PVA/PHB

For a crystalline/crystalline blend, Yoshie et al. [151] studied blends of PVA and poly(3-hydroxybutyrate) (PHB). They found that PVA/PHB is compatible only when the blend contains a larger amount of PVA, and Model C was found with amorphous and crystalline PHB. Kwak et al. [94] studied poly(ether-ester)/PVC to find a common Ti, but double-exponential Tip decays. Model B was proposed with a mixed amorphous phase and two microcrystalline phases for component polymers. Note that Guo [95] reexamined this blend and pointed out that these assignments have to be reconsidered. 

Figure 9.6 SEM micrographs of biocompati- PLA in the blend 20wt%, (b) PCL of 20 wt%, ble biodegradable polyesters after their melt (c) PHB after melt spinning from a PVA/PHB blending with PVA with extrusion, cold draw- blend 90/10 by wt%, and (d) the same at ing, and extraction with water, (a) Amount of higher magnification.

Figure 17.20. SEM micrographs of microfibrillar and/or nanoporous scaffolds of (a) PHB filament spun on commercial equipment as PVA/PHB blend (80/20 by wt) and washed with water for removal of PVA, (b) PHB spun as PVA/PHB (90/10 by wt) blend and washed with water for removal of PVA, (c) PCL prepared in a similar way, and (d) PGA extruded as PP/PGA (80/20 by wt) blend and extracted with boiling xylene for removal of PP...

It was shown that the decreasing of strength of films occurs at concentration PHB greater than 10% (for LDPE-PHB mixtures) and greater than 20% (for PVA-PHB mixtures). 

The loaded concentration of PVA PHB ingredients varied as 100 0, 90 10, 80 20, 70 30, 50 50, and 0 100. The blends were produced using a single-screw extruder, ARP-20 with L/D = 25, diameter = 0.20 cm. Electricity heating was used to obtain 180°C flat extrusion profile. The components were first premixed in Brabender Plasticorder PCE330 at 170°C and at 60 rpm rotor speed, after drying the ingredients in an air oven at 101°C for 8 h. The screw rotation was 100 rpm. The films obtained with final thickness 60 mm were allowed to air cool to room temperature. 

FIGURE 7.1 Dependence of ultimate tensile on the blend compositions for films of PVA/ PHB and LDPE/PHB, respectively. 

In the initial interval (0-20% PHB) of PVA/PHB blends the stable tensile strength is shown in Figure 7.1. After 20% concentration, this parameter sharply decreased due to transition from compatible to incompatible system. The incompatible matrices are characterized by imperfection of crystalline organization. 

FIGURE 7.4 The quantity of water (g), diffused through PVA/PHB blend films. 

In spite of the crystallinity decrease in PVA, the total water diffusion is decreased also due to interaction of hydroxyl groups with carbonyl groups of PHB, and hence due to water solubility depression. For both PE/PHB and PVA/PHB blends the specific inflection points are shown. The initial stage of permeability reveals the relaxation of elements of blend structure on the molecular and crystalline levels. 

FIGURE 7.5 Dependence glass temperatures from concentration of PHB in PVA/PHB blended films. 

Fig. 6.8 SEM micrographs of biocompatible biodegradable polyesters after their melt blending with PVA with extrusion, cold drawing and extraction with water, a PIA in amount of the blend 20 wt%, b PCL of 20 wt%, c PHB after melt spinning Irom a PVA/PHB blend 90/10 by wt, and d the same at higher magnification. Reproduced with permission Irom Ref. [80] Copyright 2015 Taylor Francis...

Each of the pure polymers, P(3HB), a-PVA, and s-PVA, shows only one Ti value, indicating that the crystalline and amorphous domains of these pure polymers are smaller than is the scale of effective spin diffusion. Figure 21.14 shows the variation of the Ti values with the blend composition [120]. In the blends, the Ti values of PHB and PVA approach each other with increasing... 

