Research On Softening Technology Of Furniture-Grade Small Diameter Round Bamboo

China has abundant bamboo resources and a diverse range of bamboo furniture,with round bamboo furniture being popular among consumers.Softening is the first and most crucial step in bending the curved parts of round bamboo furniture.The current softening process for small diameter round bamboo involves heating each piece over fire,which suffers from individual differences in softening effect,low repeatability,and low production efficiency.This study focuses on the commonly used bamboo(Phyllostachys iridescens)in small diameter round bamboo furniture to improve the softening effect and production efficiency.Firstly,the dynamic viscoelasticity of bamboo under different wall positions and moisture contents were studied to determine a reasonable softening temperature and range of bamboo moisture content.Then,two methods-high-temperature and microwave-were used to soften the bamboo,and the softening effect was measured by the elastic modulus(MOE)to compare the advantages and disadvantages of the two methods and select the superior one.For better softening process,orthogonal experiments were used for optimization to obtain the optimal process combination.The main research findings are summarized as follows:(1)From green layer to yellow layer,the storage modulus,loss modulus,and glass transition temperature(T_g)decrease.The T_g values of green,middle,and yellow layers are 123.3°C,118.9°C,and 103.7°C,respectively.As the moisture content increases,the storage modulus,loss modulus peak,and T_g decrease.At moisture contents of 0%,10%,30%,and 80%,the T_g values are 217.4°C,145.2°C,118.9°C,and 116.4°C,respectively.The difference in T_g between the 30%and 80%moisture content of bamboo is only 2.5°C,and the influence of moisture content on T_g is more significant below 30%.The softening temperature range of bamboo is approximately 103.7-217.4°C,with a moisture content greater than 30%during softening.(2)During high-temperature softening,temperature,time,and moisture content significantly affect the softening effect.As the temperature increases,the MOE first decreases and then increases,reaching a maximum decrease of 67.68%at 160°C;the modulus of rupture(MOR)generally decreases,reaching a maximum decrease of 56.13%at 160°C.As the time is extended,the MOE decreases,reaching a maximum decrease of 70.05%at 20 minutes;the MOR generally decreases,reaching a maximum decrease of 56.18%at 15 minutes.With the increase in moisture content,both the MOE and MOR decrease.The most significant decrease occurs at a moisture content of45%,with reductions of 86.65%and 68.34%,respectively.Within the scope of the experiment,increasing the treatment temperature and moisture content,and extending the softening time,are beneficial to softening.(3)During microwave softening,microwave power,time,and moisture content significantly affect the softening effect.As the microwave power increases,the MOE first decreases and then increases.At 500 W,it decreases the most,reaching 65.23%.The MOR first decreases and then increases;at 500 W,it decreases the most,reaching 41.97%.As the microwave time extends,the MOE decreases;at 360 s,it decreases the most,reaching 75.44%.The MOR generally decreases;at 360 s,it decreases the most,reaching 46.35%.Increasing the moisture content can reduce the MOE and MOR,with the most significant reductions at 45%moisture content,reaching 81.75%and 65.13%,respectively.Within the scope of the experiment,the higher the moisture content,the better the softening effect.Excessive power or time is not conducive to softening and can cause cracking.(4)Compared with microwave softening,high-temperature softening can reduce the elastic modulus more effectively and is less likely to cause bamboo cracking and scorching,making it a preferred softening method.Orthogonal optimization was applied to the high-temperature softening parameters,and the orthogonal experiment showed that at the 0.05 level,moisture content had a significant effect on the MOE and MOR.In contrast,the softening time significantly affected the MOE but not the MOR.The softening temperature had a generally significant effect on both the MOE and MOR.Within the experimental range,the optimal process combination was a temperature of 160°C,a time of 25 minutes,and a moisture content of 45%.