Study On Strengthening And Toughening Modification Technology Of Bamboo Slivers For Winding/weaving Products

Bamboo,as a green renewable resource with abundant resources in China,has been obtained more and more attention.Bamboo has been made into bamboo slivers for weaving for a long time.Nowadays,the high toughness and axial tensile properties of bamboo slivers have been used in bamboo winding composite pipes with the iterative development of technology.However,when bamboo winding technology is applied to other products or wider fields,the toughness of bamboo slivers is not enough to bend into smaller shapes.Besides,bamboo has a gradient structure and the uneven distribution of the tissue structure causes significant differences within the bamboo material,resulting in different properties of the prepared bamboo slivers.In this study,the bamboo was divided into two layers,one was the bamboo slivers with many vascular bundles near the outer layer of the bamboo,and the other was the bamboo slivers with a few vascular bundles near the inner layer of bamboo.The fibers and parenchyma cells in the bamboo were mechanically separated.The effects of Na OH solution concentration,time,temperature and the drying method on the microstructure,chemical composition and mechanical properties of bamboo slivers were investigated.According to the changes in microstructure and chemical composition of fiber and parenchyma cells after alkali treatment,the effects of different cell structures on the performance of bamboo slivers and their mechanism were explored.The main results are as follows:(1)Alkali concentration had a significant influence on the microstructure,chemical composition,physical and mechanical properties of bamboo slivers.With the increase of Na OH concentration,the parenchyma cells in bamboo slivers collapse to form a compact structure,which led to size shrinkage and density increase.The content of hemicellulose and lignin were partially removed,and the crystal forms of fiber and parenchyma cell cellulose were changed after being treated at a high concentration.The tensile and bending properties of bamboo slivers were improved considerably.Compared with untreated bamboo slivers,the maximum tensile strength of treated bamboo slivers treated with 5%Na OH of outer and inner bamboo slivers increased by 55.70% and 99.40%,respectively.The modulus of elasticity of outer-and inner bamboo reached the maximum at 2% and 10%,respectively,with an increase of 109.09% and 69.57%,respectively.The bending performance of the inner bamboo slivers improved remarkably,especially when treated with an alkali solution with a concentration of 5%,bamboo slivers could bend into a cross shape,and the area change rate reached the maximum,which was 52.96% and 66.32% for outer and inner bamboo slivers respectively.(2)Drying method has an obvious influence on the microstructure and mechanical properties of bamboo slivers but had little influence on chemical composition and cellulose crystal form.After being dried in an oven,the internal structure of bamboo slivers was dense,the density increased,and the tensile and bending properties were improved.The tensile strength of outer and inner bamboo was increased by 55.70% and 99.40%,respectively,and the bending area change rate of inner bamboo slivers reached a maximum,which was 66.32%.After being dried by microwave,bubbles appeared in the bamboo slivers,and a large number of gaps between internal cells made the structure loose,which led to little improvement in tensile properties.However,the microwave drying process had a significant impact on the bending properties of outer bamboo slivers,in which the bending area change rate of treated bamboo slivers can be 62.68%.The cells in bamboo slivers freeze-dried kept in their original structure,sugars and proteins in the cavity of parenchyma cells were observed,which may lead to mildew.(3)The duration of alkali treatment had an obvious influence on the physical and mechanical properties of bamboo slivers.With the increased duration,the internal cells of bamboo slivers further collapsed which increased the density,but the chemical composition changed slowly,and the crystalline structure of cellulose did not change.The tensile strength of outer and inner bamboo slivers reached the maximum after 8 h and 6 h treatment,respectively,which was 62.08% and 103.23%higher than that of untreated one.The modulus of elasticity of treated outer and inner bamboo slivers reached the maximum when treated for 8 h,which increased by 77.31% and 61.71% compared with the untreated samples,respectively.The bending properties of outer and inner bamboo slivers were improved most when treated for 4 h and 6 h,respectively.The bending area change rate of treated outer and inner bamboo slivers was 66.75%and 77.90%,respectively.(4)Alkali treatment temperature had considerable influence on the microstructure,chemical composition,physical and mechanical properties of bamboo slivers.With the increase in alkali treatment temperature,the gaps between cells were further reduced,so that the interior of bamboo slivers was highly dense and the density increased significantly.The contents of hemicellulose and lignin decreased sharply,and the crystallinity increased considerably in inner bamboo and parenchyma cells.The tensile properties of outer and inner bamboo slivers were improved most when treated at 60℃ and 40℃,which increased by 86.57% and 132.02% compared with that of untreated samples,respectively.The modulus of elasticity of treated outer and inner bamboo slivers reached the maximum when treated at 80℃,which was 75.12% and 41.07%,respectively.The bending properties of bamboo slivers were improved when treated with alkali above 60℃ and could be completely wound on a nylon stick with a diameter of 10 mm without breaking.The bending area change rate of outer and inner bamboo reached the maximum when treated at 80℃ and 60℃,respectively,which were 81.46% and 84.74%.Compared with the concentration and time of alkali treatment and drying method,the temperature was much more important for improving the bending performance of bamboo slivers.High-temperature treatment can significantly improve the mechanical properties of bamboo slivers,especially the bending properties.To sum up,the optimal concentration,time of alkali treatment and dry method for both outer and inner bamboo slivers was 5%,hot air drying and 4 h.The best temperature of alkali treatment for outer and inner bamboo slivers was 80℃ and 60℃,respectively.The modified bamboo slivers with high strength and toughness can be twined and woven into more elements compared to the unmodified ones,which provides a new exploration idea for the future development of bamboo in more fields.