Plasticization of PLA

Citrate plasticizers are nontoxic and approved for many food packaging and medical applications. Based on the 

FIGURE 16.17 Stress-strain plots for neat PLA, PLA/PPG4, PLA/PPGl, and PLA/PEG blends. Plasticizer content indicated in the figure. Reprint from Ref. 273. Copyright 2006, with permission of Elsevier. 

TABLE 16.4 Hansen Solubility Parameters of PLA and Other Normal Plasticizers [276] 

FIGURE 16.18 Cross sections of the PLA/PEG 70/30 blend as viewed in the polarizing light microscope after aging at ambient conditions for different periods of time. Reprint from Ref. 213. Copyright 2003, with permission of Elsevier. 

PLA values were determined according to the Hansen solubility parameters method with 18 solvents and R value = 5.6. The distance for the plasticizer was calculated according to distance = [4(i5d8 — (5dp) + 

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Epoxidized oils were also used to modify PLA Ali et ah (2009) reported that its use as a plasticizer to improve flexibility. Thermal and scanning electron microscope analysis revealed that epoxidized soybean oil is partially miscible with PLA. Rheological and mechanical properties of PLA/epoxidized soybean oil blends were studied by Xu and Qu (2009) Epoxidized soybean oil exhibited a positive effect on both the elongation at break and melt rheology. Al-Mulla et al. (2010b) also reported that plasticization of PLA (epoxidized palm oil) was carried out via solution casting process using chloroform as a solvent. The results indicated that improved flexibility could be achieved by incorporation of epoxidized palm oil. 

Even though the addition of plasticizers for plasticization of PLA will overcome the brittleness but, it comes with a sacrifice of stiffness of the material which... 

Figure 2 Two cycle test at a maximum fixed load for the determination of the elasticity and plasticity of PLA yams Straining at the maximum load SI, Immediate Elastic Recovery lER, Delayed Recovery DR and Permanent Set PS. The trigger load was 5% of Qmax.

This chapter treats the external plasticizing of PLA, while Chapter 4 Reactive extrusion discusses internal plasticizers. This chapter seeks to give an overview of recent results in order to provide the reader with some simple guidelines to successfully plasticizing PLA with external plasticizers. 

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-... 

To improve the properties of PLA, plasticizers, special additives such as chain-extenders, polymer blends, and composites are commonly investigated. Martin and Averous (10) have studied the effects of various plasticizers on the properties of PLA. Pilla et al. (11-12) have investigated the effects of chain-extenders on the foaming properties of PLA. In addition, a vast number of studies have been conducted to enhance the properties of PLA by blending it with various polymers such as polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinyl acetate, polyolefins, polystyrene, HIPS (high impact polystyrene), polyacetals, polycarbonate, and acrylonitrile butadiene styrene (ABS) (13-26). 

PLA compares well with petrochemical-based plastics used for packaging. It is clear and naturally glossy like polystyrene, it is resistant to moisture and grease, it has flavour and odour barrier characteristics similar to polyethylene terephthalate (PET). The tensile strength and modulus of elasticity of PLA is also comparable to PET. 

In 2004, Office Media (Tokyo) developed a new PLA film exhibiting vastly improved functionality as a packaging material. Through combination with other biodegradable plastics, the film s transparency, flexibility, heat resistance and impact resistance, have been balanced in multiple dimensions, and through adopting two-layer and three-layer structures, gas barrier properties have also been improved. Technology to eliminate the characteristic odour of PLA developed independently by Office Media, have also been applied. 

For rigid thermoformed packaging, the stiffness of PLA enables more efficient down gauging versus existing PET materials. PLA is also an alternative to traditional plastic films such as cellophane, cellulose acetate and glassine, as well as a low temperature heat seal layer and/or flavour and aroma barrier in co-extruded structures where its combination of properties allows layer simplification or replacement of specific layers. 

PLA is finding new applications in speciality cards such as credit, membership, retail and gift cards. Biodegradable polymers provide retailers and brand owners with an opportunity to provide a more responsible environmental position to traditional plastics such as PVC for these applications. The rigid properties of PLA sheet allow it to be easily scored and PLA also exhibits an optimum surface for printing and varnishing. 

In November 2005, BASF announced that it was expanding its Ecoflex-brand natural plastic line with Ecovio, a blend of NatureWorks PLA and Ecoflex, which is polyester-based. Ecovio production began in October 2005 at an undisclosed location in Germany. The first Ecovio LBX 8145 grade contains 45% by weight of PLA that is chemically bound to the Ecoflex. BASF said the first application will be in flexible films used for shopping bags. 

In 2005, UK mineral water brand Belu launched the UK s first biodegradable mineral water bottle made of PLA. The company chose biodegradable plastics as a means of enhancing its environmental credentials. The new bottle is available through outlets that already stock the brand, including the Waitrose retail chain, London restaurants and clubs such as Nobu, Sketch and the Groucho Club. 

PLA may be fabricated into film for packaging and is also made into fibers useful for carpeting (24). PLA is indeed biodegradable, but only under controlled composting conditions. Biodegradation of poly (lactic acid) requires temperatures of about 140 °F for many days to insure decomposition, ultimately into CO and water. Unfortunately, such conditions are not typical of landfills (3) or of most backyard compost heaps. Hence, even plastic bags made from PLA will not quickly disappear from the natural environment. Anaerobic decomposition of PLA results in liberation of methane, an even more potent greenhouse gas than CO (25-28). 

The Tg of bulk ethylcellulose is in the range of 129-133 C, and therefore at ambient conditions films of ethylcellulose are substantially brittle. To be used in film coating applications, ethylcellulose requires the addition of pla.sticizer to improve film flexibility and toughness. The Tg of dried latex particles of Aquacoat ECD has been reported to be 89 C (7). The reduced Tg of ethylcellulose particles dried from a pseudolatex is the result of the temporary plasticizing effects of water. Although the Tg of ethylcellulose... 

For perfectly plastic materials, post>yieldtng the strain rate is a constant function of the stress and the stress is constant and never exceeds ay (Fig. ISA). The extent of pla.stic deformation p depends upon the proportionality between plastic strain rate and the stress and the how long the. stress is applied as shown in Figure 17A. The elastic perfectly plastic material is highly idealized and not many materials exhibit this type of behavior. 

KAUFMAN, M., The First Century of Pla.stics, The Plastics Institute, London (1963)... 

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