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 °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.