Determination of the interfacial properties between modified soy protein resin and kenaf fiber

Abstract

The kenaf fiber/soy protein resin interface was characterized. The soy protein isolate (SPI) was modified using a polycarboxylic acid, Phytagel® (PH), to make an interpenetrating network-like (IPN-like structure) structure of the resin. The effects of different PH contents on the interfacial properties were characterized using single fiber composite (SFC) tests and optical microscopy. Kenaf fiber strength was characterized using tensile tests. Kenaf fibers were extracted from nonwoven mats. The length of each kenaf fiber was extended by gluing it to long polyethylene filaments on both sides. After drying the glue, dog-bone shaped SFC specimens were prepared using pure and modified SPI resins. The dried SFC specimens were taken out from the mold and hot-pressed (cured) at 120°C. The interfacial shear strength (IFSS) was calculated using the shear-lag analysis. Single fiber tensile tests at different gauge lengths were performed. The average stresses were computed by fitting the data to Weibull distribution. These values were used in the calculation of the IFSS. After the SFC tests, the specimens were observed under the optical microscope to characterize the fiber fracture modes and the region around the fiber fracture. The SFC tests showed that the IFSS is a function of the PH content which controls the resin shrinkage. It was also seen that the interfacial failure mode is also a function of the PH content. These finding were confirmed by the microbead tests in which E-glass fibers were used with the modified SPI resins.