Effect of Chemical and Physical Cross-Linking on Tensile Characteristics of Solution-Blown Soy Protein Nanofiber Mats

Solution-blown soy protein/nylon 6 nanofibers, 40/60 and 50/50 wt/wt %, were collected on a rotating aluminum drum in order to form a mat The collected fiber mats were bonded both chemically (using aldehydes and ionic cross linkers) and physically (by means of wet and thermal treatment) to increase the tensile strength to increase the range of application of such green nonwovens. Chemical cross linkers bond different amino groups, primary amides, and sulfhydryl groups in protein structure. This is beneficial for the enhancement of tensile strength. Such mechanical properties of soy-protein-containing nanofiber mats as Young's modulus, yield stress, and maximum stress and strain at rupture were measured for different cross linkers at different contents. Overall, higher contents of cross linking agents in soy protein nanofiber mats resulted in nanofibers with higher strength which was accompanied by a less plastic behavior. Treatment with ionic cross-linkers resulted in nanofiber mats with higher Young's modulus of the mats. Covalent bonds formed by aldehyde groups had a smaller effect on the mat strength. As cross-linked nanofibers were exposed to heat, the bonds formed between amino groups in the fibers were broken and they became less aggregated. The overall increase of about 50% in tensile strength as a result of thermal bonding under compression was observed. In addition, wet conglutination of soy protein/nylon 6 nanofiber mats for 24 h under 6 kPa pressure led to partial physical cross linking of nanofibers and, consequently, to a 65% increase in Young's modulus. Solution blown soy protein/nylon 6 nanofiber mats were also subjected to aging in water for 1 h at 80 degrees C. An enhancement in the tensile strength of soy protein nanofiber mats was revealed after the exposure to water, as well as a slight plasticizing effect