1996
Cellulose (2019) 26:1995–2012
Graphical abstract
Keywords Individual softwood pulp fiber Single fiber elongation Stress–strain curve Tensile testing Viscose fiber
summerwood), compression wood (in softwoods), tension wood (in hardwoods), and variability in relation to radial and height position in a wood log (Groom et al. 2002; Lundqvist 2002; Gierlinger and Wimmer 2004; Luostarinen 2012). Additionally, pulp fibers are damaged, twisted or fibrillated in during chipping, pulping, and bleaching operations (Mott et al. 1995; Mohlin et al. 1996). In order to obtain reliable statistics for the pulp fiber properties, a sufficient number of fibers have to be tested. There are several studies on the tensile properties of pulp fibers (Leopold and McIntosh 1961; Jentzen 1964; Spiegelberg 1966; Hill 1967; Alexander et al. 1968; Hardacker and Brezinski 1973; Duncker and Nordman 1965; Page et al. 1972; Page and Seth 1980; Page and El-Hosseiny 1983; Groom et al. 2002; Jajcinovic et al. 2016). Typically, tensile strength and also elastic modulus are reported but strain at break is often disregarded. When stress–strain curves of indi- vidual restrained dried fibers are presented (Jayme 1959; Kallmes and Perez 1965a, b; Van den Akker et al. 1965; Duncker and Nordman 1965; Leopold 1966; Hardacker and Brezinski 1973; Groom et al. 2002; Mott et al. 2002), they are typically practically linear or slightly concave downward, with an elonga- tion to break of about 2–6%. Significantly higher elongation values ( * 20%) have been reported for Longleaf pine fibers cooked in laboratory conditions and dried under longitudinal compression (Dumbleton 1971), for commercial Southern pine kraft pulp fibers dried individually on a Teflon treated glass plate allowing drying shrinkage (Hardacker and Brezinski 1973), and for Loblolly pine fibers selected from the 5th annual ring at a low height of the tree (Groom et al. 2002; Mott et al. 2002).
Introduction
Properties of individual pulp fibers play a pivotal role in the development of the mechanical properties of fiber networks and structures. Fiber strength determi- nes the ultimate strength of paper and composite materials. However, the elongation potential of fiber networks is governed by the behavior of single fibers, inter-fiber bonding (Seth 2005) and the network properties (Vishtal and Retulainen 2014). Strength and extensibility of single fibers and the papermaking potential of fiber networks have been reviewed by Seth (2005), Lindstro¨m et al. (2005), and recently Vishtal and Retulainen (2014) and Hubbe (2014). High extensibility is a key material property for several paper packaging applications, e.g., paper sacks, paper cups or food trays. In this work, the effect of mechanical treatments on the load-elongation behav- ior of commercial bleached softwood kraft pulp (BSKP) fibers and the corresponding papers was studied in order to improve the extensibility of this type of materials. Due to the small length and width (0.7–3 mm length, 15–50 l m width) handling, mounting, and mechanical testing of individual pulp fibers is com- plicated and laborious. Another major difficulty regarding quantitative analysis is the natural variabil- ity of wood fibers caused by variation between trees. Furthermore there is variation related to location in the stem: early- and latewood (i.e., spring- and
123
Made with FlippingBook Digital Publishing Software