Preparation And Flame Retardant Properties Of Poly(L-lactic Acid)-based Composites

As an environmentally friendly polymer,the poly?L-lactide??PLLA?has excellent biodegradability and is one of the most promising polymer materials.The PLA is completely degraded to H₂O and CO₂ under natural conditions and can be obtained from renewable plant resources.In addition,due to its excellent biocompatibility,good mechanical properties,high transparency and good processing properties,the PLLA is expected to replace some petroleum-based polymer materials.Through the research and development of the application of PLLA,it is beneficial to reduce the white pollution caused by waste polymer to the environment and saves oil resources.However,since it is still as flammable as ordinary synthetic thermoplastics,and the combustion process is always accompanied by lots of droplets,significantly limiting its application in the field of electronic products which needs to be flame-retarded.In this thesis,the properties,application,flame retardant mechanism of polymer composites,and research progress of flame retardant of PLLA were reviewed.In this thesis,the conventional phosphorus-based flame retardant ammonium polyphosphate?APP?was combined with inorganic particles hydroxyapatite?HAP?and the nitrogen-containing organic compound N,N'-ethylene?12-hydroxystearic acid amide??EBH,is used as a lubricant and dispersant?.The crystallization properties,thermal stability and flame retardancy of flame retardant PLLA composites were investigated by limiting the oxygen index?LOI?,UL-94vertical combustion,cone calorimeter and thermogravimetric infrared spectroscopy?TG-FTIR?.The flame retardant mechanism of the three additives was also analyzed.Through a series of pre-experiments to test the flame retardant effect of different components,it was finally determined that the flame retardant effect of the PLA-5 sample?10%APP,5%EBH,10%HAP and 75%PLLA?was best.?1?the APP,HAP and EBH enhance the crystallinity of the PLLA,increase the crystallization rate of the PLLA,shorten the crystallization time of the PLLA.?2?The LOI value rose from the original 19.0%to 28.5%,the V-1 level?UL-94 measurement?was achieved and the dripping behavior of the PLLA was suppressed at a certain extent;?3?the peak value of the heat release rate?PHRR?by the cone calorimeter test decreased by 61.6%compared with pure the PLLA,the total heat release value decreased by 32%,carbon residue amount reached 17.4%,total flue gas release decreased by 62%,effectively improving the flame retardant performance of composite materials;?4?From the digital picture of residual carbon and the scanning electron microscope image,it can be observed that a carbon layer with more dense,continuous and expandable can be found in the PLA-5,effectively reducing heat transfer and the volatilization of low molecular organic compound inhibits the entry of oxygen into the matrix,which improves the fire safety and attains the excellent flame retardance.?5?It can be seen by the test of the thermogravimetric infrared spectroscopy that the sample PLA-2?10%APP,10%EBH,80%PLLA?.The gas phase volatilization is higher than the pure PLLA and the P-N bond appears in the infrared spectrum.The volatilization of the low molecular compound cotaining the P-N bond can carry a lot of heat,but in the sample with the HAP,the IR peak of the gas decrease,the carbonyl and the aldehyde group peak intensity changes significantly It shows that the addition of HAP can effectively inhibit the decomposition of PLA matrix in the combustion process;?6?The flame retardant effect can be divided into three parts:?a?According to the thermogravimetric?TG?experimental results,at a lower temperature,the inorganic acid which reacts with the hydroxyl group to form carbon and can act as a dehydrating agent is released from the APP.At a slightly higher temperature,an esterification reaction takes place.The amount of coke remaining increases,mainly carbonation.?b?Based on digital pictures of carbon residue and scanning electron microscope images,carbon layers with expanded,dense and continuous morphology have barrier and protection.?c?Inert gases such as H₂O,CO₂,and nitrogen-containing gases produce a gas dilution effect.APP and HAP,EBH synergistic flame retardant,together in the gas phase and condensed phase,ultimately improve the flame retardant properties of the composite.