Preparation And Properties Of Bio-composite Film From Holocellulose

With the strategy of sustainable development,the comprehensive utilization of green renewable biomass has attracted more and attentions.At present,packaging materials are mainly come from petroleum-based plastics,which are difficult to degrade in the natural environment.In order to alleviate the shortage of natural resources and environmental pollution,it is urgent to develop biodegradable materials.Biomass is considered as a potential substitute for fossil resources.It can be degraded into harmless organic substances by soil in natural environment and has a wide application prospect in the field of degradable materials.Holocellulose was extracted from wheat straw by ultrasonic-assisted alkali method and was further modified by acetylation and carboxymethylation.The modified wheat straw holocellulose was further used to prepare biodegradable composite film.The main works are as follows:Wheat straw was pretreated by ultrasonic-assisted alkali method,and the effect of alkali concentration on the extraction process was investigated.When 0.6 wt%NaClO₂was used,giving 63.1%yield of holocellulose.The content of cellulose and hemicellulose in holocellulose were 59.1 wt%and 34.7 wt%,respectively.The structure and morphology of holocellulose were characterized by infrared spectroscopy（IR）,thermogravimetric analysis（TGA）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）.The results indicated that the crystallinity and thermal stability of wheat straw holocellulose extracted by ultrasonic-assisted alkali method were improved.Acetylated holocellulose（AHC）was prepared by the esterification reaction of wheat straw holocellulose with acetic anhydride.The effect of catalyst type and amount on the degree of substitution（DS）of AHC was investigated.When p-toluenesulfonic acid（TsOH）and sulfuric acid（H₂SO₄）were used as the co-catalyst,the DS value of AHC reached 2.16.AHC was characterized by IR,TGA,XRD and SEM,which confirmed the formation of AHC.The bio-composite film was prepared by co-blending AHC with reinforcing agents and plasticizers,and the effect of DS value of AHC on the performance of the bio-composite film was investigated.The bio-composite film was characterized by IR,TGA,XRD,nuclear magnetic hydrogen spectroscopy（¹H NMR）and SEM,and the results showed that the film-forming components had good compatibility.When CS and PVA,SOR and GLY were used as reinforcers and plasticizers,respectively,the AHC-based bio-composite film had good mechanical properties.The tensile strength,elongation at break,and Young’s modulus were 9.51 MPa,82.66%,and 54.43 MPa,respectively.The bio-composite film also had good disintegration and UV-blocking performance,and 59.2%degradation amount was acquired after biodisintegrating for 30 d and about 90%UV light was adsorbed.Carboxymethylated holocellulose（CMHCS）was prepared by the carboxymethylation reaction of wheat straw holocellulose with NaOH and monochloroacetic acid.The effect of catalyst type and amount on the degree of substitution（DS）of CMHCS was investigated.When polyethylene glycol（PEG）and cetyltrimethylammonium bromide（CTAB）were used as the co-catalyst,the DS value of CMHCS reached 2.46.CMHCS was characterized by IR,TGA,XRD and SEM,which confirmed the formation of CMHCS.The bio-composite film was prepared by co-blending CMHCS with reinforcing agents and plasticizers,and the effect of DS value of CMHCS on the performance of the bio-composite film was investigated.The bio-composite film was characterized by IR,TGA,XRD and SEM,and the results showed that the film-forming components had good compatibility.When CS and PVA,SOR and GLY were used as reinforcers and plasticizers,respectively,the CMHCS-based bio-composite film had good mechanical properties.The tensile strength,elongation at break,and Young’s modulus were 14.81 MPa,89.36%,and81.73 MPa,respectively.The bio-composite film also had good disintegration and UV-blocking performance,and 71.5%degradation amount was acquired after biodisintegrating for 45 d and about 90%UV light was adsorbed.Based on the results of performance and characterization of the bio-composite film,a possible degradation process for the bio-composite film was proposed.SOR and GLY were dissolved first.Subsequently,carboxymethyl in CMHCS,the N-acetyl and amino groups in CS fall off under the action of microorganisms,andβ-1,4-glycosidic bonds were broken.However,PVA was relatively difficult to degrade.