PETpla.net Insider 03 / 2015

MATERIAL / RECYCLING 21 PET planet insider Vol. 16 No. 03/15 www.petpla.net then rinsed twice with fresh water, dried to less than 50ppm moisture and injection moulded into 3mm thick plaques. Samples of flake from each of the exposure time periods was measured for IV (intrinsic viscosity) to determine if Solar UV caused any loss in molec- ular weight. The moulded plaques were also measured for IV, colour and haze. The data clearly shows that exposure to UV radiation was very damaging. Sample flake was measured for colour before and after the 12-month exposure to determine if any obvious yellowing occurred and it was found that the level of yellowing was not significant. It became so only after the weather-exposed PET had been subjected to the melting required for moulding the plaques. PET reclaimers extrude washed and cleaned flake into pellets, not plaques. If their bottles are stored outside and exposed to UV radiation, an increase in yellowness resulting from the extrusion process can be expected. Further yellowing will occur when pelletised rPET is blended with virgin PET resin and melted again, during preform manufacture. Sunlight exposure effects on the IV of PET Measurement of the cleaned and washed flake samples found decline in IV of about 0.04 dL/g over 12 months. This same molecular weight loss was seen when the weathered flake was injection moulded into the 3mm plaques. The degree of IV loss increased to ~0.06 dL/g when flake was melt-processed into 3mm plaques. Effects of sunlight exposure on PET colour and haze L* indicates the lightness of the sample: 100 is very white and 0 is black very dark. The injection moulded plaques made from weath- ered bottles show a definite reduction in L* over time. Virgin PET bottles will typically have L* values ranging from the high 80s to the low 90s. Bottles made with weather-exposed recy- cled PET will show a reduction in L* values; they are less clear to the eye and look duller. The diamonds on the graphs show the effect of two months’ exposure to fluorescent light, after the bottles were moulded into plaques. While they exhibited a measureable decrease in L*, direct sunlight had a much more significant and pro- nounced effect. 1 D. Hayward, The Effect of Contaminants on Yellowness in Recycled PET, APR presentation, Feb., 16, 2006 3 Jovan Radulovic, Degradation of Polyethylene Terephthalate in Natural Conditions, Scientific Technical Review, Vol. LVI. No. 2, 2006 4 S. Venkatachalam, Shilpa G. Nayak, Jayprakash V. Labde, Prashant R. Gharal, Krishna Rao and Anil Kelkar, Degradation and Recyclability of Poly(Ethylene Terephthalate), Reliance Technology Group, Reliance Industries Limited, B4, MDIC Industrial Area, Patalganga, Raigad District, Maharashtra State, India 5 Yu. S. Akishev, M.E. Grushin, A. I. Drachev, V.B. Karalnik, A.V. Petryakov and N.I. Truskin, The Open Plasma Physics Journal, 2013, 6,(suppl 1: M4) 19-29 b* denotes the degree of chro- maticity from yellow (+b*) to blue (-b*). The increase in yellowness on moulded plaques was very significant after only one month of exposure. Beyond three to four months the effects of UV, while still significant, were not as dramatic as during the ini- tial months. As was the case with L*, yellowness development was not as significant from the fluorescent light. The effect of the sunlight exposure on the haze of the molded plaques was minimal. The control plaque showed haze values of 9.9%, while the 12 month weathered PET haze dropped only to 9.5%. This study demonstrates that exposing bottles to sunlight in a humid environment can have a severe effect on the L*, b* and IV properties of recy- cled PET. Exposure to UV radiation, whether in external bale storage or even through exposure to fluorescent lighting in retail stores, should be con- sidered as another contributor to rPET quality degradation. www.plastictechnologies.com