| Polypropylene(PP)is a thermoplastic synthetic resin with very good properties,which has the advantages of non-toxic,corrosion resistance,electrical insulation and excellent processing properties.It is widely used in the fields of construction,machinery,electronics,textiles,and packaging.However,PP is highly combustible,with a limiting oxygen index(LOI)of only 18,and generates a large amount of heat and smoke during the combustion process,which poses a great threat to the safety of life and property.The introduction of flame retardants is the simplest and most effective method to solve the flammability of PP.Ammonium polyphosphate(APP)and triazine charring agent(CFA)are the most commonly used intumescent flame retardants in PP.However,due to their large number of polar groups and weak interaction with nonpolar PP,poor compatibility and mechanical performance can be reduced,and flame retardants can migrate and precipitate in high-temperature and humid environments,resulting in flame retardancy failures.Therefore,it is necessary to improve the flame retardancy,smoke suppression,compatibility,and water resistance of PP to meet practical applications.The main research contents are as follows:(1)In the first part,the surface coating of APP/CFA system with hexadecyltrimethoxysilane(HTDMS)was used to obtain Si-IFR by in-situ polymerization.The effect of IFR with different coating amounts on PP was investigated.The results showed that when the amount of HTDMS was 14 wt.%of IFR,the comprehensive performance of Si-IFR was the best.The LOI of PP/27%Si-IFR samples increased from 35.5 to 36.4 before modification,and the THR decreased from 111 MJ/m~2 to 104 MJ/m~2 before modification.At the same time,the modified composite material still maintains the 1.6mm UL-94V-0 grade after being immersed in 70℃water for 7 days.Compared with the unmodified IFR,the change rate of oxygen index decreased from 8.5%to 0.8%,the change rate of tensile strength decreased from 6.2%to 2.9%,and the precipitation rate of flame retardant decreased from 1.59%to 0.59%,greatly improving the water resistance.The tensile and impact strengths of the composites also increased with the amount of HTDMS.(2)The second part introduces a modified 4A molecular sieve synergistic agent based on the above,reducing the total amount of flame retardant added,and improving the flame retardant efficiency and smoke suppression performance of the system..Firstly,zinc nitrate and 4A molecular sieve were used to introduce zinc ions through ion exchange to improve catalytic performance,and then boric acid was grafted onto the surface of molecular sieve to improve residual carbon strength.The results showed that when the total addition amount was 26 wt.%,the addition of 2 wt.%4A-Zn-B could make the composite reach the 1.6 mm UL-94 V-0 level,the oxygen index increased from 35.6 to 38.8,and the p HRR,THR,and TSP decreased by 27%,27%,and34%,respectively.The compactness of residual carbon was greatly improved.(3)In the third part,a modified ZnO synergist was introduced into the flame retardant system,and HTDMS was grafted onto the surface of ZnO to further improve the flame retardancy,smoke suppression,water resistance,and mechanical properties of the flame retardant system.The results showed that when the total addition amount was 26 wt.%,the addition of 2 wt.%Si-ZnO could make the composite reach the 1.6 mm UL-94 V-0 level,the oxygen index increased from 35.6 to 39.8,and the p HRR,THR,p HRR,and TSP decreased by 25%,19%,40%,and 37%,respectively.Compared to unmodified ZnO,the composite material after introducing Si-ZnO still maintains the UL 94 V-0 grade after soaking in 70℃water for 7 days,inhibiting the migration and precipitation of flame retardant,and maintaining a small flame retardant precipitation rate,LOI change rate,and tensile strength change rate.In addition,the introduction of Si-ZnO can significantly improve the tensile strength and impact strength of the composite. |
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