PLA matrix

In the thermal studies conducted by Song et al. (76), the Tg increased modestly with the addition of pure and carboxylic-functionalized MWCNTs in PLA matrix. Also, the T and Tm of the nanocomposites were found to be lower than pure PLLA. Tsuji et al. (63) also observed the same trend of decreasing T in the nanocomposites compared with pure PLA however, here the nano-fillers are SWCNTs. In addition, several studies reported the Tg of the nanocomposites was lower than that of pure PLLA (61, 63,65). 

Figure 7(c) shows the phase stmcture of the blend polymer composed of EBR/PLA (15/85 wt%). Macro-phase separated EBR domains in the PLA matrix were observed. By adding 5 wt% of PE-/ -PMMA (PMMA contents 75 wt%) to EBR/PLA (10/85 wt%) as a compatibilizer, finely dispersed EBR domains are observed in Figure 7(d). As a result, this polymer indicates very high Izod impact strength value (378 J/m) vis-a-vis the blend polymer s value... 

The crystallization of the PLA matrix induces a decrease in the carbon dioxide permeability coefficient [123, 132]. According to Sawada et al, [128] the effect of crystallinity on CO permeability is similar to the one on oxygen, that is to say there is a slight increase in the diffusion coefficient at low crystallinity followed by a decrease of 40%, whereas solubility decreases slowly in relation with the crystallinity degree. 

Furthermore, the effect of the temperature on measured water vapour permeability changes in function of the study. Auras et al. showed a decrease of the permeability with the temperature, whereas Shogren highlighted an increase [5,120]. Siparsky et al. [121] showed that the diffusion coefficients increase and the solubility coefficients decrease with the temperature at 90% RH, which is contradicted by Holm et al. who showed higher values of moisture sorption at a higher temperature [139]. The various and contradictory results show that the mechanism of water transport in PLA is not completely understood yet [5]. In particular the presence of water clusters in the PLA matrix and their potential to diffuse in cluster form are still controversial. 

Consequently, it appears that the L/D ratio of PLA influences the gas permeability but no conclusion can be reached regarding the water vapour transport in this pol)uner. Moreover, generally speaking, the crystallization of the PLA matrix makes it possible to decrease the gas permeability and the organic compound sorption in PLA. However, no agreement has been formed regarding the influence of crystallinity degree on water vapour transport in PLA due to the variety of PLA composition (L-lactic acid content) and measurement systems. 

Gauge length = 1 cm, elongation rate = 100 mm min Collagen-poly(lactic acid) (PLA) composites, 50% collagen fiber and 50% PLA matrix (w/w)... 

Audrey et al. [32] have studied on the introduction of talc into PLA. They revealed that the tensile modulus of PLA increased 92 % with 30 wt% of added talc. In this case flexural strength and flexural modulus of PLA also increased 14.5 and 196 %, respectively. Interestingly, their study also showed that 30 wt% addition of talc as a stiff additive to PLA has too little negative effect on impact resistance of PLA. They also reported 37.8 % increase in HDT of PLA matrix with 30 wt% addition of talc. 

In another study by Di et al. [47] revealed that the exfoliation of MMT in PLA matrix has been achieved due to the strong interaction between the MMT and polymer matrix. They also stressed that the high surface area of MMT layers had reduced molecular mobility of PLA leading to unique properties for the PLA/ MMT nanocomposites. The exfoliated MMT platelets act as nucleating agents at... 

Pluta [49] studied the structure and properties of PLA/MMT nanocomposites and showed an effective enhancement of MMT dispersion with prolongation of the blending time (from 6 to 30 min). They stressed that this was possible due to strong interaction between PLA-MMT and shearing forces during melt compounding. The nanostructure was induced by the intercalation followed by tactoids formation and exfoliation of MMT, as confirmed by TEM analysis and XRD. The studies performed also clearly revealed the influence of MMT s dispersion in the PLA matrix on the physical properties of the nanocomposites formed as the improved MMT s dispersion (at their constant concentration) had increased the thermal stability of the nanocomposites under oxidative and nonoxidative conditions was improved with MMT s dispersion. Besides that, the crystallization ability of PLA also improved with incorporation of MMT. 

Another study by Wu et al. [72] focused on the development of the PLA nanocomposites with various functionalized MWCNTs prepared by melt mixing for morphological, rheological and thermal measurements. The surface functionalization influences the dispersion state of MWCNTs in the PLA matrix strongly as the carboxylic functionalized MWCNTs show relatively better dispersion than that of hydroxy and purified MWCNTs, which is due to the nice affinity between carboxylic group and PLA. For all composites, no remarkable improvement in thermal stability is seen at the initial stage of degradation, while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the thermal depolymerization of PLA due to their barrier and thermal conductive effects, respectively. 

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