| Bamboo crackless flattening technology is an efficient processing method that has emerged in recent years.Its appearance can effectively reduce the use of adhesives,improve the utilization of bamboo materials and added value of products.Soften bamboo by boil,microwave and high temperature saturated steam.The most suitable way of softening is obtained by measuring the moisture content and mechanical properties of the softened bamboo.Then vertically flatten bamboo with different characteristic after optimal softening to optimize the process.From the use of flattened bamboo performance,study the relationship between the softening process,the characteristics of bamboo and the appearance quality,physical and chemical properties,Tg of flattened bamboo panels to improve the mechanism of softening flattening of bamboo and further provide theoretical reference for the enterprise.Below are key research findings:(1)The moisture content of bamboo after boiled increases,and the MOE and MOR decreased.After boiled at 100℃ for 3 hours,the current MOE and MOR decreased by 41.7%and 4.4%.But the softening time is too long.The moisture content of bamboos after microwave softening decreases rapidly,and the MOE and MOR decreased firstly and then increase.After microwave softening in 360W for 1 minute,the current MOE and MOR decreased by 77.79%and 68.93%.The moisture content of bamboos after high temperature saturated steam decreased slightly,and the MOE and MOR decreased slightly.After softening at 200℃ for 6 minutes,the MOE and MOR decreased by 85.96%and 34.4%.After comprehensively comparing the changes in water content and mechanical strength of softened bamboo,the most suitable softening method is high temperature saturated steam treatment.At the same time,increasing the temperature of bamboo itself can effectively increase the plasticity.After the softening at 180℃ for 4 minutes,the MOE and MOR of the bamboo under the hot and humid condition(100℃ water boil for 3 minutes)decreased by 44.9%and 24.6%compared with the normal temperature.On the contrary,it also means that after the temperature of softened bamboo decreases,its mechanical strength recovers more,and the mechanical strength in practical use is better.(2)The effects of softening temperature and time,temperature of bamboo itself and outer layer on the characteristics of notch size and flattening are particularly significant.By increasing the softening temperature and prolonging the softening time,the width of the notch can be effectively increased,the flattening success rate can be improved,and the occurrence of surface cracks can be reduced.The width of the bamboo notches after softened at 180℃ for 8 minutes is 148.2mm,which is 166.5%higher than that at 140°C and 4 minutes.After the softening at 180℃ and 6 minutes,the bamboo flattening success rate is 100%,and there is no surface crack.As the temperature of bamboo itself decreases,the number of cracks after flattening increases and the success rate of flattening decreases.Removing outer layer can effectively increase the width of the notch and improve the flattening quality.The width of the notch with outer layer at 180℃ for 6 minutes is only 50.2%of that for bamboo without outer layer,and the flattening failed.The height,outside diameter and length of bamboo have little effects on the characteristics of notch size and flattening.The best softening process is obtained by the quality of the flattening bamboo plate.Bamboo should remove outer layer,the softening temperature is 180℃,the softening time is 6 minutes,and the softened bamboo should be flattened at the high temperature state as soon as possible.The bamboo flattening success rate can reach 100%and there is no apparent crack on the surface.(3)The infrared spectroscopy and X-ray diffraction pattern of bamboo after high temperature saturated steam treatment show that the number of hydroxyl groups and carbonyl groups of bamboo decreases,and the degree of crystallinity increases with the increasing of temperature and prolonging of time.This means that the dimensional stability of bamboo is increased accordingly,which facilitates later processing and utilization.When the bamboo is flattened vertically after 180℃,4 minutes softening treatment,its equilibrium moisture content decreased by 17.35%,air dry radial shrinkage decreased by 13.83%,chord shrinkage decreased by 6.95%,MOE decreased by 18.13%,and MOR decreased by 12.16%.SEM images show that phyllostachys pubescens of softened bamboo has been out of shape slightly.After being longitudinally flattened,the phyllostachys pubescens has undergone a large squeezing deformation,and subtle cracks can be observed inside.(4)The storage modulus and loss modulus of bamboo at 50℃ increased after softening treatment.With the increase of moisture content,the initial storage modulus shows a downward trend,and the loss modulus shows an upward trend.Tg is particularly affected by the water content and softening treatment.At 30%moisture content,the Tg of the original bamboo is 105.6℃,which is 47.07%lower than that of the dry state.The change of Tg is not obvious when the moisture content is above the fiber saturation point.With the increase of softening temperature and time,Tg is decreasing.After the softening at 180℃ for 6 minutes,Tg(30%MC)decreased to 88.8℃,15.19%lower than untreated.Increasing the water content and the softening temperature can effectively reduce the Tg of bamboo,increase the plasticity,and increase the flattening quality. |
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