Weathering effect Weathering effect on the mechanical properties of PEO/PVA blends
Authors: Almashhadani Nahida Joumaa Hameed 
Published: July 2021

ABSTRACT

 Poly ethylene oxide PEO / Poly vinyl alcohol PVA  blends were prepared by cast method at different concentration (25%,30%,35%,40%,and 50%). Samples miscibility ,and thermal stability were studied  by using differential scanning calorimetry(DSC),and thermo gravimetric analysis (TGA) analysis. The results proved that there was one glass transition temperature for PEO/PVA up to 30% that was attributed to its miscibility. This miscibility associated with (Hydrogen  bonds) between (Hydroxyl group) in PVA, and PEO, whereas there were two glass transition temperature for the blends ratio more than 30%PEO,that was due its immiscibility. The results proved increase in (Tg) with PEO loading: whereas the melting point was fixed about(Tm=310Â°C). TGA results showed that  PEO loading caused overlapping between degradation stages ,and shifting in the second stage to higher degradation temperature, that was due to the good  PVA, and PEO compatibility, and thermal  stability improved of polymer blends. The mechanical properties of the samples  involved were studied :it was found  that  the tensile strength decreased with PEG ratio increase: whereas ,the elongation at break increased  with PEO ratio (PEO was used as a plasticizer to PVA).25% PEO/PVA proved  better tensile strength than the others blend ratios and elongation-at-break values in comparison with that ratio more than 25%,which was due  to good miscibility. These results were enhanced with optical microscope and FTIR analysis. 25%PEO/PVA was sellected to  study the UV-Weathering effect on the mechanical properties according to its ultimate strength(26.67MPa) in comparision with the blends envolved.The stress strain curves for 25%PEO/PVA before and after UV-Weathering with periods of time(25,60,and 90Hr.) showed little changes in ultimate strength up  to (60Hr) exposure time,then there were little decrese in ultmate strength in(90Hr) exposure time . Ultimate tensile strength decrease was attributed to premature failur induced by polymer photo degradation. UV-Weathering caused yelowish of  exposed samples that was due to long chain conjugated polymer sequencesbond formation induced by oxidative  photo degradation .This changes in polymer structure resulted in signficiant changes in aging behavior of  matrix material  (PVA). As results of photodegradation, carbonyl and hydroperoxides were formed. The results proved little changes within (60Hr),that was attributed to polymer stability.It was folowed by little changes in tensile strength and   the elongation at break decreased that was due to sample brittlence increase,which was induced  by irradiation ,that caused modulus of elasticity increase. It was experimentally observed that the  value of thermal conductivity of (PVA= 0.099W/cm.K).The results proved decrease in thermal conductivity with PEO loading increase.

Key words: DSC, FTIR, Mechanical properties, PEO/PVA , TGA, UV-weathering.

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