| The bamboo shoot shell is abandoned as agricultural and forestry waste,which causes the waste of resources and the environmental pollution.With the increasing emphasis on environmental issues and the decline in petroleum resource reserves,polylactic acid(PLA)composites have received more attention,especially for the preparation of plant fibers/PLA biodegradable composites is a research hotspot in recent years.If the bamboo shoot shell is made into fibers to modify PLA,which can achieve the recycling of bamboo shoot shell and protect the environment.At the same time,if the starch added into the bamboo shoot shell fibers/PLA composites,it can not only save the cost,but also improve the biodegradation of composites.In this paper,the bamboo shoot shell fibers as reinforcing phase were used to modify the starch/PLA matrix phase.The bamboo shoot shell fiber/starch/PLA composites with a low cost and excellent biodegradability were prepared by molding method.The best hot pressing parameters of composites were explored.The effects of different surface treatment methods on the properties of bamboo shoot shell fibers and composites were analyzed.And,the effects of bamboo shoot shell fibers content on the properties and soil degradability of composites were also studied.Finally the hydrolysis performance of composites in alkaline solution was analyzed.The results are as follows:(1)The hot pressing pressure,hot pressing temperature and hot pressing time on the effects of composites,physical and mechanical properties were analyzed by the orthogonal design.The best hot pressing parameters of composites were obtained by analyzing the variance of the physical and mechanical properties.The results show that the hot pressing temperature has the most significant effects on the mechanical properties of composites,followed by the hot pressing time and then the hot pressing pressure.Based on the analysis of mechanical strength,the best hot pressing parameters of composites are: hot pressing temperature of 185℃,hot pressing time of 6min,hot pressing pressure of 12 MPa.(2)The bamboo shoot shell fibers were modified by NaOH treatment,coupling agent treatment and NaOH+coupling agent treatment,respectively.The composites were prepared by the process parameters of hot pressing temperature 185℃,hot pressing time 6min,hot pressing pressure 12 MPa.The chemical groups and micromorphology of bamboo shoot shell fibers surface before and after modification were studied.And the properties of composites were studied by mechanical properties,SEM-EDS,contact angle and water absorption test.The results show that the 3 kinds of modification methods can improve the interface coMPatibility of composites in different degrees,and improve the properties of composites.Among which NaOH+coupling agent treatment has the best positive effects.FTIR and SEM show that the NaOH treatment can remove the surface gelatin,reduce the hydroxyl groups on the surface of bamboo shoot shell fibers and make them appear the grooves.Coupling agent treatment can chemically modify and smooth the surface of bamboo shoot shell fibers.After the bamboo shoot shell fibers were treated by NaOH+coupling agent treatment,the tensile strength and flexural strength of composites increase by 60.0% and 62.3%.The contact angle and 172 h water absorption rate of composites decrease by 12.7% and 34.0%,respectively.(3)The bamboo shoot shell fibers were modified by NaOH+coupling agent treatment,and the composites were prepared by the process parameters of hot pressing temperature 185℃,hot pressing time 6min,hot pressing pressure 12 MPa.The effects of bamboo shoot shell fibers content on the mechanical properties,surface morphology,thermal stability,surface wettability and water absorption of composites were studied by single factor experiment.The results show that the tensile strength and flexural strength of composites increase at first and then decrease with the increase of bamboo shoot shell fibers content,while the tensile modulus and flexural modulus show an increasing trend.When the bamboo shoot shell fibers content is 20%,the tensile strength and flexural strength of composites reach the maximum values of 33.1MPa and 50.3MPa.When the bamboo shoot shell fibers content is 40%,the tensile modulus and flexural modulus of composites reach the maximum values of 2212.5MPa and 4200.5MPa.With the increase of bamboo shoot shell fibers content,the thermal stability of composites become worse and the thermal decomposition residue increase.In addition,the surface wettability and water absorption of composites increase.(4)The bamboo shoot shell fibers were modified by NaOH+coupling agent treatment,and the composites were prepared by the process parameters of hot pressing temperature 185℃,hot pressing time 6min,hot pressing pressure 12 MPa.The effects of bamboo shoot shell fibers content on the soil degradation properties of composites were studied by single factor experiment.The results show that the addition of bamboo shoot shell fibers will improve the soil degradation of composites.The mass loss rate of composites in soil environment increase with the increase of bamboo shoot shell fibers content,and gradually increase with the increase of degradation time.After the composites were degraded for 30 days,the greater the bamboo shoot shell fibers content,the greater the loss of mechanical strength.After 90 days of soil degradation,the intensities of C—O and C=O stretching vibration peaks of PLA decrease with different degrees,but the position of the characteristic peak don,t change.The XRD results are consistent with the FTIR results,PLA characteristic diffraction peak intensity have different degrees of reduction,but the characteristics of diffraction the position of the peak do not change.After the composites are degraded for 90 days,their surface become rough,appeare some holes and larger grooves.(5)The bamboo shoot shell fibers were modified by NaOH+coupling agent treatment,and the composites were prepared by the process parameters of hot pressing temperature 185℃,hot pressing time 6min,hot pressing pressure 12 MPa.The composites were hydrolyzed by the alkali solution,the effects of different pH values on the hydrolysis performance of composites were studied by single factor experiment.The results show that the alkaline solution can cause the hydrolysis of composite.After being hydrolyzed for 96 h in alkaline solution of pH=10,pH=11 and pH=12,the mass loss rate of composites increase by 15.4%,17.4% and 21.2% respectively coMPared with 24 h after hydrolysis.Tensile strength and flexural strength decrease with the increase of hydrolysis time,and decrease with the pH value of alkaline solution.The results of FTIR and XRD show that the composites have no new characteristic absorption peak and diffraction peak after being hydrolyzed for 96 h in alkaline solution with different pH,but the intensity of characteristic absorption peak and diffraction peak has been reduced to some extent.The alkaline solution pH value will make the composite surface become rough,there are obvious holes and cracks,a large number of surface PLA flaked off.Bamboo shoot shell fibers and PLA will produce significant phase separation. |
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