Biodegradable Nanocomposites from Toughened Polyhydroxybutyrate and Titanate-Modified Montmorillonite Clay

Abstract

Montmorillonite clay treated with neopentyl (diallyl)oxy tri(dioctyl) pyrophosphato titanate was used as a reinforcement for toughened bacterial bioplastic, Polyhydroxybutyrate (PHB) in order to develop novel biodegradable nanocomposites. The modified clay, PHB, toughening partner and specific compatibilizer were processed by extrusion followed by injection molding. Different microscopy and goniometry techniques, rheology analysis, X-ray diffraction and thermo-mechanical testing were used to characterize the nanocomposites. Results showed that the nanocomposites with 5 wt% titanate-modified clay loading exhibited about 400% improvement in impact properties and 40% reduction in modulus in comparison with virgin PHB. The novel aspect of the titanate-based modification was that the nanocomposites still maintained nearly the same impact strength value as that of toughened PHB. The diffraction patterns suggest exfoliation of the organically modified clays and this was further supported by transmission electron microscopy and melt rheological analysis. The mechanical properties of the nanocomposites were correlated with a modified Halpin-Tsai theoretical model and the predictions matched significantly with the experimental results. Toughened and compatibilized PHB showed significantly lower biodegradation rate than virgin PHB and most significantly the addition of the titanate-modified clay in the same formulation enhanced the biodegradation several fold.

PHA/Clay Nano-Biocomposites

“…As suggested by Sinha Ray et al [82], albeit with reference to PLAs, it is possible that the terminal hydroxyl groups on clay edges could bind water in the test environment and act as active sites for ester hydrolysis, thereby speeding up the process of biodegradation. As noted by Parulekar et al [43], the state of dispersion of nanoclays in a polymer matrix may also influence polymer chain fragmentation.…”

“…An example of research in this field is the work of Wang et al [81] in which the biodegradability of PHBV/OMMT in soil suspension decreased with increasing OMMT content. However, there are also reports indicating enhanced degradation rates in nanocomposites as, for example, in the study of titanate-modified clay as an additive in a toughened PHB matrix [43]. In this case, PHB and PHB compounded with an epoxidised natural rubber degraded at similar rates but faster than a combination of PHB with epoxidised natural rubber and maleated rubber.…”

“…Parulekar et al [43] prepared PHB in combination with an MMT modified with neopentyl (diallyl)oxy tri(dioctyl) pyrophosphate titanate and an epoxidised natural rubber toughening agent as an approach to overcoming the brittleness and fracture susceptibility of PHB. The purpose of adding the modified MMT was to compensate for the loss in modulus brought about by rubber addition and to provide materials suitable for structural applications.…”

“…Choi et al [41] adopted a melt-processing method in which PHBV was compounded with Cloisite Ò 30B in a Brabender mixer and these authors used XRD and TEM to demonstrate that intercalated morphology was achieved. Parulekar et al [43] claimed that well-defined exfoliated morphology was obtained when dispersing titanate-modified clay in a PHB toughened with epoxidised natural rubber and a maleated rubber and evidence was presented in terms of both TEM and melt rheological analysis. Similarly, Botana et al [44] used XRD and TEM to confirm that an intercalated structure had been obtained when melt compounding PHB with Cloisite Ò 30B in a Brabender Plasti-Corder Ò .…”

Application of Poly(hydroxyalkanoate) In Food Packaging: Improvements by Nanotechnology

“…As a rule, any factor which increases the hydrolytic tendency of PHAs may facilitate degradation 149 . Also, well-dispersed clay particles lead to more rapid fragmentation of the polymer and therefore increased degradation 150 . The presence of 2 wt % organo-modified fluoromica 147 and low temperatures increased the biodegradation rate of PHB.…”