Blends of PLA

The application of PLA in the field of commodity plastics requires a dramatic reduction in the costs of this polymer, as well as reliable and controllable 

Stareh loading level plays a key role in determining the mechanical properties of PLA/starch blends. Tensile strength and elongation almost linearly decreased as starch content increased. Thus, starch is typically characterized as a solid filler (Ke and Sun, 2000). The tensile strength of the blends can be described by eqn 10.2 (Nicolais et al., 1971), on the assumption that the adhesion between starch granules and PLA matrix does not exist. 

The Young s modulus and dynamic storage modulus increased as starch concentration increased up to 70%. For example, a PLA blend with 50% 

Blend Tensile strength (MPa) Elongation at break (%) Modulus (GPa)  

Most polymeric blends are commercially compounded by extmsion. The functional groups should react to form the required concentration of graft or block 

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By introducing DXO units into the backbone of PLA, the Tg of the lactides may be lowered to or below body temperature, and the crystallinity may be lowered. Thus, more flexible materials are obtained where the properties and degradation rate can be varied over a broad range by means of the composition. This is interesting for biomedical applications. Blends of PLA and PDXO provide additional opportunities to vary the properties. There is a large difference in reactivity ratio of LA and DXO [154]. As a result, a more block-like copolymer structure than expected for a totally random copolymer is obtained, even though the structure is somewhat randomized by transesterification reactions. In contrast, DXO and e-CL form a truly random copolymer [156]. Tri-block copolymers of LA and DXO have recently been described [303]. 

For in vivo release studies, scleral plugs prepared from blends of PLA-70,000 and PLA-5000 at weight ratios of 80/20 and 25% of GCV were used. The scleral plugs containing GCV were implanted in pigmented rabbits. Animals were killed at days 1 and 3 and at weeks 1,2, 3,4, 6, 8, 10, 12, 14, 16,18,20, and 24 after implantation, and the eyes were enucleated. Five rabbits were used at each time point. The intravitreal GCV concentration was determined by high-performance liquid chromatography (HPLC). 

Figure 10 GCV concentrations in the vitreous after implantation of the scleral plug prepared from the blend of PLA-70,000 and PLA-5000 with a ratio of 80/20. The values are shown as mean SD. The shaded area indicates the ED50 range of GCV for CMV replication. Abbreviations. CMV, cytomegalo virus GCV, ganciclovir PLA, ploylactic acid PLGA, polyglycolic acid. Source From Ref. 4.

Blending of PLA with natural fibers such as kenaf is another possibility by which PLA can be converted to end products using slightly modified standard industrial machinery for thermoplastics... 

Zhang and Sun [211] used dioctyl maleate (DOM) as a compatibilizer in blends of PLA/starch. Using DOM as a compatibilizer markedly improved the tensile strength of the blend, even at low concentrations (below 5 %). When DOM functioned as a plasticizer at concentrations over 5 %, significant enhancement in elongation was observed. Compatibilization and plasticization took place simultaneously, which was indicated by the mechanical properties and thermal behaviour of the blends. With DOM as a polymeric plasticizer, thermal loss in the blends was not significant. Water absorption of PLA/starch blends increased with DOM concentration, whereas DOM leaching in an aqueous environment was inhibited. 

Table 11.2 Siunmary of reported mechanical properties for blends of PLA with PC...

The most widely studied polymer blends of PLA are those containing polyc-aprolactone (PCL). PCL is also degradable polyester and due to its low Tg it exhibits rubbery characteristics with an elongation at break of approximately 600 %, which makes it an ideal candidate for toughening PLA. However, immiscibility of PLA and PCL in binary blends, courses phase separation, and tends to lower the fracture properties and in generally lead to insignificant improvements in mechanical properties. Due to this drawback, current researches... 

Paul et al. [54] developed the plasticized PLA nancomposites by melt blending of PLA with 20 wt% of poly(ethyleneglycol) 1000 (PEG 1000) and different amounts of MMT to investigate the thermal and morphological properties of the plasticized PLA nanocomposites. X-ray diffraction (XRD) has pointed out that all the studied MMT led to intercalated nanostructures, even the unmodified MMT had produced an intercalated structure. The researchers stressed that the particular... 

Yokohara, T. and Yamaguchi, M. (2008) Structure and properties for biomass-based polyester blends of PLA and PBS. European Polymer Journal, 44 (3), 677-685. 

The strength retention of a homogeneous blend of PLA in admixture with an additive in a certain amount can be represented as follows ... 

Blends of PLA with lauric acid, in amoimts of 2% and 5% are prepared by first dry blending the solid materials and then solution blending with 90% chloroform the materials by roller mixing. 

NatureWorlcs (2007) Technology Focus Report Blends of PLA with Other Thermoplastics, http //www. natureworkdlc.com/... 

Xu, C., Yuan, D., Fu, L., and Chen, Y. (2014) Physical blend of PLA/NR with co-continuous phase structure preparation, rheology property, mechanical properties and morphology. Polym. 

Harada et al. (2007) have prepared compatibilized blends of PLA wifli poly (butylene succinate) through addition of lysine trisisocyanate. Characterization techniques included MFR, mechanical properties, SEC, and laser scanning confocal microscopy. 

Xiao et al prepared blends of PLA with poly(butylene adipate-co-terephthalate) (PBAT), and followed their isothermal crystallization. They showed that the Avrami exponent was almost unchanged. However, the crystallization rate increased with the PBAT content. 

Blends of PLA with a dendritic hyperbranched polymer (DHP) and starch were studied by Zhang et al. They showed that addition of DHP and starch... 

Ishida et reported melt blending of PLA with four types of common rubbers, ethylene-propylene copolymer (EPM), ethylene-acrylic rubber (EAM), acrylonitrile-butadiene rubber (NBR) and isoprene rubber (IR), to toughen PLA. All blends showed separated phase morphology where the elastomer phase was homogeneously distributed in the form of small droplets in the continuous PLA phase. Izod impact testing showed that toughening was achieved only when PLA was blended with NBR, which showed the smallest rubber particle size in the blends. In addition, the interfacial tension between both phases, PLA and NBR, was the lowest. 

Blending of PLA with different thermoplastics and elastomers is an excellent alternative to copolymerization to improve PLA mechanical properties, in particular those related with the stress-strain behaviour, i.e. elastic modulus... 

Figure 14 C Is spectra of a 50 % weight blend of PLA (50 kDa) and PSA (solid line) and with electron flood gun charge compensation (crosses) (Davies et al., 1996). 

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