PLA blending

As the result, due to the poor compatibility between PLA and HA, the mechanical properties of PLA/HA composites are worse than that of PLA. Much better dispersion and homogeneity of HA in the polymer matrix can be obtained when PLA-g-AA is used in place of PLA in the composite. The PLA-g-AA/HA composites can markedly improve the mechanical properties of PLA/HA ones, and the former provides a plateau tensile strength at break when the HA content is up to 20 wt%. Furthermore, the PLA-g-AA/HA is more easily processed than PLA/HA because the former has lower viscosity than the latter as they are molten as shown in Fig. 4.15 and Fig. 4.16. Biodegradation tests of blends are also made under the en2ymatic environment, and the result shows that the mass of blends reduces by about the HA content within 4 weeks. SEM micrographs of PLA/HA (10 wt%) are shown in Fig. 4.17. 

The tendency for PLA plasticized with PEG to lose properties with time at ambient temperature is a major obstacle to its application as a biodegradable packaging material. Without plasticizer, PLA is stiff and brittle. Blending with low molecular weight PEG improves elongation at break and softness. The desired mechanical properties are achieved in quenched PLA/PEG blends with 30 wt% PEG However, the blends are not stable at ambient temperature and the attractive mechanical properties are lost over time. Crystallization and phase separation are possible aging processes. 

Crystallization and aging of slowly cooled PLA/PEG blends have been studied. Although the blend constituents are crystallizable, the blends can be quenched from the melt to the homogeneous amorphous glass. Alternatively, the blends can also be crystallized by slowly cooling from the melt. The degree of crystallization 

Attempts to improve the mechanical properties have focused on biocompatible plasticizers. Blending with PEG, the conventional name for low molecular weight ( 20 000) PEG, improves elongation at break and softness of PLA. At ambient temperature, the desired mechanical properties are achieved by blending PLA with 30 wt% PEG Table 4.2 shows the effect of PEG content on the thermal and mechanical properties of quenched PLA/PEG blends. However, there is evidence that the blend is not stable and the attractive mechanical properties are lost over time. The dynamic mechanical relaxation behavior and tensile stress-strain behavior of PLA and PLA/PEG blends are shown in Figs. 4.19 and Fig. 4.20 respectively. 

Composition PLAl/PEG Tg from DSC ( ) TgfiomE CC) 2% secant modulus (MPa) Yield stress(MPa) Fracture strain(%) 

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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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