PLA Blends

A lowering in PLA modulus and Tg can be avoided if PLA is blended with other polymers. However, it is not miscible with many plastics, and the use of block copolymers or the use of reactive blending is generally necessary. Candidate polymers may be biodegradable or nonbiodegradable. In the former category are starch. 

TABLE 12 Diffusion, Solubility, and Permeability Coefficients of Ethyl Acetate, Acetaldehyde, and 2 -Hexenal in PLA and PET Sheets 

The blending of two or more polymers is performed with the objective of achieving certain physical, rheological, or chemical properties as required for some processing or 

The moisture sensitivity of starch can be reduced by blending the polymer with hydrophobic PLA. Ke and Sun [97] characterized blends of starch and PLA in the presence of various water contents and found that the initial moisture content of the starch had a significant effect on the water absorption of the blends. The water absorption increased slowly with increasing starch content up to 60%, but 

PERMEjIOTON, sorption, and diffusion in POLY(LACnC ACID) 

TABLE 12.9 Effect of the Addition of CDs and ICs (Containing 2 -Hexenal) on PLA Permeability to Water Vapor, CO2, and O2 

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The two commercially most important Ecoflex /biopolymer blends will be presented Sects. 4.2.1. and 4.2.2. These are Ecoflex /starch blends (not marketed by BASF) and Ecoflex /PLA blends (marketed by BASF, Ecovio ). 

Eigure 6 shows the stiffness of Ecoflex /PLA blends depending on the PLA amount. PLA today is a thermoplastic polymer made from renewable raw materials and is available on industrial scale. Blending the completely different thermoplastic polyesters - stiff and brittle PLA with soft and flexible Ecoflex - a whole range of different material properties can be accessed, depending on the ratio of both polymers. 

BASE sells compostable and bio-based Ecoflex /PLA blends under the trade name Ecovio . Years of experience with biodegradable plastics and the vast compounding know-how of BASE has led to Ecovio , with most optimal mechanical properties and processability that by far exceed the properties of pure dryblends of the compound partners. 

Similar to Wu and Liao (75), Wu et al. (74) used a DMA (Model -242C, NETZSCH Co.) and a rheometer (HAAKE RS600, Thermo Electron Co.) to evaluate the viscoelastic behavior of the carboxylic-acid-functionalized MWCNTs reinforced PCL/PLA blend. Using DMA, it was observed that, with the increase of MWCNT loading, the Tg of the blend system shifted to higher temperatures. This agrees with the results obtained from the other studies discussed above and indicates the MWCNTs are compatible with the blend. The viscoelastic properties observed via rheometer were similar to those by Wu et al. (73), discussed above. 

Kenawy et al. studied the potential of electrospun fiber mats as drug delivery system for the release of tetracycline hydrochloride (Kenawy et al. 2002). Electrospun PEVA + PLA blended fibers were 1—3 pm in diameter while the PLA fibers were around 3-6 pm. Srinivasan and Reneker 1995 examined the crystal structure and morphology of the electrospun Kevlar fibers (Srinivasan and Reneker 1995). Fibers from 40 nm to a few hundreds of nanometers were produced. 

In order to monitor the changes in chain orientation as a consequence of the mechanical treatmenf the v(C=0) absorption bands of the PHB/PLA blend films were evaluated to calculate the orientation function (assuming a perpendicular transition moment of the v(C=0) absorption bands relative to the polymer chain direction) by ... 

One of the most promising applications of polyolefin hybrids is a compatibilizer for blend polymer for polyolefin and non-polyolefin. In Figure 7, TEM micrographs of PP/PMMA and EBR/poly(lactic acid) (PLA) blend polymers with and without polyolefin hybrids as a compatibilizer are displayed. Figure 7(a) represents the phase stracture of a PP/PMMA (62/38 wt%) blend polymer. Since PP and PMMA are immiscible, huge PMMA domains (> 20 pm) exist in the PP matrix. When 5 wt% of PP-g-PMMA (PMMA contents 38 wt%) was added to this blend polymer as a compatibilizer, PMMA domains were finely dispersed as is shown in Figure 7(b). As a result, the physical properties for both FM and FS were drastically enhanced from 35.3 MPa for FS and 1800 MPa for FM to 61.4 MPa for FS and 2200 MPa for FM, respectively. 

Huneault and Li described compatible blends of TPS-PLA made by free-radical grafting of maleic anhydride (MA) on the PLA backbone and then by reacting the modified PLA with the starch macromolecules in a twin-screw extruder provided with a degassing zone to eliminate water and free unreacted MA at both the PLA grafting and TPS-PLA blending steps. MA-grafted PLA showed a much finer dispersed phase, in the 1- 3 pm range, and exhibited a dramatic improvement in mechanical properties [69]. 

In addition, we prepared the set of films on the base of PLA with same thickness 40 pm and MW = 67 (defined as PLA 70), MW = 150 and 400 kDa. Along with them, we obtained the blend PHB/PLA with weight ratio 1 1 and MW = 950 kDa for PHB, and MW = 67 kDa for PLA (defined as PHB + PLA blend). Both components mixed and dissolved in common solvent, chloroform, and then cast conventionally on die glass plate. All films were thoroughly vacuum processed for removing of solvent at 40°C. 

Figure 9.24 Wavelength dependence of orientation birefringence for CAP and CAP/PLA blends stretched at a draw ratio of 2.0 PLA (circles), 1 wt% of PLA (diamonds), 3 wt% of PLA (triangles), andS wt% of PLA (squares). Reproduced with permission from M. Yamaguchi, S. Lee, M. E. A. Manaf, M. Tsuji, and T. Yokohara, Eur. Polyrn. ., 2010,46,12, 2269. 2010, Elsevier [8],...

The detailed thermal behaviours of the starch/PLA blends have been studied by DSC [204]. The experimental data was evaluated using the well-known Avrami kinetic model. Starch effectively increased the crystallization rate of PLA, even at a 1 % content, but the effect was less than that of talc. The crystallization rate of PLA increased slightly as the starch content in the blend was increased from 1 to 40 %. An additional crystallization of PLA was observed, and it affected the melting point and degree of crystalhnity of PLA. 

Abstract Biopolymers are expected to be an alternative for conventional plastics due to the limited resources and soaring petroleum price which will restrict the use of petroleum based plastics in the near future. PLA has attracted the attention of polymer scientist recently as a potential biopolymer to substitute the conventional petroleum based plastics. The chapter aims to highlight on the recent developments in preparation and characterization of PLA blends (biodegradable and non-biodegradable blends), PLA composites (natural fiber and mineral fillers) and PLA nanocomposites (PLA/montmorillonite, PLA/carbon nanotubes and PLA/cellulose nano whiskers). 

There are generally two classes of polymer blends containing PLA blends with other degradable/renewable resource polymers and blends with non-degradable polymers. A large portion of the studies on polymer blends with PLA have been on completely degradable/renewable resource blends. 

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