PLA-based Materials

Inc., and Teijin Ltd., which is known as Ingeo in the USA and Biofront in Japan. Another company, Purac, also produces biomedical application-oriented PLA-based materials under the PURASORB brand name. Figure 8.1 shows the synthesis, recycUng, and degradation of PLLA [13]. However, due to the recent initiation of the production of biobased polyethylene (PE) from bio-ethanol, PLLA is not the sole mass-produced biobased polymer. To forestall biobased PE and other biobased polymers that will be produced in the near future, high performance PLA-based materials must be developed to suppress their hydrolytic/thermal degradabiUty and increase their mechanical performance. 

Porous PLA-based materials can be used as scaffolds for the regeneration of organs. These materials are prepared by the formation of a phase-separated structure of PLA-based materials... 

Electrospinning of PLA and copolymers [12] and the PLA stereocomplex [145,146] has been used to prepare nanofibres or nanomats. Similar to the effect of pores on the mechanical properties of PLA-based materials, the formation of nanomats effectively lowers the E and elevates the 8b value. The morphology of the fibres and nanomats and the mechanical properties are affected by the applied voltage, the effluent rate and concentration of the solution, the type of solvent and so on (Figure 8.12 [147]). 

The hydrolytic degradation of PLAs and copolymers has been intensively studied, and, as a result, there are more than 250 papers related to this issue [188,189]. The degradation mechanism, behaviour, and rate depend on material- and media-related factors, which are summarized in Table 8.3. In addition, the methods used to monitor the hydrolytic degradation of biodegradable polymers are summarized in Table 8.4. Detailed information regarding the hydrolytic degradation of PLA-based materials can be found in the related review articles [188-190],... 

Polymer blending is commercially advantageous to prepare PLA-based materials with a wide variety of physical and hydrolytic degradation properties. There are five primary factors... 

As stated above, the hydrolytic degradation resistance of PLA-based materials was enhanced by stereocomplex formation. However, even in the molten state (i.e. above the I m of the stereocomplex crystallites), the PLLA/PDLA blend has a higher thermal resistance than neat PLLA or PDLA [275,276]. 

Table 8.9 Fillers of PLA-based materials for biomedical applications. ...

Fibrous fillers of PLA-based materials for industrial and biomedical applications are summarized in Tables 8.8 and 8.9, respectively [182-184, 382-416]. Nonbiobased fibres that are used for the preparation of fibre-reinforced PLA-based plastics are multiwall carbon... 

Since the early 2000s, plant-derived biobased fibrous fillers have been frequently used for the reinforcement of PLA-based materials. A well known and frequently used plant-derived fibrous filler is kenaf. Like the case of pollen as an additive, the wettability between PLLA and kenaf should be improved by the addition of a compatibilizer. Other fibrous materials are cellulose fibrous materials or fibres [383,384], cellulose whiskers [385], recycled cellulose fibre [386], cotton fibre [387], sugar beet pulp [388], flax [389], bamboo fibre [390], kenaf [391-393], papyrus [394], hemp fibre [395], cuphea and lesquerella [396], ramie [397], rice straw fibre [398], red algae fibre [399], miscanthus fibre [400], abaca fibre [401], milkweed [402], wood fibre [403] and recycled newspaper fibre [404], Poly(L-lactic acid) fibre can also be used to reinforce soft plastics such as PCL [405],... 

Qiopped glass fibers and recycled newspaper cellulose fibers can be used to reinforce PLA base materials for their use as composites (36). The composites can be fabricated in a twin screw extruder and an injection molding device. 

At present, PLA-based materials are mainly referenced on three different markets, namely, the biomedical (initial market), the textile (mainly in Japan) and the packaging (mainly food, i.e. short-term applications). For instance, reported types of manufactured products are blow-moulded bottles, injection-moulded cups, spoons and forks, ther-moformed cups and trays, paper coatings, fibres for textile industry or sutures, films and various moulded articles [8]. 

However, the main drawback of PLA-based materials remains their high brittleness to be addressed to span PLA applications from commodity to engineer-... 

Plasticization is frequently used to improve the processing behavior and the flexibility of PLA-based materials [48]. The extent of plasticization depends on the miscibility of plasticizers with host polymers as a function of molecular weight and loading level [41], but undesirable decrease in stif iess of the as-plasticized materials, together with the undesired leaching of the plasticizers over time are often observed [41,45,47]. 

Figure 10.15 Morphologies of impact-fractured surfaces of PLA-based materials containing 10wt% (a), 20wt% (b), and 30wt% (c) of EAC. Reproduced with permission from Ref. [116] 2010, John Wiley and sons.

It is worth pointing out that the use of impact modifiers in PLA can be accompanied by some decrease of both tensile strength and modulus. Other approaches have thereby been proposed to enhance both impact and tensile properties of PLA-based materials by combining impact strengtheners with nanoparticles, the formation of interpenetrated networks and annealing process/crystallinity extend as discussed below. 

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