Development And Application Of Pentaerythritol Esters Heat Stabilizer For Rigid PVC

Due to its own defects and the high temperature and shear conditions during processing,PVC must add a lot of auxiliaries in the application process,of which the thermal stabilizer is the most important one.Thermal stabilizers mainly include main stabilizers and auxiliary stabilizers,and polyols are widely used as one of auxiliary thermal stabilizers.There are many researches related to the use of other main stabilizers in PVC.Modifications such as salting,esterification and subsequent application of composites have also been reported.However,there are not many report about systematically studying the effect of hydroxyl content after esterification on the effectiveness of the composite application.This dissertation mainly focuses on the esterification of pentaeryth ritol,using three different carbon chain length linear carboxylic acids:stearic acid,palmitic acid,myristic acid,and exploring the carbon chain length and esterification of the hydroxyl content of pentaerythritol esters respectively.Complex application with calcium stearate and zinc stearate.By adjusting the acid-alcohol ratio to control the hydroxyl content,the synthesized product was applied and then the synthetic process of the better product was investigated.The thermal stability of PVC can be characterized using Congo red method,thermal oven aging method,differential thermal analysis method,ultraviolet spectrophotometry and torque rheometer method.For the synthesis process,the effects of temperature,reaction time,amount of water-carrying agent,type and amount of catalyst on the progress of the reaction are mainly investigated.This dissertation draws the following conclusions through a series of experiments.1.by comparing the three kinds catalysts of phosphoric acid,toluenesulfonic acid,concentrated sulfuric acid and glacial acetic acid mixture for the reaction of the esterification according to the catalytic situation,select the Ts OH as the catalyst.Ts OH was used to catalyze the esterification reaction of pentaerythritol with stearic acid,palmitic acid or myristic acid respectively,the four corresponding products were obtained.FTIR showed that the pentaerythritol esters all had characteristic peaks n ear1730 cm^-1.By analyzing the synthesized pentaerythritol esters by TGA,we found that under the same weightlessness,the corresponding weight loss temperature generally showed an increase with the molecular weight,indicating that the corresponding pentaerythritol esters were the aimed products.And weight loss temperature is all above220°C,higher than the processing temperature of PVC,indicating that the synthetic products can be used as PVC additives,in addition to the esterification of pentaerythritol melting point are around 60°C,lower than its own melting point of 261°C,is conducive to it can be fully dispersed in PVC.After the reaction products were applied separately,the relatively better three formulations including the products of PETS1,PETP1,PETM1respectively.Based on the investigation of the synthetic process of these three products,the following conclusions were drawn:the optimum amounts of catalyst and water-receiving agent are respectively 0.25%and 10%of the total mas s of the reaction raw materials;the optimum reaction temperatures of pentaerythritol with stearic acid,palmitic acid and myristic acid were 170°C,150°C,and 140°C,respectively.The optimum reaction time was 90 minutes.2.The Congo red experiment showed that Ca St₂/Zn St₂ produced good synergistic effect with pentaerythritol ester and prolonged with the addition of pentaerythritol ester.Withtheincreaseofhydroxyesterificationrate,theheatstabilitytime decreased,indicating that the hydroxyl content can promote the heat stability time.Thermal oven aging experiments show that the system of pentaerythritol esters improves both the initial whiteness and the long-term thermal stability of PVC.Compared the experimental results of thermal oven aging and the Congo Red composite of the formulation with the PETS4,PETP4,and PETM4 products,founding that the length of the molecular chain and the degree of entanglement affect the migration of the molecular chain,thereby affecting the timeliness of the participation of the ch aracteristic functional groups,and thus affecting the thermal stability.Through the torque rheometer experiment,we found that the addition of pentaerythritol ester made the PVC thermal stability time significantly longer than that of Ca St₂/Zn St₂,and the thermal stabilization time of Ca St₂/Zn St₂ was only 400 s,while the thermal stability time of the composite pentaerythritol ester was significantly improved.3.TGA analyzed the thermal decomposition of composite applications.The results show that the thermal degradation of PVC is divided into two stages,the first stage is the removal of HCl,the temperature is generally 250³20°C;the second stage is the carbon-carbon skeleton fracture and decomposition,the temperature is generally400⁵00°C.By comparing the decomposition temperatures before and after the composite pentaerythritol esters,it was found that the addition of pentaerythritol esters increased the decomposition temperature of the original CaSt₂/ZnSt₂ system.The solid-phase UV test of PVC samples found that:as the aging time increases,the absorption in the long wavelength direction gradually increases,while the absorption in the short wavelength direction does not change significantly,indicating that the degradation of PVC is mainly the increase of the number of conjugation sequences.4.The effect mechanism of pentaerythritol ester and Ca St₂/Zn St₂ was investigated through comparative experiments.Experiments show that Zn Cl₂ can catalyze PVC degradation,while PETM1 can effectively inhibit the catalytic effect of Zn Cl₂ on PVC.The Zn St₂/PETM1 system shows that Zn St₂ is the initial type of heat stabilizer;Ca St₂/PETM1 system shows no synergistic effect between Ca St₂ and PETM1,and Ca St₂ is a long-term thermal stabilizer.The addition of PETM1 can significantly improve the effect of Zn St₂/Ca St₂ in PVC.By investigating the torque rheological experiments combined with the three systems of PETS4,PETP4 and PETM4,it was found that the thermal stability time of the PETS4 system with the longest carbon chain is longer than that of the PETM4 system with the shortest carbon chain.It shows that the thermal stability of the longer carbon chain under the same system is better,its effective time is longer and more stable during the shear friction process.