Polylactide-Based Nanocomposites

The introduction of a few percent of nanofUlers, such as layered aluminosilicate clays, has been extensively considered to enhance PLA properties. However, the greatest improvement is usually achieved when nanoparticles are fully and uniformly delaminated (exfoliated) in the polymer matrix, a challenge that cannot be fully met by direct melt blending of the clay as this usually leads to intercalated nanocomposites [43, 44]. The use of in-situ polymerization techniques appears fully justified since the monomer can penetrate and then polymerize inside the clay sheets, enhancing the delamination efficiency. 

The molar ratio between hydroxyl groups and aluminum cations was crucial in promoting a controlled polymerization. Thus, a defect of aluminum cations should lead to more efficient aluminum triaUcoxides, but this was not the case when polymerizations were performed from lactide rings [46]. It was claimed that the probability to form a large amount of triaUcoxide species from the anchored hydroxyl groups was rather low, and most probably a mixture of aluminum mono-. 

The grafted chains pushed the lamellar sheets apart from each other and led to the achievement of an excellent degree of clay exfoliation, which, for example, leads to improved thermal stability compared to unfilled PLA and even intercalated counterparts. Moreover, while the Tg and T of the PLA matrix were not influenced by the nanofiller, the degree of crystallinity of the polyester in the exfoliated stmc-ture was significantly higher than in the intercalated nanocomposite [45]. 

Dubois et al. [46] also used in-situ polymerization to prepare a PLA-MMT mas-terbatch and confirmed that its dilution with the neat PLA during melt processing was an effective technique for improving clay dispersion. 

It is well known that brittleness is a strong Hmitation for the appHcation of PLA. 

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Goffin AL, Raquez JM, Duquesne E, Siqueira G, Habibi Y, Dufresne A, Dubois P. From interfacial ring-opening polymerization to melt processing of cellulose nano-whisker-filled polylactide-based nanocomposites. Biomacromolecules 2011 12 2456-2465. 

Raquez, J.-M., Habibi, Y, Murariu, M., and Dubois, P. (2013) Polylactide (PLA)-based nanocomposites. Prog. Polym. 

Lee SY, Xu YX, Hanna MA (2007) Tapioca starch-poly (lactic acid)-based nanocomposite foams as affected by type of nanoclay. Int Polym Process 22(5) 429-435 Lee B-H, Kim H-S, Lee S, Kim H-J, Dorgan JR (2009) Bio-composites of kenaf fibers in polylactide role of improved interfacial adhesion in the carding process. Compos Sci Technol 69 2573-2579... 

Even though this technique has been mostly used with water-soluble polymers, such as PEO, polyvinyl ether (PVE), polyvinylpyrrolidone (PVP), and poly(acrylic acid) (PAA) [134-141], intercalation from nonaqueous solutions has also been reported [142-145]. For example, high-density polyethylene (HDPE)-based nanocomposites have been prepared by dissolving HDPE in a mixture of xylene and benzonitrile with dispersed organomodified layered silicates (OMLSs). The nanocomposite was then recovered by precipitation from tetrahydrofuran (THE) [143], Polystyrene (PS)/OMLS-exfoliated nanocomposites have also been prepared by the solution intercalation technique, by mixing pure PS and organophilic clay with adsorbed cetyl pyrid-ium chloride [146]. Similarly, several studies have focused on the preparation of polylactide (PLA)-layered silicate nanocomposites using intercalation from solution. 

Fig. 1.9 (A) Exfoliation of clay platelets (white Cloisite25A and Cloisite30B after (B) two and a arrows) in a commercial polylactide matrix using half months hydrolysis and (C) after five and a a masterbatch process. (B, C) Visual aspect half months hydrolysis. (A) adapted from [144] of unfilled PLA, microcomposite based on reproduced by permission ofWiley-VCH, and CloisiteNa+, and nanocomposites based on (B, C) from [147] with permission from Elsevier.

Figure 11.29. Crystallization enthalpy of polylactide plasticized with variable amounts of polypropylene glycol having molecular weight of 1000. [Data from Paul M-A Alexandre M Degee P Pluta M Gleski A Dubois P, New Nanocomposite Materials Based on Plasticized Poly(l-lactide) and Organo-modified Montmorillonites, Belgian Polymer Group Meeting 2002, Mens, Belgium.]...

Lee KY, Bharadia P, Blaker JJ, Bismarck A (2012c) Short sisal fibre reinforced bacterial cellulose polylactide nanocomposites using hairy sisal fibres as reinforcement. Compos A 43 2065-2074 Lei Y, Wu Q (2010) Wood plastic composites based on microfibrillar blends of high density polyethylene/poly(ethylene terephthalate). Bioresour Technol 101 3665-3671 Liu D, Zhong T, Chang PR, Li K, Wu Q (2010) Starch composites reinforced by bamboo cellulosic crystals. Bioresour Technol 101 2529-2536 Liu H, Xie F, Yu L, Chen L, Li L (2009) Thermal processing of starch-based polymers. Prog Polym Sci 34 1348-1368... 

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Maiti P, Yamada K, Okamoto M, Ueda K, Okamoto K (2002), New polylactide/ layered silicate Nanocomposites role of organoclay , Chem Mater, 14, 4654-61. Paul M-A, Alexandre M, Degee P, Henrist C, Rulmont A, Dubois P (2003), New nanocomposite materials based on plasticized poly(L-lactide) and organo-modified montmorillonites thermal and morphological study . Polymer, 44, 443-50. 

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