Research On The Relationship Between Growth Stress And Bamboo Properties Of Phyllostachys Pubescens

In recent years,under the background of global plastic restriction,bamboo,as a biomass material with advantages such as green,low-carbon and degradable properties,has provided a sustainable development solution-"replacing plastic with bamboo"-to solve plastic pollution problems,promote energy conservation and emission reduction,and respond to climate change,providing opportunities for the high-speed and high-quality development of the bamboo industry.Like trees,bamboo is also susceptible to stimulation from tree themselves or external environment during the growth process,which in turn produces growth stress affecting material properties and ultimately restricting the processing and utilization of bamboo.Growth stress also exists in many plants,and more and more scholars are focus on this,but there are few reports in the field of bamboo.In this study,taken Phyllostachys pubescens from Anhui,the growth stress variation and the microscopic,chemical and physical mechanical and growth strain relationships of bent bamboo at different heights were investigated for further research in the fields of biological structure and function,material processing and utilization of bamboo.The main research results are as follows:(1)The growth strains in both upright and bent bamboo were asymmetrically distributed,and the growth strains in the upper tensile stress region(TB)and the lower corresponding region(OB)of bent bamboo were very different,with negative values(tensile stress)in the TB region and positive(compressive stress)and negative(tensile stress)values in the OB region.There was no obvious pattern in the growth strain values of bent bamboo at different heights;however,at the same height,the growth strain absolute values in the TB region of bent bamboo were much larger than those in the OB region,and the height range with large differences in growth strain values were all in the range of 3-5.4 m,which was approximately in the area with the largest curvature of each selected bamboo plant.(2)There was eccentricity in the cross-section of bent bamboo,and the wall thickness in the TB region of bent bamboo at the same height was generally lower than that in the OB region.The average value of fiber lengths in the TB and OB regions of bent bamboo were 1495.05μm and 1785.24μm,which were larger than the 1430μm measured by previous authors;the average value of fiber diameters in the TB and OB regions of bent bamboo were 7.37μm and 9.31μm,the average value of fiber length-width ratio in the TB and OB regions were 222.57 and 205.57.The fiber length and fiber diameter in the TB region were lower than those in the OB region,while the fiber length-width ratio in the TB region was greater than that in the OB region.The double-wall thickness of fiber cells in the TB region was smaller than that in the OB region,while the fiber tissue ratio was higher than that in the OB region.The fiber length,fiber diameter,fiber length-width ratio and fiber cell double-wall thickness were significantly correlated with growth strain in the TB region of bent bamboo,but not in the OB region of bent bamboo,except for the correlation between fiber length-width ratio and growth strain.(3)There was no significant difference in the chemical composition content between the TB and OB regions of the bent bamboo.The laser confocal microscopy effect showed that the vascular bundles in the TB and OB regions of bent bamboo were spontaneous fluorescence to different degrees,but the difference in fluorescence intensity was not significant.Fourier infrared spectroscopy(FTIR)and the characteristic peaks were found by infrared imaging analysis,revealed no significant difference in the cellulose,hemicellulose and lignin contents and distribution in both the TB and OB regions of bent bamboo.The average values of micro fibril angle and crystallinity were 8.12°and 9.18° in the TB and OB regions,and the average values of crystallinity were 38.94%and 40.44%in the TB and OB regions,as measured by X-ray diffractometry(XRD).The microfibril angle and crystallinity in the TB region were smaller than those in the OB region,but the differences were not significant,and there was no significant correlation between microfibril angle and crystallinity and growth strain in the TB and OB regions of bent bamboo.(4)The basic density of bent bamboo ranged from 0.627-0.765g/cm3,and there was no significant difference between the TB and OB regions.The dry shrinkage,bending strength and bending modulus of elasticity,and tensile strength parallel to grain of bent bamboo were generally higher in the TB region than in the OB region,except that the compressive strength parallel to grain was lower than in the OB region.Among the air-dry shrinkage indices of bent bamboo,only the radial and chordal air-dry shrinkage in TB region showed significant correlation with growth strain,other indicators did not show significant correlation;among the oven-dried shrinkage indices of bent bamboo,only the volumetric oven-dried shrinkage in OB region did not show significant correlation with growth strain,other indicators showed significant correlation.The basic density,bending strength and bending modulus of elasticity,and tensile strength parallel to grain of bent bamboo were not significantly correlated with growth strain.