Strength and Crystalline Structure of Developing Acala Cotton

Abstract

Single fiber strengths and crystalline structures of greenhouse-grown Maxxa Acala cotton fibers at varying stages of development and at maturity are reported and compared with those of SJ-2 cotton fibers. Single fiber breaking forces of the Maxxa variety increase most significantly during the fourth week of fiber development; these increases correlate to the 60 to 90 mg seed fiber weight range. The forces required to break single fibers are similar for the SJ-2 and Maxxa varieties through the end of the fourth week of development. Beyond 30 dpa, both single fiber breaking forces and tenacities of the Maxxa cotton fibers are higher than those of the SJ-2 cotton fibers. Four waxd peaks located near 2θ angles of 14.7, 16.6, 22.7, and 34.4° are characteristic of the 101, 101, 002, and 040 reflections of cellulose I, respectively. The 002 peak intensity increases greatly during cellulose biosynthesis, indicating improved alignment of the glucosidic rings and improved order of atoms located within the glucosidic rings as the secondary cell wall thickens. The overall crystallinity and apparent crystallite sizes normal to the 101, 101, and 002 planes increase with fiber development for both varieties. Within each variety, the single fiber breaking forces are positively related to both the overall crystallinity and crystallite sizes. Between these two varieties, increasing breaking forces and tenacities appear to be related more to crystallite size than to crystallinity.