| Atmosphere has an important influence on the thermal stability of general purpose plastics,such as inert gases and air.As one of the cheap and widely used polymer materials,the thermal stability and thermal degradation of PVC in different atmospheres are less paid attention to.Therefore,in this paper,we prepared PVC/dioctyl terephthalate(DOTP)/organotin(OT)/calcium zinc(Ca-Zn)/dipentaerythritol(Dip)and PVC/dioctyl terephthalate(DOTP)/organotin(OT)/calcium zinc(Ca-Zn)/dipentaerythritol(Dip)/butyl titanate(BT)/nano titanium dioxide(NT)respectively.The PVC films were characterized by X-ray diffraction(XRD),Raman spectroscopy(LRS),Fourier transform infrared spectroscopy(FTIR),Thermogravimetric infrared analysis(TG-FTIR)and thermomechanical properties(DMA).The thermal stability and thermal degradation kinetics of the films under different atmospheres were investigated by means of Congo red and thermogravimetric techniques.A possible thermal degradation mechanism model is proposed.And draw the following conclusions:1.Diffraction analysis showed that when 20=25.8°,the average microcrystalline size of BT/NT particles decreased by 2.70 nm compared with that before modification,which inhibited the agglomeration of nanoparticles.However,the NT characteristic peak was maintained significantly,and the BT ester group had a strong interaction with NT.FTIR indicated that BT ester group and titanium oxide formed a carbonyl titanium complex after the reaction.The energy storage modulus of NT modified by BT increased by 29.7%,which had a significant synergistic effect on the composite film.TG-FTIR analysis showed that after adding OT at 0.5 phr,Ca-Zn at 0.5 phr and Dip at 1.0 phr,the composite flm was around 331.1℃ and 476.6℃,and the peak strength of CH4 gas released by thermal degradation was 114.0 and 262.0%higher than that of blank sample,respectively.It can be seen that pentaerythritol has a promoting effect on CH4 release of PVC,and the peak strength of CO2 is shifted to the high temperature zone,contrary to the blank sample,there is no formation of hydroxyl or water,which means that the thermal degradation pathway of PVC has changed,and it is possible to inhibit the generation of aromatic hydrocarbons and dioxins.2.When the ratio is PVC/DOTP/OT/Ca-Zn/Dip(100/50/0.5/0.5/1.0 phrs),the thermal analysis under air atmosphere shows that the thermal decomposition process goes through three stages,β=10℃/min,180.5-372.6,372.6-489.6 and 489.6-600.0℃,respectively.Among the non-model methods,the average apparent activation energies of Friedman,FWO and KAS in the first,second and third stages are 206.56,90.22 and 155.58 kJ/mol respectively.By using the model method and the theoretical master diagram method,the Second-order reation(F2)mechanism model of the first stage thermal decomposition was obtained.The differential mechanism function is f(α)=(1-α)2,and the integral mechanism function is g(α)=(1-α)-1-1.3.The thermal analysis in the nitrogen atmosphere as above shows that the thermal decomposition of the film goes through two stages,which are 199.0-364.4 and 364.4-513.7℃ respectively when β=5℃/min.The maximum value of residual carbides is 10.19%,which increases obviously compared with 0.48%in air due to thermal oxidation decomposition.Among the non-model methods,the average apparent activation energies of Friedman,FWO and KAS in the first and second stages are 119.18 and 228.76 kJ/mol respectively.According to the model method and the theoretical master diagram method,the thermal decomposition of the thin film in the first stage conforms to the One and a half-order reaction(F1.5)mechanism model,the differential mechanism function is f(α)=2(1-α)3/2,and the integral mechanism function is g(α)=1/(1-α)1/2-1.4.When the ratio of PVC/DOTP/OT/Ca-Zn/Dip/BT/NT(100/50/0.5/0.5/1.0/1.0/5.0 phrs),the film had the best thermal stability in the Congo red test,and the initial and complete blue turning time were the longest.The thermal decomposition of different films in air shows three stages.The thermal decomposition of the film atβ=10℃/min is 195.7-382.7,382.7-500.0 and 500.0-588.5℃,respectively.The average values of the first,second and third stages of Friedman method,FWO method and KAS method were 225.33,278.62 and 82.95 kJ/mol,respectively.According to the model method and the theoretical master diagram method,the thermal decomposition of the thin film in the first stage conforms to the Third-order reation(F3)mechanism model,the differential mechanism function is f(α)=(1-α)3,and the integral mechanism function is g(α)=[(1-α)-2-1]/2.5.The thermal decomposition of the films in nitrogen shows that the thermal decomposition process can be divided into two stages at different heating rates.Whenβ=10℃/min,the two stages are 188.3-382.1 and 382.1-527.9℃,respectively.The maximum carbon residue of 15.45%increased by 349%compared with 3.44%in air atmosphere,indicating that oxygen has an important effect on the degradation of PVC.The average values of Friedman,FWO and KAS in the first and second stages were 136.16 and 230.35 kJ/mol,respectively,for the non-model method.Using model method and theoretical master diagram method,it can be seen that the first stage of thermal decomposition of the thin film conforms to the Second-order reation(F2)mechanism model,the differential mechanism function is f(α)=(1-α)2,and the integral mechanism function is g(α)=(1-α)-1-1.Figure[39]table[29]reference[89]... |
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