リサイクルによる木材パルプ繊維の変質 ＩＩＩ リサイクルによるパルプ繊維細胞壁の形態的変化

Abstract

After being beaten to about 350 ml C.s.f. by a Tappi Standard beater, commercial hardwood and softwood bleached pulps were dewatered by centrifuge in a cotton bag, shredded by hand and dried in a forced air circulation oven at 80°C for 6 days. Pulp fibres recycled 0, 1, 3 and 5 times by a sequence of wetting, defibrating, dewatering and drying, were wetted and dewatered by stepwise replacements with 30, 50, 70, 80, 90, 95 and finally 100% ethanol, succeeded by iso-amyl alcohol, which was flushed with liquid carbon dioxide in a critical point drying apparatus. Surfaces of these fibres were observed by a scanning electron microscope JSM-25. At the same time, fibre width was measured from SEM micrographs taken at the inclination angle of 0°. Also recycled fibres were fixed by Luft solution (1.2% KMnO4 & Veronal acetate buffer), followed by a stepwise dewatering by ethanol from 30 to 100%, a mixture of ethanol and propyleneoxide (1 : 1) and finally propyleneoxide. These fibres were embedded in a mixture of Epon 812, DDSA, MNA and hardner DMP 30. Embedded blocks were cut into a specimens thinner than 2, 000 Å by a ultra-microtome. Ultra thin specimens were electron stained with the Reynolds' lead staining method and observed under a transmittance electron microscope JEM-100 C. Handsheets of recycled fibres were dried on P2O5 and applied to a mercury intrusion porosimeter Shimazu 903-1 to measure the void volume.The following results have been obtained from the above experiments.(1) Parts of outer layer, Si, which were fibrillated by beating, were gradually removed from the surface of the fibre with recycling. This was supposedly taken place by separation of Si and S2 layers due to their difference in shrinkage rates during drying.(2) From the measurement of diameter of recycled fibres by SEM micrographs, a peak of the distribution curve for fibre diameter was shown to shift to the thinner side with recycling. (3) Separation of S1 layer from S2 layer and delamination of S2 layer were observed after 1st recycle from TEM micrographs as well. The more parts of S1 layer were removed from the fibre surface, the more S2 layer exposed. Fissures or cracks in the radial direction of the fibre wall appeared after 3rd recycle. After 5th recycle, S2layer was more exposed on the fibre surface, more delaminated and more split in the radial direction.(4) The mercury intrusion curves showed that the void volume of recycled fibre sheets increased with recycling at the pore diameter of severalμm, which correspond to the inter-fibre clearances and also of several tenths Am, correspond to pores in the cell wall. The latter seemed to be cracks appeared in the radial direction after 3 rd recycle on TEM micrographs. Finally, it can be concluded that fibre walls of recycled pulp fibres are irreversiblly changed by recycling so as to loose fibrillated S1 layer and to cause delamination and radial split in S2 layer.