Effect of the Recycled HIPS Surface Yellowing Phenomenon on Its Properties

The paper investigates the effect of the degree of HIPS surface yellowness on its properties: colorimetric, surface, rheological, and mechanical. In order to prepare three naturally degraded samples, about 1 kg of white HIPS flakes, semi-yellow HIPS flakes, and yellow HIPS flakes, segregation based on colorimetric analysis was applied. Then, these samples were subjected to ATR-FTIR analysis, sessile drop contact angle measurements, and MFI analysis. These analyses were repeated for standardized specimens made of the segregated HIPS flakes. The average absorbances were determined for 50 HIPS samples of each type in the form flakes. Finally, mechanical tests were carried out on the standardized specimens. As follows from the research, yellowing of the HIPS surface affects the final color of the standardized specimens, which is confirmed by optical colorimetry. Moreover, material degradation demonstrated by yellowing of its surface and confirmed by a decrease in ATR-FTIR spectra absorbance, is associated with changes in mechanical and rheological properties, as well as in surface characteristics. The novelty of this study lies in the investigation of naturally degraded HIPS samples under laboratory conditions (the HIPS materials were not subjected to artificial aging using laboratory equipment), obtained from waste post-consumer cooling devices used in consumers’ homes, representing natural wear and tear of the material. The tests provide insight into both the visual and mechanical properties of components manufactured from recycled HIPS originating from degraded refrigeration equipment. They also constitute a valuable source of information for processors and manufacturers.