Synthesis Of Polycaprolactone-grafted Nanocellulose For Use In Shape Memory Polyrethane Composite

Nanocellulose is one of the most celebrated biomaterials in the materials community for a plethora of reasons that include their renewability,environmental benignity,vast abundance,biocompatibility,excellent physical strength and wide chemical-modification capacity.Thus,the preparation and application of nanocellulose are drawing a tremendous level of attention in both academia and industry in these decades.2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-mediated oxidation with post-mechanical treatment has been proposed as a promising and widely-used method for the preparation of nanocellulose.Since during the preparation of nanocellulose,significant amounts of C6 carboxylate groups were selectively formed on cellulose surface.In this paper,the effects of carboxylate groups on cellulose grafting PCL were investigated.Firstly,the influence of the form of the carboxylate group(H-type or Na-type)on the PCL grafting efficiency was explored.The two carboxylated celluloses(TOC-COONa and TOC-COOH)were grafted with PCL by ROP.The PCL-grafted cellulosic materials were characterized by Fourier transform infrared(FTIR),X-ray diffraction,elemental analysis,X-ray photoelectron spectroscopy(XPS)contact angle measurements and Carbon-13 nuclear magnetic resonance spectroscopy(13C-NMR)spectroscopic techniques and thermogravimetric(TG)analyses,respectively.The results indicated that TEMPO-oxidized cellulose with H-type carboxylate group(TOC-COOH)was more likely to be modified by polycaprolactone(PCL),and its corresponding PCL-grafted cellulosic materials was more hydrophobic than that of TEMPO-oxidized cellulose with Na-type carboxylate group(TOC-COONa).Before grafting,the two cellulose samples was very hydrophilicity(the contact angles of H-type and Na-type carboxylated cellulose were 22.6° and 31.4°,respectively),then after grafting,the the hydrophobicity were enhanced(the corresponding contact angles of grafted products were 79.4° and 54.9°,respectively).Secondly,a series of nanofibers with different carboxylate groups were prepared by changing the amount of NaClO,with the ultrasonic treatment.The morphologies and sizes,crystal structures,chemical structures and thermal stability of the nanofibers were studied by TEM,XRD,FT-IR and TG.The results showed that with the increase of NaClO amount,the content of carboxylate group increased.The higher content of carboxylate group,the better dispersibility of nanometer cellulose was in the water.And the TOCNs were rod-shaped nanometer cellulose crystals with average length of 160 nm.With the increase of NaClO content and the increase of carboxylate content,the crystallinity index increased slightly.Compared with natural cellulose,the thermal stability of carboxylated nanofibers was reduced.Finally,nano-celluloses with different carboxylate contents grafted PCL and the effects of different different carboxylate contents on the grafting efficiency were explored.Then,the PTOCNs and SMPU were mixed to prepare composite materials,whose mechanical properties and deformation were stabe.Then,the effects of PTOCNs,with different carboxylate contents and different grafting efficiency,on the properties of PTONC/ SMPU composites were studied.The results showed that the grafting efficiency of nanocellulose decreased with the increase of carboxylate content,and the percentage of PCL in the grafted products decreased,which affected the thermal stability and hydrophobicity of grafted products.The results showed that the thermal stability of the grafted product PTOCNs was lower than that of the TOCNs,the initial degradation temperature of PCL-grafted carboxylated nanocellulose decreased.And the smaller the carboxylate content of the nano-cellulose was,the more the initial degradation temperature decreased.When carboxylate groups of nanocellulose were 0.35mmol/g,0.47mmol/g,0.71mmol/g,0.83mmol/g and1.14mmol/g,the contact angles of the corresponding grafted products were 110.5°,99.1°,94.3°,91.6° and 74.2°,respectively.With the carboxylate content increasing,the hydrophobicity of the grafted products(PTOCNs)decreased.For the shape memory polyurethane and nanocellulose composites,the enhancement effect of PTOCNs on the strength of composites was better than that of TOCNs and it has less effect on the tensile stress and elongation at break.When the addition amount of PTOCNs in the composite membrane was 10%,the addition of nanometer cellulose significantly increased the elastic modulus of the composite membranes.With the increase of carboxylate contents,the increase of Young's modulus of PTOCNs was more obvious.On the other hand,with the carboxylate contents increasing,the elongation at break was reduced.The shape fixation rate and the shape recovery rate of the composites did not change greatly.Through the modification,the mechanical properties of the composites were improved while the elastic deformation properties of the composites were maintained.