Electron Beam Induced Graft Modification Of Poly(ethyleneterephthalate)(PET) To Improve Flame Retardant And Anti-dripping

Polymer modification is one of the focus of research in polymer field, it also has important significance for industrial. PET material has become one of the most widely used polymers due to its excellent performance, but it needs to be modify owing to polymer disadvantage and high using requirements. Electron beam(EB) radiation is a more convenient and efficient technique, its application in the graft modification of polymer is increasing rapidly. In this paper, in order to improve flame retardance and anti-dripping performance of PET, high energy electron beam has been used to modify the PET material with appropriate monomer.Firstly, radiation effects of PET under EB have been studied in this paper. Certain performance parameters were tested such as breaking strength, elongation at break, molecular weight. And Atomic force microscope(SPM), photoelectron spectroscopy(XPS), X-ray diffraction(XRD) and thermal gravimetric analysis(TGA) were characterized after EB radiation. The results showed the degradation mechanism of PET under EB irradiation in the atmosphere: 1) After EB irradiation, breaking strength and elongation at break were decreased, and mechanical properties were become worse; 2) PET molecular weight and thermal stability were gradually declined due to electron beam radiation dose increasing, it indicated that PET macromolecular chains appeared radiation-induced degradation; 3) Based on the XPS spectra, the degradation of PET under EB followed by NorrishⅠtype mechanism, and released CO, CO2 gas; 4) The surface of PET became roughness after EB radiation by SPM image; 5) Through X-ray diffraction(XRD) analysis, the thermal effects with low dose of electron beam radiation can result in raising the degree of crystallization of PET; and the high dose of the electron beam radiation can result in degradation of PET. Since the regular structure was destroyed, the degree of crystallinity decreased.Secondly, after Acryl acid(AAc) induced grafting on the PET by co-irradiation method with EB, then evaluated PET-g-AAc properties in terms of thermal property, combustibility and structure. The results showed that degree of grating(DG) has the highest up to 22.3% under followed condition: radiation dose 400 kGy, monomer concentration 40%, FeSO4 concentration 0.1g/L, pretreatment last 2h at 85°C. SEM and FTIR studies confirmed that AAc was successfully grafted onto the PET. By comparing the mechanical properties of PET before and after the grafting, the breaking strength was increased and the elongation at break was decreased with the increasing of DG. Compared with normal PET, the thermo-gravimetric performance of PET after grafting has been significantly changed, the weight loss process became complicated, it mainly has five phases caused weight loss: 1) In the stage of 50°C to 160°C due to water vapor; 2) In the stage of 160°C to 247°C due to dehydration carboxyl anhydride formation; 3) Branched chain scission at maximum temperature 314 °C; 4) Polymer main chain was broken over 377°C; 5) PET charring caused by weight loss when the temperature exceeded 450°C. However, the limited oxygen index(LOI) value of grafted PET was decreased with increasing of DG, but the anti-dripping performance of grafted PET was improved significantly. DSC analysis showed the crystallinity of the grafted PET was decreased, because PAA after grafting destroyed the crystalline structure of PET. It indicated that AAc penetrate into the interior of PET. After electron irradiation reaction, the crystallinity of PET slumped as a result of destroying the original crystalline structure. NMR analysis showed that tertiary carbon atom increased greatly, the reason for this phenomenon should be that the crosslinking occurred on the sample after grafting. TEM analysis showed that densification of grafted PET fiber became lower; it indicated grafting and crosslinking of AAc have occurred in the skin layer of PET.Thirdly, after Acrylamide(AAm) induced grafting on the PET by co-irradiation method with EB, then evaluated PET-g-AAc properties including anti-dripping property, combustibility and structure. The results show that degree of grating(DG) has the highest up to 7.8% under followed condition: radiation dose 400 kGy, monomer concentration 40%, FeSO4 concentration 0.1g/L, pretreatment last 2h at 85°C. DSC results showed that grafting with AAm has little impact on the crystal structure. With DG increasing, the breaking strength was increased and the elongation at break was decreased. And compared with normal PET, PET-g-AAm added one weight loss curve between 180°C to 313°C as a result of branched chain decomposition, cyclization and condensation of amino group. With the improvement of grafting rate, flame retardance of PET gradually increased. However, there is always dripping droplet phenomenon no matter how much the DG is.Finally, PET has been first endowed flame-retardance and anti-dripping properties with AAc/AAm monomer grafting onto PET by co-irradiation method with EB. The results showed that: 1) Parameters screening of two monomers grafting has the same regular with single monomer. The synergistic effect of two monomers can significantly improve the DG to 36.7%; 2) Thermal stability of PET has been improved after grafted, while showing sum of AAm and AAc grafted separately; 3) Flame retardance and anti-dripping performance of PET have been improved with mixed monomers grafted through the results of flame test and SEM analysis of residual char. When the DG reached to 36.7%, LOI is 27.3, continued vertical burning time 5.5s, no smoldering, length of char is 114 mm, and no dripping phenomenon; 4) The weight loss process of PET has been significantly changed after grafting with AAc/AAm, including water vapor, dehydration carboxyl anhydride formation and branched chain scission; 5) Analyze grafts location whether in PET surface or inside combined with DSC result.Based on these results, this paper proposed model of radiation-induced grafting reaction by EB, explained electron beam radiation-induced graft was a radical polymerization from several aspects conclusion, analyzed the properties of grafted PET and described polymerization process of liquid phase in one-step under irradiation-induced grafting systematically. Then char formation mechanism has been proposed.Above studies and results showed that it was feasible and effective to develop flame-retardant and anti-dripping fabric by introducing concepts and methods of radiation-induced grafting with EB.