A Study On Key Factors Which Effect On The Accelerated Testing Results Of The Thermal Oxidation Stability Of Polyolefine Resins For Hot-Water Pipe Applications

The thermal oxidation stability of four kinds of PPR resins for hot water pipe applications, which are PPR-4, TPC-5, PPR-2 and PPR-16, has been studied by use of fundamental experiment method(T=125 C ,d=0.5mm) based on the accelerated testing method developed by our laboratory. The critical water extraction time (twc) and the air oxidation time to rupture (tar) of four kinds of PPR resins have been achieved in fundamental experiment. The results show that twc and tar of PPR-4 are 75 h and 6 391 h respectively. twc and tar of TPC-5 are 431 h and 7 800 h respectively. The poor thermal oxidation stability of PPR-4 and TPC-5 is attributed to their short t wc. However, the residual antioxidant concentration in PPR-2 and PPR-16 test pieces after the longest prearranged water extraction time (tw 4 000h) is still so high that tw 4 000h is looked on as the conservative twc of PPR-2 and PPR-16. tar of PPR-2 and PPR-16 are 6 437 h and 4 008 h respectively. So, the good thermal oxidation stability of PPR-2 and PPR-16 depends on their long twc. The depletion process of antioxidants in the resins has been tracked by use of oxidation induction time (OIT) and infrared absorption spectra (IR). Therefore, the relation of In OIT-tw, In OIT-ta, ln I-tW, In I-ta can be achieved and studied after OIT and infrared absorption intensity I with relation to antioxidants are plotted against tw or ta in semi-logarithm coordinate. The results show that the poor resistance of antioxidants in PPR-4 and TPC-5 to water extraction is the main cause of theirpoor thermal oxidation stability. The antioxidant with ~3 650cm"1 absorbance band assigned to hydroxyl group in PPR-2 and PPR-16 has good resistance to water extraction, which provides substantial contribution for the good thermal oxidation stability of PPR-2 and PPR-16.The effect "of test pieces' thickness d on the result of accelerated test is studied by use of the comparison between the result of different test pieces' thickness (d= 1.0mm, 1.5mm, 2.0mm) and the result of fundamental experiment (d=0.5mm). And the effect of experiment temperature T on the result of accelerated test is studied by use of the comparison between the result at temperature 110C with the result at temperature 125C .The comparable items include twc, tar, and parameters of antioxidants' depletion kinetics. The results is as follows:1.Because of the improper pre-estimate of effect of d and T and improper experiment time arrangements according to the pre-estimate, no effective results have been achieved to further study, which show the effect of d and T on the accelerated test results is not so serious as we appreciated.2.There are four kinds of effect of d on parameters of antioxidants' depletion kinetics. Firstly, considering experiment error and fitting error, the effect of d on some parameters of antioxidants' depletion kinetics is not confirmed. For example, the slope P water,i and tw at knee-point in Inl36so-tw figure of PPR-2. Secondly, the effect of d on some parameters of antioxidants' depletion kinetics is illegible. For example, the slope P water2 in lnI365o-tw figure of PPR-2. Thirdly, the effect of d on some parameters of antioxidants' depletion kinetics is obvious. For example, the relative absorption intensity I at knee-point in Inl365o-U figure of PPR-2. Lastly, the effect of d on some parameters of antioxidants' depletion kinetics is abnormal. For example, the slope P waier in Inl365o-tw figure of PPR-16.3.The antioxidants' depletion at temperature 125 C is quicker than that at temperature 110C. For PPR-2, k,water is the ratio of P water2 (125C) to P water2 (110C). kMir is the ratio of P air (125C) to P air (110C). The average ks,waterand the average kg,ajr are 1.8 and 3.3 respectively. Similarly, for PPR-16, k,water is the ratio of P waler (125C) to P waler (110C). kMir is the ratio of Pair(125C) to air (110C). The average kBjWater and the average k,air are 2.2 and 2.6 respectively. The effect of temperature is obvious. But with comparison with 4 times calculated according to Arrhenius equation and temp...