Effect of UV exposure on the microstructure and mechanical properties of long fiber thermoplastic (LFT) composites
- 229 Downloads
In this work, the effect of ultraviolet (UV) exposure on the microstructure and dynamic Young’s modulus of polypropylene (PP)/21 vol.% E-glass LFT and neat PP was investigated. Microscopic observations revealed that the damage due to UV was confined to the surface region only in the form of surface cracking and exposure of fibers to the surface in the case of long fiber thermoplastic (LFT) and surface cracking in the case of neat PP. Fourier transform infrared spectroscopy showed that the crystallinity of PP in the damaged layer increased, both in neat PP as well as in LFT, with exposure time. This is due to chemicrystallization, which involves rearrangement of amorphous broken polymer chains into crystalline form. Crystallinity of PP in the damaged layer in LFT increased at a higher rate as compared to that in neat PP. Results of nanoindentation showed that the Young’s modulus of the PP in the damaged layer increased, with UV exposure time; the rate of modulus increase being higher in the case of LFT than in neat PP. Although the local Young’s modulus of the degraded layer increased, the dynamic Young’s modulus of the overall composite showed a decrease with UV exposure time.
KeywordsContact Stiffness Transverse Crack Flexural Modulus Continuous Stiffness Measurement Unexposed Sample
Financial support for this work was received from Federal Transit Administration (FTA), contract #AL-26-7022-02. Thanks are due to S.D. Bartus and S. Pillay for providing the LFT plates. Thanks are also due to K. Carlisle for helpful discussions.
- 7.Lundlin T, Falk RH, Felton C (2001) Proceedings of the 6th International Woodfiber-Plastic Composites Conference, Forest Products Society, May, Madison, Wisconsin, p 87Google Scholar
- 14.Simmons G, Wang H (1971) Single crystal elastic constants and calculated aggregate properties: a handbook. MIT Press, Cambridge, MAGoogle Scholar
- 15.Karger-Kocsis J (ed) (1999) Polypropylene: an A-Z reference. Kluwer Academic Publishers, The NetherlandsGoogle Scholar
- 16.ASTM E 1876–99 (1999) Annual book of ASTM standards. American Society for Testing and MaterialsGoogle Scholar