Research On The Wheat Straw Making Biodegradable Composites And Its Characteristic

With the development of social technology and people's living standards,people give more emphasis on resource utilization when they realize their own development.As a typical agricultural country,the annual output of crop straw waste in China is about 720 million tons,ranking first in the world,which is a large renewable resource.However,the disposal means of most crop straw waste are burning or natural decay,instead of resource utilization.These two unreasonable disposal means both cause damage to the environment and influence people's life quality directly or indirectly.Consequently,research on the resource utilization of crop straw is an important subject.Wheat straw accounts for about 20%of the total quantity of crop straw and it is a representative one.This paper aims to find out a resource utilization method of wheat straw and discusses its potential risks.The experimental results are as follows:(1)Through the single-factor experiment,four factors that influenced the weight loss rate of Shumu are certained:shear length,the treatment temperature of NaOH,the mass fraction of NaOH and the treatment time of NaOH.Then multi-factor experiment of these four factors is performed.Through the regresstion equation deduced by the multi-factor experiemental results,the optimal technological condition of wheat straw fiber preparation is curtained:shear length is<0.2mm;the treatment temperature of NaOH is 69 ?;the mass fraction of NaOH is 6%and the treatment time of NaOH is 6h.Under optimal technological condition,the content of cellulose,hemicellulose,lignin and crude protein in wheat straw was determined.Compared with the content of wheat straw pretreated,the cellulose content of wheat straw treated was increased from 28.63%to 60.71%;the content of hemicellulose,lignin and crude protein decreased from 40.16%to 19.64%.Consequently,the cellulose content of wheat straw after treatment has largely improved and its mechanical strength is greatly enhanced correspondingly;hemicellulose,lignin and crude protein,which block the interfacial adhesion,are effectively removed.Hence the modified wheat straw would easily combine with matrix and owns better adhesion effects.(2)KH560(coupling agent)was used to modify the wheat fiber after alkali treatment.A scanning electron microscopical(SEM)were employed to examine the surface structures of original wheat straw and secondly modified wheat straw and the contact angle of the two kinds of wheat straw are determined.Results show that the difference of their structure is obvious.The surface structure of the original wheat straw was smooth and compact,with only a few protruding structures on its surface and its contact angle is relatively large,which against the permeation of matrix.The surface structure of the secondly modified wheat straw became disorder and loose,and showed different degree of concave and convex cracks;the smoothly waxy cuticle surface of the wheat straw disappeard through secondly modified.In addition,its surface roughness increased and its specific surface area increased correspondingly;and the contact angle decreased;the wetting performance was improved.The secondly modified wheat straw was more favorable for the matrix infiltration.And the adhesive effect is improved,favorable for compressing and forming with other matrixs.(3)Under different pressure,tempreture and time,the secondly modified wheat straw was compressed and formed with polylactic acid(PLA),propylene carbonate(PPC)and polyadipic acid(PBAT),respectively.Through the test of tensile strength,flexural strength and impact strength,the optimal process of compression was certained.The technology of compressing and forming on PLA and secondly modified wheat straw were optimized by the following conditions:mass fraction of wheat straw is 50%;hot pressing time is 6 min;hot pressing pressure is 10 MPa;hot pressing temperature is 170?.Under these conditions,the tensile strength of PLA was 6.534MPa;the flexural strength was 21.46MPa and the impact strength was 143.62J/m.The optimal preparation conditions of PPC and secondly modified wheat straw were as follows:mass fraction of wheat straw is 50%;hot pressing time is 6 min;hot pressing pressure is 10 MPa;hot pressing temperature is 160?.Under these conditions,the tensile strength of PPC was 7.61 MPa,the flexural strength was 18.56MPa and the impact strength was 153.59J/m.The optimum conditions of PBAT and secondly modified wheat straw were as follows:mass fraction of wheat straw is 50%;hot pressing time is 10 min;hot pressing pressure is 8 MPa;hot pressing temperature is 130?.Under these conditions,the tensile strength of PBAT was 4.38MPa,the flexural strength was 3.95MPa and the impact strength was 81.86J/m.(4)In the actual process of degradation,three kinds of degradable composite material degradation showed first increased and then decreased,the performance degradation from fast to slow the order:PLA biodegradable composites>PBAT biodegradable composites>PPC biodegradable composites;Three kinds of biodegradable composites crush for 3 min,then use it with distilled water configured the mass fraction of 1%,2%,3%,4%of the extracts,which use for the experiment on wheat seed germination.Results showed that the wheat seed germination rate,the longest root length,adventitious root number were inhibited,which reveals that the three kinds of degradable composite materials,which was crushed,could cause adverse effects on the germination of wheat seeds.This may be due to the degradable composite material after crushing produced more fine particles,together with the leaching solution into the cultivation of wheat in a petri dish in the process of cultivating hindered the germination of wheat seed,inhibits the growth of root system at the same time.Thus germination rate,root length and number of adventitious roots are affected.But the experimental results show that the lotus is notaffected by the experiment of leaching solution concentration.This is because the roots of wheat seeds that were added to the extract were more rough than those of the blank.Although the number is blank is less,the overall water absorption effect is still the same and its length is unaffected.