Preparation And Properties Of Nanocellulose/Polyhydroxybutyrate Composite Films

Polyhydroxybutyrate(PHB)is a kind of thermoplastic resin with biodegradability,which has a broad application prospect.However,its brittleness,toughness and narrow processing window seriously limit its application.In order to improve the shortcomings of PHB,nanocellulose obtained by two different methods was introduced into PHB matrix as toughening agent,and water-soluble polyethylene glycol(PEG)was introduced to improve the interface compatibility between PHB and nanocellulose.The structure and properties of PHB/nanocellulose composite film membrane and PHB/PEG/nanocellulose ternary composite films membrane were characterized,and the toughening mechanism of the above two composite films membranes was revealed.The specific research content and results are as follows:(1)Through the single factor experiment,the effects of sulfuric acid mass concentration,acid hydrolysis time and acid hydrolysis temperature on the yield of cellulose nanocrystal(CNCs)were obtained,and the optimal acid hydrolysis conditions were obtained:64%sulfuric acid mass concentration,acid hydrolysis time 3h,acid hydrolysis temperature 25?.The yield of nanocellulose is 38.5%.The bagasse CNCs prepared by the method of hydrolyzing bagasse pulp by sulfuric acid exhibit a "narrow,two-tip" rod-like structure with an average diameter of 8.8 nm and an average length of 131.6 nm.The diameter ratio is about 15;The bagasse cellulose nanofibers(CNFs)were successfully prepared by mechanical grinding and high pressure homogenization to exhibit a grid-like structure,which were interlaced with each other and had an average diameter of 12.6 nm.After acid hydrolysis or mechanical shear force,the hydrophilicity of CNCs and CNFs was further enhanced,and the crystallinity of the fibers was improved,but the crystal type remained unchanged,both belong to cellulose type I.The thermal stability of bagasse cellulose is reduced after acid hydrolysis by acid and high mechanical shear.Both the amorphous regions of cellulose and the destruction of hydrogen bonds reduce the thermal stability of cellulose.(2)Two PHB-based biodegradable nanocomposite films were prepared by solution casting.The mechanical properties,cross section structure,surface morphology,crystallinity,thermal stability,light transmittance and barrier properties of the composite films were studied.The results showed that when the morphology of bagasse nanocellulose was rod-like and the content of bagasse nanocellulose was 1 wt%,the toughening modification of PHB was the best.The elongation at break of nanocellulose/PHB binary composite films increased from 3.40%to 6.5%,and Young's modulus increased from 1.4 GPa to 1.7 GPa.Compared with pure PHB,the elongation at break increased by 47.7%and 18.4%,respectively,but the tensile strength decreased slightly.This is because 1%nanocellulose reduces the crystallinity of PHB and the compatibility between them is good.Melting temperature,fastest decomposition temperature and crystallization temperature of PHB/CNCs and PHB/CNFs binary composite films membranes are higher than those of PHB pure membranes.It shows that nanocellulose can improve the crystal structure of PHB and the thermal stability of the composite films.The light transmittance of the composite film decreases as the nanocellulose content increases.When CNCs and CNFs were added to PHJB,the gas permeability of the composite films showed a trend of "decreasing-increasing",and the effect of adding CNCs was stronger than adding CNFs.The agglomeration effect of CNFs is stronger,resulting in the roughness of PHB/CNFs being greater than PHB/CNCs.(3)PEG with different molecular weight and content can improve the toughness of PHB/CNCs composite films.The toughening effect of 20%PEG 200 on PHB/CNCs is the best.At this time,the elongation at break of nanocomposite film reaches the maximum of 9.6%,which is 182.6%and 48.7%higher than that of pure PHB and PHB/CNCs,respectively.However,the tensile strength and Young's modulus of ternary composite films are lower than that of pure PHB and PHB/CNCs.With the increase of the addition amount of PEG(5wt%?20wt%),the melting temperature of PHB/PEG/CNCs composite film showed a continuous downward trend,and the smaller the molecular weight,the more the melting temperature of the composite film decreased.The water vapor transmission rate of the PHB/PEG/CNCs composite film first decreased and then increased.The oxygen transmission rate of the composite film membrane has been decreasing,which is related to the hydrophilicity of PEG and the compatibility of different components in the composite film.Compared with pure PHB and PHB/CNCs,the transmittance of the composite film increased.The addition of PEG improves the thermal stability and interfacial compatibility of the PHB/CNCs composite film.