| Polylactic acid(PLA)is a kind of thermoplastic resin.Its raw materials are mainly potato,corn,etc.It has excellent characteristics of biocompatibility and complete degradation,and its degradation products are H2 O and CO2.However,PLA also has congenital insufficiency.Its shortcomings,such as flammability in the air,dripping and poor toughness,have largely restricted the wide application of its products.Therefore,it is necessary to perform flame retardant and toughening modification of PLA.Based on the review of the PLA halogen-free flame retardant research status,this paper proposes the preparation of environmentally friendly PLA composites by melt ultrafine barium sulfate(BaSO4)and bamboo fiber(BF)which set as modifiers.What's more,Microstructure,mechanical properties,thermal stability and combustion characteristics have been systematically studied.The main research contents are as follows:1.ultrafine BaSO4 was used as a modifier,The PLA/BaSO4 composite was prepared by melt blending.The thermal stability,combustion behavior and influence law of mechanical properties of PLA/BaSO4 composites were investigated by means of limiting oxygen index(LOI),thermogravimetric analysis(TGA),vertical combustion(UL-94)and universal testing machine.The combustion results show that the LOI of pure PLA is only about 21%;when the addition amount of BaSO4 is 5.0%~20.0%,the LOI value of the composite increases to 21.5%~22.6%,and the UL-94 flame retardant grade reaches V-2.Grade,but when the amount of BaSO4 added further increased to 25.0%,the LOI value decreased to 21.8%.TGA analysis found that the char residue rate of the composite increased significantly with the increase of BaSO4 content.The mechanical tests show that with the increase of BaSO4 content,the impact toughness of PLA composites increases first and then decreases.When the addition amount reached 10.0%,the impact toughness reaches the maximum value of 21.98 kJ/m2,which is higher than that of pure PLA.52.7%;however,excessive BaSO4 will reduce the impact toughness of PLA/BaSO4 composites.2.BF was flame retardant modified by phenylphosphoric acid(denoted as PHPABF)with and preparation of PHPA-BF/PLA composite.The results show that the addition of PHPA-BF can improve the flame retardancy of PHPA-BF/PLA composites to some extent.As the amount of addition increases,the LOI value also increases.When the addition amount increases from 7.5% to 50.0%,the LOI value increases from 24.5% to 27.0%,although the UL-94 flame retardant grade of the sample does not change significantly.All are V-2.This is mainly due to the introduction of BF to promote the formation of a relatively dense carbon residue layer,which has the effect of insulating the air from flame retardant and protecting the material.The TGA results show that PHPA-BF can significantly improve the high temperature thermal stability of PLA and increase the char residue rate,but it reduces its mechanical properties,which is closely related to the obvious interface separation between the two.3.BF was modified with phytic acid(denoted as PA-BF),and PA-BF/PLA composite was prepared.The results show that the LOI value of PA-BF/PLA composites increased significantly from 24.1% to 30.5% when the addition amount of PA-BF increased from 7.5% to 50.0%.The UL-94 flame retardant rating has been increased from V-2 to V-0,and there is no obvious melting phenomenon.Compared with PHPABF,PA-BF can significantly improve the flame retardant properties of PLA composites,forming a complete and dense char layer,showing superior thermal insulation,oxygen barrier and protective matrix properties.The TGA results show that the high temperature thermal stability of PA-BF/PLA composites is significantly improved,and the char residual rate is greatly increased.Mechanical tests show that PA-BF has a certain toughening effect on PLA compared with unmodified BF and PHPA-BF.SEM showe that when the amount added is small,PA-BF was more uniform in PLA matrix and had better interfacial compatibility.Compared with PHPA-BF,although the presence of PABF also led to the decline of mechanical properties,but the decrease was Significantly lower than the former.Figure[34] Table[14] reference[82]... |
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