Research On Lightweight And Flame Retardancy Of Automotive Polypropylene

AS one of the three major plastic,foamed polypropylene(PP)with microcellular pores has unique advantages such as light weight,rigidity and toughness,and high temperature resistance compared to the oridinary PP,making it widely used in various aspects.However,ordinary PP foams showed large pores,and complex foaming processes and expensive equipment are always needed for their preparation.In this work,sodium bicarbonate(NaHCO₃)was used as the foaming agent,and the anti-solvent recrystallization method was used to reduce its size to improve the foaming efficiency and reduce the size of PP pores accordingly.Furthremore,piperazine modified ammonium polyphosphate(PA-APP),as the flame retardant,was added into PP matrix through a simple process and low cost method,resulting in modified PP composited with improved flame-retardancy.Also,the effect of PA-APP on the flame-retardant properties of PP foam was investigated.The main research are as follows:(1)NaHCO₃ particles with smaller size were prepared by anti-solvent recrystallization method.Using absolute ethanol as the anti-solvent,the NaHCO₃aqueous solution was recrystallized,reducing the size of the NaHCO₃ particles significantly.Results showed that the smallest NaHCO₃ particles(383 nm)was obtained as the mass fraction of NaHCO₃ in the NaHCO₃ solution was 10 wt.%,the mass ratio of the main solvent and the anti-solvent was 1:15,the stirring speed was1500 r/min,the reaction temperature was-10°C,the feeding rate was 1 m L/min,the addition amount of the surfactant SDS was 12.5%of the mass of NaHCO₃,and inlet diameter is 1.5 mm.(2)Decreasing the size of NaHCO₃ particles would lower its decomposition temperature,making it not match with the processing temperature of PP foaming.Thus,stearic acid was applied to modify NaHCO₃ particles with improved thermal performance.Results showed that the decomposition temperature of stearic acid modified NaHCO₃ particles was increased to 160?from 99.5?of unmodified NaHCO₃ particles.Foming experiments showed that the pore size of the foamed PP reached 500 nm while using the modified NaHCO₃ particles as foaming agent.And the best performance of foamed PP can be achieved as 6 wt%modified NaHCO₃ particles was added.However,the combustion test of the foamed PP sample showed that the limiting oxygen index(LOI)and the UL94 test of the foamed PP did not change significantly compared with pure PP,indicating the poor flame-retardant performance.(3)In order to improve the flame-retardant performance of PP,PA-APP was introduced into PP matrix during the foaming process as the flame retardant.Results showed that the LOI of pure PP was only 20.9%,while adding 15 wt%PA-PP,the LOI was increased to 29%,reaching the flam-retardant level.And the UL94 test also reached V-1 level.Further increasing the content of PA-APP to 20 wt%,the UL94 test of the PP foam could reach the highest level of V-0.In addition,compared to pure PP foam,the the peak heat release per unit area(PHRR)of the PP foam containing 20 wt.%PA-APP was resuced by 69%,while the total heat release per unit area(THR)was dropped by59%,the amount of CO₂ produced dropped by 65%,and the lighting time was delayed from 15 s to 35 s.The results proved that the introduction of PA-APP effectively improved the flame-retardant performance of PP foam.