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Paper tensile properties as determined by fibre origin in the coniferous wood matrix Sun, Bernard Ching-Huey

Abstract

This study examines the hypothesis that coniferous wood fibre origin is maintained even when purified pulps are subjected to severe mechanical (beating) and chemical (decrystallizing) treatments. Four to five intra-incremental sulphate pulps obtained from each of three species, eastern larch (Larix lariaina (Duroi) K. Koch), Douglas fir (Pseudotsuga menziessii (Mirb.) Franco) and balsam fir (Abies balsamea (L.) Mill), were purified and machined to one or three levels EL (170 ± 45 ml Csf), DF (615 + 90 ml Csf; 328 + 43 ml Csf; 168 ± 62 ml Csf) and BF (190 + 30 ml Csf). Thereafter, cellulose supermolecular structures were altered by monoethylamine swelling, with changes (48 ± 2% vs. 68 ± 2%) quantified as fibre crystallinity index measured by X-ray diffractometry. Paper sheet apparent densities and tensile parameters (maximum strength, "stretch," modulus of elasticity and rupture energy) were determined. Fibre surface areas and sheet bonded states were estimated by light scattering coefficient measurements. The effects of wood origin on paper sheet physical-mechanical properties reported by other researchers were reaffirmed in this study, with all factors decreasing progressively across growth increments. The differences of wood intra-incremental, as well as species origins, were not removed by conventional pulping and papermaking processes, or additional treatments such as severe beating or major alteration of the basic cellulose structures as practiced in the study. Paper sheet tensile properties were related directly to sheet apparent density. Correlation coefficients as high as 0.979 and 0.989 were obtained for 00% and 82% monoethylamine decrystallized fibre sheets, respectively. Sheet density was inversely related to wood specific gravity and was found to be independent of wood species, degree of beating and decrystallization treatments. It is shown that fibre bonding potential is not the only factor influencing paper sheet strength. Intrafibre characteristics, such as cellulose supermolecular structures, have a highly significant effect on paper sheet strength as well. In addition, specific energy of "bond failure" (irreversible energy consumed per unit sheet surface formed as result of tensile straining) was higher for earlywood than for latewood sheets. This energy quantity depends on beating degree and differs according to species, as well as intra-incremental origin. The paper sheet light scattering coefficient (L.S.C.)-density relationship also depended on wood fibre origin. Earlywood sheet L.S.C. decreased with increased beating and sheet density, but latewood sheet L.S.C. remained almost unaffected. This observation explains why whole-wood fibre sheet L.S.C.-density relationships vary with pulp types as recorded in the literature.

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