Processing of PLA

The physical properties and melt processing of PLA are similar to those of conventional packaging resins. It may thus be used as a commodity resin for general packaging application. In many aspects the basic properties of PLA lie between those of crystal PS and PET [ 14]. When plasticized by its own monomer lactic acid, PLA becomes increasingly flexible so that products that mimic PVC, LDPE, LLDPE, PP, and PS can be prepared [15]. Possible applications are espe-... 

Among the applications discussed in this chapter, the most prominent in recent years is CNT-reinforced polymer nanocomposites. The use of CNTs in polymers can provide superior mechanical properties (60). For instance, the addition of 1% CNTs might increase the stiffness of polymers by 10% and increase their resistance to fracture however, improvements in the properties of CNT-reinforced polymers largely depend on the dispersion of CNTs within the polymer matrix and the polymer-CNT interfacial properties. The following section highlights several studies regarding the processing of PLA-CNT nanocomposites. 

Three parts are covered in the chapter. First, the synthesis and properties of PLA are described. The modification and process of PLA are also discussed. Then, the composites with PLA as matrix and natural fiber or nanoparticles as reinforcement are reported in the second part. The processing and the properties of the composites are also given. The interface between PLA and the reinforcement and the surface treatment methods are discussed. Finally, the application and the development of PLA and PLA-based composites in the future are proposed. 

The products can also be recycled after use for second time and they can even be hydrolyzed back into lactic acid which is the basic monomer. Nevertheless, the recycled lactic acid can be re-introduced into the polymerization process of PLA. The last possibility is to introduce PLA into the natural life cycle of aU biomass where it degrades into carbon dioxide and water. Thus, the diversity of PLA becomes obvious as it can be recycled and also decomposed like all other organic matter. Besides that, it will do no harm if burned in an incineration plant or introduced into a classical waste management system (Jacobsen et al. [1]). The typical values of mechanical properties of PLA are displayed in Table 11.1. 

Atactic PLA has been prepared by polymerization of a lactide race-mate. It has an amorphous structure. Isotactic PLA has been prepared by the polymerization of D-lactide or a L-lactide and it is crystalline. Syndiotactic PLA can be obtained from cyclic dimer of lactic acid, e.g., meso-lactide (3). Production processes of PLA resins include (4) ... 

Figure 4.6 Methine H-radical abstraction and maleation process of PLA (reproduced with John Wiley and Sons permission from Ref. 84).

While these previous studies offered valuable insights, demonstrating the continuous extrusion process of PLA foamed with supercritical CO2, the morphology achieved in foamed PLA failed to satisfy the definition of microcellular foam due to lower cell population density (less than 10 cells/ cm ) with cells being larger than 60 m in average size. Distinctions between these features and microcellular foam... 

One feature that is inherent to PLA fibers is the ability to hold a crease or fold. This excellent crease retention property facilitates pleats or wrinkles processing of PLA fabrics. For instance, the unique design of PLA eco-bags (kna plus , Japan) with pleats or wrinkles allows the bags to compactly fold up for storage and has created a sensation in many shops including Smithsonian Instimtion (USA). 

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