ABSTRACT
The utilisation of cotton plant stalks for papermaking, as an alternative to the wasteful disposal of the crop residue by burning, was explored in this study, using four varieties of American upland cotton plants (Gossypium hirsutum), namely: SAMCOTs 6, 8, 9 and 10 grown in Nigeria. Wood and bast fibre characteristics, such as fibre wall thickness, fibre diameter, fibre length, runkel ratio, thickness index, flexibility coefficient and slenderness ratio were determined. The composition of alpha-cellulose, hemi-cellulose, lignin, ash and moisture were also determined. The fibre length, runkel ratio and slenderness ratio were found to be 0.270mm, 0.540 and 12.7, respectively, on the average, for both wood and bast fibres. Varietal effects on most of the fibre characteristics were found to be significant at 95% probability level. SAMCOT 9 was found to be the best variety in most fibre characteristics, followed by SAMCOTs 10, 8 and 6. The alpha-cellulose content of the stalks averaged 54.0%, which was high enough to be explored for papermaking. In view of the low runkel ratio and short fibre length of the stalks, thermo-mechanical pulp (TMP) was prepared from each variety and blended with at least 40% of waste paper (WP) whose fibre length averaged 2.00 mm, and it improved the sheet formation and the strength properties of the hand sheets. Factorial three-factor papermaking experiments involving two levels each (2x2x2) of furnish ratio (TMP/WP), pulp freeness and additive were conducted. Standard hand sheets were produced and tested for physical and mechanical properties. For the furnish ratio (TMP/WP) of 60/40, freeness of 35°SR and additive of 1% rosin and 4% alum, the caliper, basis weight, burst strength and tear strength of the hand sheets averaged 0.510 mm, 127.8 g/m2, 0.420 kPa and 0.820 kN, respectively. SAMCOT 8 hand sheets consistently maintained the highest tear strengths, followed by SAMCOTs 10, 9 and 6. The basis weight versus caliper relationships for SAMCOTs 6,8,9 and 10 hand sheets were found to be linear, with high and positive correlations and the coefficients of determination r2 were 0.958, 0.997, 0.914 and 0.866, respectively. The paper strength properties correlated positively with the original fibre characteristics of SAMCOTs 6, 8, 9 and 10 cotton plants and were found to have linear relationships. The tear strength versus runkel ratio, fibre length and slenderness ratio relationships had coefficients of determination r2 of 0.674, 0.927 and 0.812, respectively.
