| China is a large agricultural country.Pesticides,chemical fertilizers and other items used in the process of agricultural production are prone to the problems of floating and bag residue,which will cause harm to human body and the environment.The emergence of water-soluble packaging bags can solve the above problems.Starch（St）has a wide range of sources and low prices.Starch molecules contain many hydroxyl groups,making it hydrophilic and suitable for preparing water-soluble membrane.However,due to the high internal crystallinity of starch and the regular arrangement of molecular structure,the starch film is often brittle with poor flexibility and ductility,which cannot meet the practical application.Polyvinyl alcohol（PVAL）is a kind of polymer material that can be completely biodegraded.As PVAL molecular structure contains lots of hydroxyl groups,the film made of PVAL has the characteristics of good hydrophility,water solubility,high strength and high toughness as well as excellent gas barrier properties,oil resistance,heat-sealing properties,and high gloss and transparency.Although the PVAL membrane has excellent performance,the relatively high price hinders its application,the price of starch is low,the addition of starch is expected to reduce the cost,improve the rate of biodegradation and provide an effective way for the development and utilization of starch resources.Therefore,in this study,starch-polyvinyl alcohol degradable materials was prepared by flow extension method,the preparation process and application performance were explored systematically.The prepared film has good mechanical properties and excellent water solubility,and can be quickly dissolved in water,is expected to be applied in wet powder pesticides,water treatment agent packaging.This study can provide data and theoretical support for the promotion and application of water-soluble film.Firstly,the forming process of the degradable material were established by single factor and orthogonal tests.The study showed that the most influential factor on the tensile strength,the elongation at break and the water solubility of the water-soluble film was the proportion of starch,the amount of glycerol and the type of starch,respectively.In addition,glucose had a certain plasticizing effect.The optimum parameters for preparing the St-PVAL degradable material were as follows:the alcoholysis degree of PVAL was 88%,the addition amount of starch and polyvinyl alcohol was 60 g·L-1,the addition proportion of starch was 40%,the addition amount of glycerol was 5 g·L-1,and the addition amount of glucose was 10 g·L-1.Under these conditions,the tensile strength reached 26 MPa,the elongation at break reached 410%,and the water solubility reached 85%in 10 min.Then,the effects of the morphology of PVAL on the microstructure,crystallinity,thermal properties and hydrophilicity of degradable material were studied.Optical microscope observation showed that the particle size of PVAL decreased significantly after liquid nitrogen freeze crushing,increase the specific surface area,made it easy to interact with water.Compared with granular PVAL,the tensile strength,elongation at break of the films prepared by powdered PVAL were reduced by 23.06%,10.65%respectively,however,the water solubility was increased by 9.12%and the dissolution time was shortened by 180 s.Compared with granular PVAL,the PVAL film made with smaller particle size was more dense and uniform,and the roughness was smaller,the hydrophilicity was improved,the crystallinity was decreased.Besides,TGA analysis showed that powdered PVAL had good compatibility and thermal stability with water-soluble starch.At the same time,the effects of different starch addition ratio on the microstructure,crystallinity,thermal properties and hydrophilicity of degradable materials were studied.When the addition ratio of starch was high,it was easy to be unevenly distributed in PVAL matrix,and the agglomeration phenomenon was serious,the surface roughness of the film was increased,resulting in the reduction of mechanical properties and compatibility of St-PVAL degradable material.Moreover,the addition of water-soluble starch improved the hydrophilicity,reduced the crystallinity and thermal stability of the blend film.Overall,for powdered PVAL,the best addition ratio of starch was 30%.In this condition,the tensile strength was 27.88 MPa,the elongation at break was 375.51%,which met the requirements of"GB/T30768-2014 food packaging paper and plastic composite film bag"for mechanical properties.Finally,the application tests of the prepared degradable material were carried out.Through single factor and orthogonal tests,the optimal heat-sealing parameters were determined as follows:heat sealing voltage was36.0V,vacuum time was 3.0 s,heat sealing time was 2.5 s and cooling time was 1.0 s.In this condition,the heat-sealing strength of the degradable material reached 19.32 N/15mm.Compression and drop tests showed that the degradable bag prepared in this test could meet the requirements of"GB/T30768-2014 food packaging paper and plastic composite film bag"for stacking and transportation.Compared with pure PVAL membrane,the cost of the prepared St-PVAL degradable material was decreased by 23.94%when the water-soluble starch was added to 30%. |
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