热稳定剂对PVC紫外光老化过程中微观结构及宏观性能演变的影响

通过UV-Vis、FTIR、DSC、以及色差、力学性能的测试表征,实时追踪分析了在紫外光老化过程中,含Pb、Sn以及Ca-Zn热稳定剂的PVC体系微观结构和宏观性能的演变过程.结果表明,在相同光老化条件下,PVC/Pb、PVC/Sn和PVC/Ca-Zn体系的微观结构变化规律基本一致,过程中主要的化学反应是,大分子吸收光能后,发生脱HCl生成共轭双键的反应、生成羰基的氧化反应、交联反应和降解反应;不同热稳定剂的作用,主要表现在对于微观结构变化的幅度和动力学过程的影响不同.相应地,3种体系的外观色差和力学性能的变化规律也相似,但色差的变化程度和速度以及老化后力学性能的保持率因所含热稳定剂的不同而不同,其中含Sn体系的颜色稳定性最好,含Pb体系的力学性能保持率最高。

MICROSTRUCTURE AND PROPERTIES DEVELOPMENT OF THERMALLY STABILIZED PVC DURING PHOTOAGEING

Three different poly(vinyl chloride)(PVC) formulations were submitted to photo ageing.The influence of the different thermal stabilizers was evaluated by means of ultraviolet-visible(UV-Vis) spectra,fourier transform infrared(FTIR) spectra and differential scanning calorimetry(DSC).The gel content formed in exposed samples was estimated gravimetrically,and the color and mechanical properties changes of PVC during photoageing were studied.It was found that microstructures of three PVC/thermal stabilizer blends changed in the same tendency.As UV irradiation time increases,the conjugated polyene sequence,carbonyl group and the gel content increase,respectively.And the molecular weight decreases.Meanwhile,the yellowness index,the elongation at break and impact strength of the PVC sheets gradually decrease with increasing UV irradiation time.The main photochemical reactions include photo-dehydrochlorination,photooxidation,degradation and crosslinking.The degree and the kinetics of dehydrochlorination,oxidative,degradation and crosslinking during photoageing were different in three PVC /thermal stabilizer blends.Sn was the most efficient on restraining dehydrochlorination.Pb was the most stable in the reaction of oxidative degradation and crosslinking.As a result PVC /Sn blends showed higher color stability,and the retained percentage of impact strength and elongation at break of PVC /Pb blends were the highest among of the three blends.