Proposal and Rationale: Several changes are being proposed to the heat aging test. These are as follows, with rationale for each change: Test temperature addition, allowing both 240F and 275F. oTesting at 240F for the required time (see next section) takes a long time. This increases the chance of equipment malfunction, power failures, calibration drift etc. oMost manufacturers are currently testing at 275F using internal criteria (until D6878 is modified). oAn Inter Laboratory Study concluded that: The study consisted of running heat aging tests at two temperature levels 240 and 275 and on all procedures the higher temperature achieved an overall equivalent result accomplished at a much shorter time period. In some cases, particularly tensile, the performance over time was more consistent among the labs for the different materials at the higher temperature as well. oThe Inter Laboratory Study, considering visual inspection only (surface cracking), also concluded that: The times to fail at the two temperatures tested are highly correlated. Thus there is little difference in the performance of the tests using either the 240 or the 275. However, the higher temperature reached conclusion in as little as 4 weeks and in all cases ended by 13 weeks (just a little over 2 months) while tests at 240 needed as much as 52 weeks (a full year) to reach failure. Pass criteria to include visual inspection at 7x magnification with sample bent over a 3 inch diameter mandrel. oA known failure mode in the field has been surface cracking of TPO. oThe visual inspection aligns the heat aging with the UV weathering inspection. Pass criteria to include a maximum weight loss of 1.5%. oAn independent study by SRI into the heat aging of TPO at 275F found that the material undergoes very slow weight loss until a point where weight loss becomes rapid. That inflection point was at 1.5% and corresponds with loss of stabilizer. The weight loss up to that point is thought to be due to loss of moisture and low molecular weight waxes in the polymer. Physical property testing after heat aging has been deleted. oTPO roof failure due to a change in physical properties has never been observed. oThe ILS report on heat aging notes that significant differences existed between labs for some of the physical property values and changes, notably tensile strength. oThe correlation between physical property change and known roof failure modes such as cracking or erosion is unknown.
Keywordsflexible sheet; roofing; roofing material; single-ply roofing membrane; thermoplastic polyolefin; TPO;
Ballot Item Approved as D6878/D6878M-2017 and Pending Publication