The use of kapok fiber to improve strength of paper

Abstract

This research aimed to find the optimal pulping condition of kapok fiber to be used in papermaking. The variables used were pulping condition in terms of sodium hydroxide dosages and refining condition in terms of disc gap distances and numbers of refining pass. The influence of kapok pulp on paper properties was also investigated when kapok pulp was mixed with commercial hardwood and softwood pulps. The experiment was started by immersing kapok fiber in water for 3weeks. Then, kapok fibers were pulped using a soda process with different sodium hydroxide dosages (10, 15, 20, and 25% based on the oven-dried pulp weight) at 120 ºC for 2 h. The kapok pulp was then refined twice by a disc refiner with a 10/1000 inch disc gap. The handsheets having a basis weight of 60 g/ m² were made, and paper properties were examined to determined the optimum condition providing the best strength properties. The optimum pulping condition was then used in the next step in which the pulp was refined by 3 refining conditions which were 1) 7/1000 inch disc gap for one pass; 2) 10/1000 inch disc gap for one pass followed by 7/1000 inch disc gap for one pass; and 3) 10/1000 inch disc gap for two passes. The optimum refining condition was then used in the next step in which the pulp was bleached using hydrogen peroxide (3% based on the oven-dried pulp weight) at 80 ºC for 2 h. The bleached kapok pulp was then mixed with commercial hardwood and softwood pulps at different ratios. The results indicated that higher sodium hydroxide dosage decreased the pulp freeness and tear resistance but increased apparent density, smoothness, tensile strength and burst strength. The optimum dosage of sodium hydroxide was 20% based on the oven-strength and burst strength. The optimum dosage of sodium hydroxide was 20% based on the oven-dried pulp weight since the highest tensile strength was obtained. The optimum refining condition was the two-pass refining at the 10/1000 inch disc gap because the kapok pulp provided highest strength properties. The kapok pulp in mixed pulps improved tensile strength of the sheet but decreased tear resistance. Furthermore, the result shows that the kapok sheet had the higher water contact angle than the sheets from the commercial pulp. Thus, the kapok pulp mixed with the commercial pulp could improve water repellency of the sheet.