Summary: Within the present study FTIR and Raman spectroscopy are evaluated as to specific strengths in terms of analysing deterioration in TPU induced by UV radiation or thermal load. A conventional ester based TPU grade formulated from 4,4'-methylene diphenyl diisocyanate, 1,4-butanediol and polycaprolactone was investigated. Exposure to UV was done in a Suntest CPSþ at different exposure times. Thermal treatment was done in an air circulation oven at 180 C and different exposure times. Exposed samples were characterized as to changes in molecular structure with complementary methods ATR and Raman spectroscopy. To establish interrelationships between structural changes and macroscopic material characteristics UV/Vis/NIR spectroscopy and DSC were applied.UV/Vis/NIR spectroscopy clearly indicated yellowing, and thus an increase in absorption in the visible wavelength range, of TPU after exposure to UV or to thermal load. Yellowing correlated well with formation of chromophoric groups detected by ATR and Raman spectroscopy. ATR spectroscopy turned out to be very sensitive in detection of changes in chemical structure induced by UV radiation. Raman spectroscopy was found to be very sensitive in detection of changes in chemical structure induced by thermal load. No distinct effect of UV exposure on morphology of TPU was ascertained. In contrast, a strong effect of thermal treatment on (para)crystalline morphology was observed.

Within this study, the applicability of Raman spectroscopy to characterize the crystallinity of PLA staple fibers was evaluated. The influence of the fiber alignment on the possibility to detect crystallinity by using Raman spectroscopy was studied. PLA staple fibers were produced by melt spinning by varying both draw temperature and draw ratio. Systematic interrelationships between the processing parameters of PLA staple fibers and the degrees of crystallinity and the cold crystallization enthalpies were established. Raman spectroscopy showed that the carbonyl stretching band of Raman spectra measured in fiber axis and parallelly polarized was not sensitive to detect crystallinity. However, for perpendicularly polarized measurements, a higher sensitivity was observed. With increasing degree of crystallinity, a reduction of the band width of the normalized carbonyl stretching band was found. The morphology affected the mechanical properties significantly. Increased draw ratio resulted in increased tensile strength and decreased elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42432.

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Abstract:The focus of this work is on interfaces of two-shot molded parts. It is well known that e.g. material combination, process parameters and contact area structures show significant effects on the bond strength of multi-component injection molded parts. To get information about the bond strength at various process parameter settings and material combinations a test mold with core back technology was used to produce two-component injection molded tensile test specimens. At the core back process the different materials are injected consecutively, so each component runs through the whole injection molding cycle (two-shot process). Due to this consecutive injection molding processes, a cold interface is generated. This is defined as overmolding of a second melt to a solidified polymer preform. Strong interest lies in the way the interface conditions change during the adhesion formation between the individual components. Hence the interface conditions were investigated by computed tomography and Raman spectroscopy. By analyzing these conditions the understanding of the adhesion development during the multi-component injection molding was improved.

Summary: A fracture surface investigation was conducted to study the applicability of cracked round bar (CRB) specimens for an accelerated extrapolation concept for a lifetime assessment of polyethylene (PE) pipes. Scanning electron microscopy and topography metrology with InfiniteFocus were used to study the slow crack growth behavior in CRB specimens at different loading conditions. The results confirm the compliance of the CRB test with the requirements of linear elastic fracture mechanics.