After 50 hrs. irradiation, degradation increased with LM concentration in composites regardless the DE of CL20 .This may be either due to the sensitization effect of MA functional groups or the generation of free radicals during mixing of peroxide for MA grafting, those may further propagate the degradation in comparison of neat films. This tentative conclusion was confirmed by studying the behavior of ‘A’ series where degradation increased (< neat PE) with LM content after 50 hrs. as DE was almost same.
Here, it may be concluded that the exfoliation, intercalation and microcomposites nature is a recessive factor in comparison of maleation extent to decide the fate of polymer at 60°C under UV light in presence of air under longer UV treatment and samples shows more stability as soon as we move toward microcomposites. All composites were highly degradable and reached to the brittle point earlier than neat film after 150 hrs of irradiation. MA functionalized polymer (without clay) was more degradable than the one filled with CL20. This indicates that the presence of clay, in any form (microcomposites or nanocomposites), inside the matrix may protect the degradation under UV light up to some extent and nanoscaled dispersion of clay increases the induction period of samples and degradation initiate with delay. Thus DE of filler affects the induction period whereas, LM concentration affects over all fate of composites for 150 hrs UV exposure.
2 4 6 8 10
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Intensity (au)
2 Theta (Deg.) f
Figure 5.3. Increase in carbonyl region upon photoirradiation for ‘b’ (90/10, LM/LP) composites
Figure 5.4. Increase in carbonyl region upon photoirradiation in presence of air for neat polymer samples
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A b sor b ance
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A b sorban ce
Wavenumber (cm-1)
The SEM of ‘b’ showed a highly cracked surface in comparison of microcomposites ‘i’
after 150 hrs irradiation at lower and higher magnifications (Figure 5.5a1, 5.5a2 &
5.5c).The surface erosion decrease as soon as LP concentration increase as can be seen from SEM of ‘c’ (Figure 5.5 b).In previous attempts [9,10] such kind of behavior (higher stability of nanocomposites for initial UV irradiation) of polyolefin nancomposites during oxidative degradation could not be observed and the effect of dispersion state (either nancomposites or microcomposites) on degradation was not appeared conclusive. The most probable argument for this behavior must be the slow oxygen diffusion through matrix due to the increased diffusion path in presence of clay. The nature of matrix decide the oxygen diffusion and the degree of packing of chains decrease the number and size distribution of preexisting voids or holes, since chains are sandwiched between the clay surface ,restricting the mobility. The formation of low molecular weight photoproducts is more likely to occur in the case of polymers that have short branched reactive groups and further enhanced the degradability o polymer matrix [25].
The stability was evident from surface morphology also after careful observation of SEM of sample ‘j’, a microcomposite, where slight cracked surface was found and there were no change on the surface of ‘b’ after 50 hrs. irradiation. (Figure 5.6a & 5.6b). It is worth to recall that sample ‘j’ contain less amount of LM (which is highly sensitive to UV light) even it underwent more degradation than nancomposites ‘b’ (having more LM concentration) after 50 hrs. Thus initially, barrier effect of nanoclay prevent the degradation and overcome the LM induced photodegradation. This fact was eliminated for longer UV irradiation of samples and degradability increase with LM concentration. The sudden increase in degradability or decrease in stability after 50 hrs exposure to UV light for exfoliated and intercalated samples may be explained as follows: i) The chance of intramolecular propagation increases, as neither chains nor oxygen can move freely throughout the matrix as in the neat films or phase separated composites. This restricted motion may generate in chain carbonyl group via case formation (the hydroperoxide group may abstract labile atom i.e. tertiary bonded hydrogen at carbon atom generating an intermediate bi radicals which subsequently gives a carbonyl group), which is further helpful to propagate the degradation ii) Another cause may be the nature of termination reactions during degradation those can again generate the free radicals. Nanocomposites must follow the II c path preferably in comparison of II a and II b (Figure 5.7) because oxygen pressure inside the matrix should be higher than the micro and neat samples as oxygen can not come out so easily from matrix. Further it was supported by the presence
of oxides in ‘A’ series exfoliated nanocomposites (II d & II e), which probably generates in oxygen rich environments and possibly, when peroxy radicals would be present at neighboring position.
Figure 5.5a1, 150 hrs. irradiated nanocomposite of series ‘A’ (samples ‘b’,90 /10, LM/LP)
Figure 5.5 a2, 150 hrs irradiated nanocomposite of series ‘A’ (samples ‘b’90 /10, LM/LP) at higher magnification
Figure 5.5 b,150 hrs irradiated nanocomposite of series ‘A’ (samples‘c’,80 /20, LM/LP)
Figure 5.5c, 150 hrs irradiated microcomposite of series ‘D’ (sample ‘i’, 20 /80, LM/LP )
Figure 5.6a, 50 hrs irradiated nanocomposite of series A (sample ‘b’90 /10, LM/LP)
Figure 5.6b, 50 hrs irradiated microcomposite of series ‘D’ ( sample ‘j’ 10 /90, LM/LP)
Figure 5.7.Different termination reactions (II a to II c) and formation of different species resulting from combinations of peroxy radicals (II d & II e)