Research On Preparing Stable Co-Continuous Polyethylene/Polyamide6Blends Through Reactive Blending

Unlike droplet-matrix polymer blends, each component in co-continuous polymer blends is continuous and interlocks with each other, which confers this type of alloys brilliant prospects in the field of conductive polymer composite materials, biological tissue engineering, multi-porous membrane, controlled drug release and so on. Unfortunately, the innately awful instability and difficulty to manufacture cast a shadow over its future.In our previous article, based on self-assembly theory we innovatively employed two kinds of graft copolymers supplied into70/30(wt%) polyethylene(PE)/polyamide6(PA6) blends that were maleic anhydride(MAH) functionalized PE with long backbone length (MAH%=lwt%) and polybutadiene(PB) with short backbone length(Mn=3000g/mol, MAH%=10wt%) respectively, and consequently a robust co-continuous morphology was generated that could sustain annealing at235℃(higher than the melt temperature of PA6) for approximately15minutes. Formic acid solvent extraction experiments combined with SEM analysis demonstrated that the PA6minor phase was fully continuous. Besides, DSC cooling curves did not show fractional crystallization of PA6domain, a second plateau occurred between150℃to200℃in the curve of elastic modulus temperature dependence during DMA test, both of which also indicated existing of full continuous PA6phase.In this thesis, morphology evolution of these composite compatibilized PE/PA6blends as a function of compatibilizer concentration was quantitively investigated through SEM joint with selective solvent extraction experiments. It was found that at a given value of PB-g-MAH,5.6wt%, the most suitable content of PE-g-MAH for producing co-continuous structure in these blends landed in the range between9.7wt%and16.1wt%. When at a given value of PE-g-MAH,12.6wt%, just a little of PB-g-MAH addition would bring substantial development of co-continuity for these blends, and when the content of PB-g-MAH arrived at3.5wt%or above, these blends would stay at co-continuous morphology. On the other side, the total content of the composite compatibilizers also should be kept in a moderated range to generate co-continuous morphology. In summary, not only the single item value of the graft copolymers but also the total value of the composite compatibilizers must be required in a somewhat interval so as to induce co-continuous morphology in these composite compatibilized PE/PA6blends. The mechanism corresponding to the above results was proposed like this:on one hand, the PB-g-PA6generated through reaction between MAH groups of PB-g-MAH and amino groups of PA6was inclined to form a flat interface due to its short backbone, which meaned the PA6minor phase was dispersed in thread shape, but the interface was not stable enough if only PB-g-PA6existed. On the other hand, PE-g-PA6brought outstanding compatibilism effect. Although it compensated the stability of PA6fibrils, it also spontaneously bended the interface, formed sphere shape of minor phase, which was not favorable for coalescence of minor phase at lower content. Only when the concentrations of the two compatibilizers were matched in appropriate ratio, stable and flat interface would be maintained simultaneously. Moreover, the interface was not locked down completely, plus the concentration fluctuation of the composite compatibilizers, the PA6fibrils could coalesce in somewhat local area of interface, finally, a moderately stable co-continuous morphology was produced in these composite compatibilized70/30(wt%) PE/PA6blends. All in all, the premise to produce co-continuous structure in compatibilized polymer blends was to create an interface with vanishing curvature radii, and the interface should be situated in a balance between stability and flexibility.In order to further promote the stability of co-continuous structure in these composite compatbilized PE/PA6blends, nano organclay(o-MMT) was added through three discrete orders, namely (I)PA6/o-MMT was priorly prepared before blending with polyolefin,(Π)a materbatch of polyolefin/o-MMT was first prepared and then compounded with PA6pellets,(Ⅲ) o-MMT, polyolefin and PA6were simultaneously mixed. The results showed o-MMT had a detrimental effect on the formation of co-continuous morphology in these nanocomposites no matter what the blending sequence was, the previous co-continuous morphology in PE/PA6blends without o-MMT was totally degraded to sea-island type when o-MMT adding at a concentration of2.5wt%of PA6phase. SEM images united with DSC analysis confessed that the PA6phase existed both in fiber shape and sphere shape, in which the PA6fibrils could support themselves to some extent and dispersed PA6droplets suffered significant crystallographic confinement. It was indicated that o-MMT addition didn’t bother the interface architecture very much, so the PA6fibrils were generated as normally. Nevertheless, there must be a part of o-MMT migrating to the interface which disturbed fibrils coalescence process. Hence, the final morphology of PE/PA6/o-MMT composites was suspended at the fiber-matrix type.In addition, with regard to the confused condition of selective solvent extraction experiment which was used to provide semi-quantitive co-continuity degree of polymer blends, the influence of temperature on the sample weight loss during selective solvent extraction experiments was focused.70/30(wt%) PE/PA6blend with typical droplet-matrix morphology was taken as an example and formic acid was chosen to be the exclusive solvent for PA6. This sample was tested at room temperature,50℃and100℃, respectively. Surprisingly, results showed the sample weight loss continued to increase with extraction time going on and finally reached100%loss of PA6at heating condition, although the sample weight was kept unaltered at room temperature extraction. The reality of this phenomenon was confirmed by SEM, DSC and FTIR. Further, the weight loss-temperature dependence was certified in dispersed PE/PS and PE/PMMA blends, both of the results were same as the one above reported, which demonstrated this phenomenon was a universal case for polymer systems. So the best temperature condition for selective solvent extraction experiments was no heating. And in this thesis, all the formic acid extraction experiments were carried out in the condition of room temperature.