Polylactide crystallization

Nam, J.Y., Ray, S.S., Okamoto, M. Crystallization behavior and Morphology of biodegradable polylactide/layered silicate nanocomposite. Mactomolecules 36, 7126-7131 (2003)... 

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

Maillard D. Prud homme R. E. The crystallization of ultrathin films of polylactides Morphologies and transitions. Canadian Journal of Chemistry, vol.86, No.6, (2008), pp. 556-563. 

Nam, I.Y., Okamoto, M., Okamoto, H. et al. (2006) Morphology and crystallization kinetics in a mixture of low-molecular weight aliphatic amide and polylactide. Polymer. 47,1340-1347. 

Mechanical performance of material can also be influenced by the effect of the plasticizer on polymer crystallization. This was reported for plasticization of polylactide by fatty acid ester. This process requires not only the right combination of materials but also specific thermal conditions (in the reported study, crystalhzation was observed after exposing material to 100°C for 24 h). 

Figure 11.28. Glass transition temperature, Tg, and crystallization temperature, T, of polylactide plasticized with variable amounts of epoxidized polypropylene glycol having molecular weight of 640 daltons. [Data from McCarthy S Song X, Antec 2001.Conference proceedings, Dallas, Texas, 6th-10th May, 2001, paper 363.]...

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.]...

The properties of PLA, as indeed those of other polymers, depend on its molecular characteristics, as well as on the presence of ordered structures, such as crystalline thickness, crystallinity, spherulite size, morphology and degree of chain orientation. The physical properties of polylactide are related to the enantiomeric purity of the lactic acid stereo-copolymers. Homo-PLA is a linear macromolecule with a molecular architecture that is determined by its stereochemical composition. PLA can be produced in a totally amorphous or with up to 40 per cent crystalline. PLA resins containing more than 93 per cent of L-lactic acid are semi-crystalline, but, when it contains 50-93 per cent of it, it is entirely amorphous. Both meso- and D-lactides induce twists in the very regular PLLA architecture. Macromolecular imperfections are responsible for the decrease in both the rate and the extent of PLLA crystallization. In practise, most PLAs are made up of L-and D,L-lactide copolymers, since the reaction media often contain some meso-lactide iir turities. 

Cartier, L, Okihara, T, Ikada, Y, Tsuji, H., Puiggal, J., and Lotz, B. (2000) Epitaxial crystallization and crystalline polymorphism of polylactides. Polymer, 41, 8909-8919. 

R., and Runt, J. (2001) Crystallization and solid-state structure of random polylactide copolymers poly(L-lactide-co-D-lactide)s. Macromolecules, 34, 4857-4864. 

A.L., and Meaurio, E. (2005) Stereoselective crystallization and specific interactions in polylactides. Stere-ocomplexation and morphology of polylactides. Macromolecules, 38,... 

Crystalline structure and molecular dynamics in alpha and alpha crystals of poly(L-lactide) (PLLA) and PLLA/poly(D-lactide) (PDLA) stereocomplex crystals have been investigated by solid-state C CPMAS NMR spectroscopy. The crystal forms of polylactide (PLA) have different line shapes, and resonance splittings in solid-state NMR spectra due to the crystallographically inequivalent sites within crystal unit cell. 

Polylactides (PLAs) have two enantiomeric forms, PLLA and PDLA. It is well known that a 1 1 mixture of PLLA and PDLA can form stable stereocomplex (SC) crystals, which have... 

The PDLA, PLLA or high d- or L-lactide copolymers have regular structures. The polylactides are either amorphous or semicrystalline at room temperature, depending on the molecular weight and content of l, d or meso-lactide in the main chain. PLA can be totally amorphous or up to 40% crystalline. PLA resins containing more than 93% L-lactic acid can crystallize. However, high molecular weight can reduce the crystallization rate, and therefore the... 

Montmorillonite (MMT), a smectite clay, is probably the most extensively studied nanomaterial in terms of mechanical, thermal, fire retardant or crystallization behavior of polylactide, especially when these nanoparticles are organically modified allowing the achievement of intercalated and exfoliated nanocomposites.These nanocomposites show enhanced properties as compared to microcomposites and pristine polymer. However, biodegradation and hydrolytic degradation of PLA in the presence of nanoclays has been investigated to a small extent. 

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... 

The subject of crystallization from stressed melts has been reviewed (Kumaraswamy 2005) and one frequent occurrence in the time sequence of this crystallization is the formation of row nuclei which give rise to structures known as shish-kebabs . Polypropylene is the polymer best known for its remarkable propensity for forming row structures, which often contain considerable amounts of P-phase material (Olley et al. 2014), and are a major feature of the skin-core stmcture of injection-moulded polypropylene (Shinohara et al. 2012), but they are also found in polyethylene (An et al. 2006), isotactic polystyrene (Azzurri and Alfonso 2008), poly(phenylene sulfide) (Zhang et al. 2008) and polylactide (Xu et al. 2013). 

Maillard D, Prud homme RE (2008) Crystallization of ultrathin films of polylactides from chain chirality to lamella curvature and twisting. Macromolecnles 41 1705-1712 Mano JF, Wang Y, Viana JC, Denchev Z, Oliveira MJ (2004) Cold crystallization of PLLA studied by simultaneous SAXS and WAXS. Macromol Mater Eng 289 910-915... 

Singh NK, Singh SK, Dash D, Gonugimta P, Misra M, Maiti P (2013) CNT Induced p-phase in polylactide unique crystallization, biodegradation, and biocrunpatibility. J Phys Chem C 117 10163-10174... 

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