Study On Preparation And Performance Of Halogen-free Flame Retardant Polyolefin Transparent Films

Polyolefin film has the advantages of transparency,low temperature resistance,moisture resistance,water resistance and non-toxicity.It is widely used in the packaging field of furniture,gifts,toys,food and instruments.However,in recent years,fire accidents caused by the flammability of polyolefin packaging films have been increasing,which has greatly limited its application in the field of flame retardant packaging.Therefore,the improvement of flame retardant packaging materials has attracted more and more attention.While improving the flame retardant properties of polyolefin films,their transparency will be reduced.Therefore,flame retardant transparent polyolefin packaging films have become one of the research hotspots.How to improve the flame retardant properties of polyolefin films while maintaining the transparency of films has become the key to research.Based on this,this paper studies the process and grafting kinetics by preparing a new type of high-efficiency flame retardant and compatibilizer,and then studies its influence on the flame retardancy,transparency,mechanical properties and thermal stability of polyolefin film,which lays a solid theoretical and application foundation for the application of flame retardant polyolefin packaging films.In this paper,LLDPE-g-GMA was prepared by linear low density polyethylene(LLDPE)and glycidyl methacrylate(GMA),and the grafting process and grafting reaction kinetics were studied.The results show that:under the conditions of reaction temperature of 175℃,rotation speed of 60 r/min and reaction time of 10 min,the optimum ratio of each component is 3 phr of GMA;the mass fraction of dicumyl peroxide(DCP)was 0.15 phr;the molar ratio of styrene(St)to GMA was 0.75:1,and the grafting rate was up to 1.58%.The kinetic equation of the grafting reaction showed that the initial rate of the grafting monomer was proportional to the concentration of the grafting monomer and the concentration of the initiator by 1.01 and 0.74,respectively.The grafting activation energy was Ea=92.53 KJ/mol,and the kinetic equation was Re=Aexp(92.53/RT)[M]1.01[I]0.74Then,DOPO-KH560(DK-560)and DOPO-KH570(DK-570)were synthesized by silane coupling agent γ-glycidyloxypropyltrimethoxysilane(KH560)andγ-methacryloxypropyltrimethoxysilane(KH570)with flame retardant intermediate 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO),respectively.The synthesis process was studied and characterized by infrared spectroscopy.The results show that the synthesis process of DK-560 is that the reaction time is 5 h and the reaction temperature is 175℃.The synthesis process of DK-570 is that the reaction time is 8 h and the reaction temperature is 140℃.In the infrared spectrum,the P-H vibration absorption peaks of DK-560 and DK-570 at 2381.75cm-1 completely disappeared,while the characteristic absorption peaks of hydroxyl stretching vibration and carbonyl stretching vibration appeared at 3257 cm-1 and 1725.28 cm-1,respectively,indicating that DK-560 and DK-570 were successfully synthesized.The effects of different amounts of LLDPE-g-GMA on LLDPE/LDPE/HPCP/APP/SiO2 flame retardant system were further studied.The results showed that with the increase of LLDPE-g-GMA content,the oxygen index and mechanical properties of LLDPE/LDPE flame retardant system increased first and then tended to be gentle,and the light transmittance increased first and then decreased.Under the condition of LLDPE-g-GMA dosage of 4wt%.,the comprehensive performance of LLDPE/LDPE flame retardant system reaches the optimal level,the oxygen index is 24.8%,the tensile strength is 20.40 MPa,the elongation at break is 386.95%,and the film transmittance is 79.3%.Finally,the effects of three flame retardants DOPO,DK-560 and DK-570 on the flame retardancy,transparency,dispersibility,mechanical properties,thermal stability and char yield of LLDPE/LDPE flame retardant system and LLDPE/LDPE/LLDPE-g-GMA flame retardant system were studied.The results showed that with the increase of the amount of the three flame retardants,the oxygen index of the LLDPE/LDPE flame retardant system film increased with the increase of the amount of the flame retardant,and the transmittance of the film decreased slightly,among which DK-560 had the best comprehensive performance.Under the condition that DK-560 is 25wt%,the oxygen index of LLDPE/LDPE flame retardant system film is up to 28.6%,the carbon layer after combustion is the densest,the pores formed after flat combustion of the film are the smallest,the light transmittance is up to 78.2%,and the carbon residue rate is up to 20.27%.Scanning electron microscopy analysis shows that the dispersion of the system is the best,and the tensile strength of the system is 5.71 MPa and the elongation at break is 305.73%.Similarly,under the condition that DK-560 is 25wt%,the oxygen index of LLDPE/LDPE/LLDPE-g-GMA flame retardant system film is up to 29.8%,the film after combustion test has no holes,the highest light transmittance is 82.8%,and the highest carbon residue rate is 22.7%.Scanning electron microscopy analysis shows that the dispersion of the system is the best,and the tensile strength of the system is 11.64 MPa and the elongation at break is 345.73%.LLDPE/LDPE/LLDPE-g-GMA flame retardant system has better performance than LLDPE/LDPE flame retardant system.