In the present contribution an investigation on the biodegradation of blends and graft copolymers of PHB of both natural and synthetic origin and PVA/PVAc blends is reported. The evaluation of the effects of each component in blends and copolymers on both the overall extent of biodegradation and the biodegradation of counterparts, was investigated in aqueous media and in soil by means of respirometric tests. 

Thick films (0.5 mm) were obtained by hot pressing at 180 °C and 1.5 tons for 1 min of powdered mixtures of PVA based blends with microbial PHB and PVAc containing low molecular weight polyols. 

Three different films obtained by a hot pressing procedure of powder mixtures containing plasticized PVA, PVAc with and without bactmal PHB were submitted to the biological degradation of soil microorganisms in a respirometric test aimed at simulating soil burial conditions. The compositions of the blend films are summarized in Table 1. 

A preliminary investigation on the biodegradation of graft copolymer and blends of PVA with chemically synthesized atactic PHB was carried out in an aqueous medium by using a PVA-degrading selected bacterial culture as inoculum. 

Figure 5. Biodegradation curves of atactic PHB and PVA samples and their graft copolymers and blends in an aqueous medium in the presence of PVA-degrading microorganisms.

The limited bioassimilation observed in the case of the aPHB2 sample can be explained by considering that very likely PVA-degrading microorganisms are able to use only the low molecular weight finctions of atactic PHB. 

A biodegradation study was carried out on ternary blend systems represented by PVA containing 12% residual acetyl units, PHB of both natural and synthetic origin, and PVAc. Two basic issues were tentatively approached. In the first instance, the influence of hydrophobization of PVA-based materials, obtained by addition of bacterial PHB and PVAc, on their biodegradation in soil environment was investigated. It was ascertained that the biodegradation of PVA in soil is very limited, most likely due to the... 

Another basic issue to be considered was represented by the influence of PHB on the biodegradability of PVA in the presence of specific PVA-degrading microorganims, by considering that biodegradation of the polyester and of the polyhydroxylated polymer is strictly mediated by PHB-depolymerase and PVA-oxidase specific enzymes, respectively. In this connection, the biodegradability of both a graft copolymer and a cast blend was ascertained in the presence of a select bacterial culture able to utilize PVA. 

Blends or composites were also prepared especially by Hirano in the same way as mentioned previously for chitin [63], Other systems were proposed in the literature and listed previously [1, 2], Some of them are described in detail, for example, chitosan/ polyamide 6 and chitosan/polyamide 66 [119,120], chitosan/cellulose using a common solvent [121,122], chitosan/poly(oxyethylene) (POE) [123], chitosan/polyvinylpyrrolidone (PVP), chitosan/polyvinyl alcohol (PVA) [123,124], chitosan/polycaprolactone [124-126], chitosan/ collagen [127], chitosan/PHB [128], and chitosan/cellulose fibres [129]. In some case, the polymers are crosslinked in the blends [130]. Hydrogels or films have been prepared by mixing chitosan solution with monomers, initiator and cross-linker followed by copolymerization [131,132]. 

PHA blends with poly(vinyl alcohol) (PVA) are interesting materials whose miscibility depends on the composition and the PVA tacticity [178]. PHB is claimed to be miscible with polyethylene glycol [179] and with poly D-lactide [180] its miscibility with polyethylene oxide depends on the blend composition [181]. Immiscible, but well-compatible blends of PHB, were prepared with poly(butylene succinate-co-butylene adipate) and poly(butylene succinate-co-caprolactone) [182]. 

The same approach was applied to other biodegradable polymers as poly(beta-hydroxy-buthyric acid) (PHB), poly(caprolacton) (PCL), and poly(glycolic acid). In the last case, because of the high melting temperature of PGA at which PVA decomposes, the second blend component was PP and as a solvent for its removal xylene was used. The morphology of the scaffold materials of these polymers is demonstrated in Figure 17.20. 

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... 

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