| Polypropylene(PP)is widely used as a water-barrier layer in food packaging films due to its excellent properties such as non-toxic,odorless,and water-barrier properties.However,due to the high oxygen permeability of single-layer PP film,it should be composited with good oxygen-barrier material like polyamide(PA)and ethylene-vinyl alcohol copolymer to prepare multilayer composite film.Since PP is a kind of non-polar polymer with low surface energy,it is difficult to be composited with polar polymers.An adhesive layer should be introduced to assist the preparation of composite films.At present,maleic anhydride(MAH)grafted PP(PP-g-MAH)is the most commonly used material for adhesive layer in PP-based food packaging composite films.which is mainly prepared by melt grafting method.In this process,PP is severely degraded and unreacted monomer in PP is difficult to remove,which will adversely affect the adhesive properties of composite film and the security of food.Therefore,how to improve the adhesive properties of PP without affecting the bulk properties and effectively remove residual monomer is a key issue in the preparation of PP-based composite film.In this paper,MAH was grafted onto the surface of PP film by microwave-induced surface grafting technology,the adhesive properties between PP film and PA6 film was significantly improved,while the problems of residual monomer and degradation of PP could be effectively solved.The thesis carried out systematic researches on the surface analytical methods of the modified PP film grafted with MAH,processes and mechanisms of microwave grafting reaction under different solution systems,composite adhesive characteristics between modified PP film and PA6 film.etc.The following research results were obtained:1.Analytical methods were established for residual monomer,surface properties and adhesive properties of the microwave-induced grafting modification of PP film.Extraction under high pressure-ultraviolet spectroscopy method was established for quantitatively detecting the content of residues in the modified PP,and it was found that the content of residues in microwave-induced grafting modified PP film was much lower than that of commercialized PP-g-MAH,and the residues could be removed quickly by soaking in acetone.Additionally,the grafting of MAH on the surface of PP film could be analyzed qualitatively and quantitatively through the changes in surface hydrophilicity,chemical composition and adhesive strength between PP film and PA6 film.2.Xylene was used as the swelling agent of surface and N,N-dimethylformamide(DMF)was used as the absorbing medium of microwave,the process and mechanism of microwave irradiation-induced grafting MAH onto PP film were explored.Compared with the traditional heat-induced grafting method,microwave irradiation could promote the decomposition of peroxides,effectively shortened the reaction time,and would not affect the mechanical properties and crystallized properties of the PP film.The conditions of the grafting process in organic solutions were optimized,and it was found that in the mixed solvent of xylene/DMF(2/1),when reaction time was 30 min,reaction temperature was 85?,concentration of MAH was 0.03 g/mL and concentration of BPO was 0.004 g/mL,the adhesive strength of modified PP film and PA6 film could reach up to 8.0 N/15 mm.3.Water was used as solvent and trace xylene was used as interfacial agent,the process of microwave-induced grafting MAH onto PP film was investigated.The results showed that the introduction of interfacial agent could quickly wet and swell the surface of PP film,which would provide more places for the grafting reaction and promote it.By dissolving the initiator BPO in interfacial agent,the efficiency of grafting reaction was improved.By introducing the comonomer styrene(St),the amount of grafted MAH increased.In aqueous solution with the addition ratio of xylene was 1/40,when reaction time was 30 min,reaction temperature was 80?,concentration of MAH was 0.03 g/mL,concentrations of St and BPO in xylene were 0.04 g/mL and 0.004 g/mL respectively,the adhesive strength of modified PP film and PA6 film could reach up to 13.3 N/15 mm.Compared with the microwave-induced grafting reaction in organic system,the modified PP film obtained in aqueous system has no monomer residue on the surface and better adhesive properties. |
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