Preparation And Alkaline Corrosion Resistance Properties Of Modified Flexible PVC Films

Polyvinyl chloride(PVC)materials are widely used,and can be divided into rigid PVC(plasticizer content is lower than 10%),semi-rigid PVC(plasticizer content of 10%to 30%)and soft PVC(plasticizer content of 30%to 70%)according to the content of plasticizers(such as dioctyl phthalate,diisononyl phthalate,etc.).Soft PVC broadens the application range of PVC materials,prepared flexible PVC films have the characteristics of good processability,excellent toughness,and low cost.It is widely used in building materials,cables,packaging films and other fields.However,the commonly used flexible PVC materials are generally composed of PVC resin,plasticizers,fillers,and other components,which will inevitably bear the impact of special environments such as strong alkaline,resulting in a decline in their performance,even cause a series of safety accidents.Therefore,many researchers have done a lot of research work on the performance changes of PVC films in different environments,but there are few reports on how to improve the alkaline corrosion resistance of flexible PVC films.Firstly,in this thesis,the solution method was used to prepare PVC films.The effect of alkaline corrosion on the performance of PVC films was tested by a variety of characterization methods,and the physical and chemical structures changed of PVC films during the alkaline corrosion process were analyzed.The results of EDS and UV-Vis tests show that in the process of alkaline corrosion,the HCl removal reaction occurs inside PVC films,which leads to a decrease in the content of Cl element.At the same time,the increases of“n”value in(CH=CH)_n causes the chromatic aberration change of PVC films.Among them,the?E value of PVC films reaches 21.60when alkaline corrosion after 28 days,and the weight loss rate reaches 7.11%.The SEM results show that alkaline corrosion holes appear on the surface of PVC films.Secondly,the hot-pressing method was adopted to prepare flexible PVC films,the effects of plasticizers(diisononyl phthalate,DINP)and fillers(nano calcium carbonate,nano Ca CO₃)on the alkaline corrosion resistance of flexible PVC films were explored respectively,and the physical and chemical structure changes of flexible PVC films before and after alkaline corrosion were characterized.The results show that the flexible 70 phr DINP/PVC films after alkaline corrosion have a weight loss rate of 30.76%after immersion for 24 h,and the weight loss rate of PVC films is only 0.77%.At the same time,it is intuitively found from the SEM images that the surface corrosion of the flexible 70 phr DINP/PVC films are more severe.In addition,studies have found that the addition of DINP to the flexible PVC films accelerate the degree of alkaline corrosion,and the degree of corrosion becomes deeper with the increase of DINP content.Therefore,in same alkaline condition,the degree of alkaline corrosion of flexible PVC films are much greater than that of PVC films.The filling modification could slow down the degree of alkaline corrosion.Under the same alkaline corrosion condition,flexible 50 phr Ca CO₃/PVC films compare with flexible PVC films,the weight loss rate and dimensional shrinkage rate decrease from 13.99%and9.75%to 8.95%and 6.95%,respectively.The tensile strain retention rate also increases from 58.32%to 65.11%.Finally,the wet modification method was adopted,using hexagonal boron nitride(h-BN)as raw material and isopropyl tris(dioctyl pyrophosphate acyloxy)titanate as the modifier,so as to prepare the modified h-BN(Mh-BN).Then the flexible Mh-BN/PVC films were obtained by the method of hot pressing.In the end,the researchers analyzed by FT-IR,SEM,weight loss,and mechanical properties on Mh-BN and modified flexible PVC films.The results show that isopropyl tris(dioctyl pyrophosphate acyloxy)titanate is successfully grafted on the surface of h-BN,and at the same time,Mh-BN has a good dispersibility in PVC matrix and can be formed a dense"labyrinth"structure,which can block the corrosion of the flexible PVC films by alkaline solution.After alkaline corrosion,comparing with flexible PVC films,the weight loss rate of flexible Mh-BN/PVC films decreases from 13.33%to 8.16%,the dimensional shrinkage rate decreases from 7.54%to 5.17%,the?E value decreases from 16.35 to 4.99,and the retention rate decreases from 198.87%to 108.48%,and the tensile strain retention rate increases from 62.11%to 93.66%.Filling Mh-BN to modify flexible PVC films can inhibit the performance degradation of flexible PVC films during alkaline corrosion.