Thielemans et al. (2002), J. Appl. Polym. Sci. , 83, 323]. Improved properties are attributed to the improved wettability, while the low lignin content deviation is due to small lignin deposits protruding from the surface and thus improving mechanical interlocking. Features on the fracture surfaces, visualized by electron microscopy, are consistent with these findings. The soy‐oil‐based resin behaves similar to existing petroleum‐based unsaturated polyester and vinylester resins and its use is not inherent to the success of the lignin treatment. POLYM. COMPOS., 26:695–705, 2005. © 2005 Society of Plastics Engineers