Blends of PHB and PLA

In polarization spectroscopy, the structural absorbance Aq is frequently calculated from the band intensities measured with radiation polarized perpendicular (AJ and parallel (A, respectively, by Equation 9.1  

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  

For a non-phase-separated blend of P H B/ P LA, the visual image of the elongated polymer appears homogeneous and has a uniform thickness [53]. This observation is also reflected in the images derived from the PHB- and PLA-specific absorption bands. Furthermore, the orientation function of the PHB and PLA absorption bands is, over the whole area, negative and positive, respectively. 

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Polymer blends of PHB and PLA have previously been analyzed with miscellaneous methods by several other groups [49-51]. In the following, the used of transmission FT-IR imaging will be demonstrated as an alternative approach towards a better understanding of the chemical and physical properties of these materials. 

One of the fields of polymer science for which FT-IR imaging has proved of extraordinary importance in terms of scientific and practical aspects is the analysis of phase separation in polymer blends. Blending of different polymers is a Ifequently used technique in industrial polymer production to optimize the material projrerties. As pointed out in Chapter 5.01, the mechanical properties of PHB can be enhanced by blending with FLA. For the preparation of the optimum blend, it has to be taken into account that the miscibility of different polymers depends on their concentration, the temperature, and their stmaural characteristics. Polymer blends of PHB and PLA have previously been analyzed with miscellaneous methods by several other researchers and in what follows the application of transmission FT-IR imaging will be demonstrated as an alternative approach toward a better tmderstanding of their chemical and physical properties. 

The FT-IR transmission spectra of the individual blend components PHB and PLA and of a PHB/PLA (50 50wt%) blend film are shown in Figure 9.21a and b, respectively. In Figure 9.21a, only a limited number of absorption bands are detectable which are specific for the individual blend components PHB and PLA. For FT-IR imaging, primarily the nonoverlapped left and right wings of the intense... 

In accordance with the discussion of Figures 9.25c and d, they reflect a sUghtly positive orientation for PHB and PLA in the matrix and an opposite orientation for the two polymer components (PHB negative, PLA positive) in the islands . These figures clearly demonstrate that the polarization spectra recorded with a single-element detector cannot discriminate between the different orientation mechanisms in the phase-separated, anisotropic structure of this polymer blend. 

Biodegradable polymer blends of polyanhydrides and polyesters have been used as drug carriers [59], Polyflactic acid) (PLA), polyfhydroxybutyrate) (PHB), and poly(caprolactone) (PCL), of 2000 and 50000 molecular weights were mixed with poly(sebacic anhydride) (PSA), and the properties of these mixtures were studied. Mixtures of PHB and low molecular weight PLA or PCL formed uniform blends with various amounts of PSA. These blends possess different physical and mechanical properties compared to the parent polymers. The release rate of drugs from these polymeric blends increases with the increase in the content of the rapidly degrading component, PSA. 

A mixture of PHBV with PLA had a positive effect on the elasticity modulus, elongation at break and flexural strength for different blends. However, tensile strength did not improve in any of them. In the same way, Zhang et al (1996) reported improved mechanical properties for blends of PHB/PLA compared with the common PHB. In addition, PVA (polyvinylacetate) grafted on PIP (poly-cis-l,4-isoprene) and mixed with PHB had... 

The three most common biobased biodegradable polymers are PLA, PHA, and TPS. PLA, PHA, and TPS can be made into plastic containers, packaging, bags, and bottles. All three biobased polymers can be processed with traditional plastics processing equipment. Polyhydrox-yalkanoates can be made from over 100 monomers based on P3HB, P4HB, PHB, and PHV. PHA is produced in the cells of several types of bacteria. Polylactide, or polylactic acid, is made from starch and bacteria. Thermoplastic starch is a blend of starch and other additives. 

It was suggested that the changes on the blends occurred where a heat treatment was applied, because of transesterification between the PHB and PLA chains. 

To provide a comparison of the spectral data obtained by FT-IR and Raman microspectroscopy, the Raman spectra of a PHB-rich and a PLA-rich domain of the same blend film (PHB/PLA 50/50 wt%) are shown in Figure 22.8. These spectra clearly demonstrate the high selectivity of the PHB and PLA band separation in the 1710-1800 cm wavenumber region corresponding to the v(C=0) vibration, and in the 800-900 cm range which has been assigned to a coupled mode of v(C—O) and v(C—C) vibrations [11]. 

Figure 8.22 PHB gjj/PLA gj ratio versus content of PLA for the PHB- and PLA-rich image areas of the different blend compositions (see text). (Reproduced with permission from Ref. [57] 2008, ACS Publications.)...

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