Melt reaction in blends of poly(3‐hydroxybutyrate) (PHB) and epoxidized natural rubber (ENR‐50)

Abstract

Melt reaction in blends comprising immiscible biopolymer, poly(3-hydroxybutyrate) (PHB), and epoxidized natural rubber with 50 mol percent level of epoxidation (ENR-50), prepared by solvent-casting, has been studied. Differential scanning calorimetry (DSC) technique was used to measure the heat of reaction under isothermal annealing. The heat of reaction increases with respect to PHB and ENR-50 content as long as they constitute the dispersed phases and exhibits a maximum at about 50% PHB. A reaction mechanism comprising degradation of PHB chains to shorter chains bearing carboxyl end groups that subsequently react with epoxide group of the ENR-50 is proposed, providing the basis for kinetic analysis and determination of parameters that characterize the melt reaction. Two-phase morphologies, formed in the blends upon melting of PHB, transform within minutes to homogeneous phase as observed under optical polarizing microscope. The two glass transition temperatures observed at -18.4 and 1.2°C for blends are associated, respectively, with immiscible ENR-50 and PHB phases. After annealing at 190°C an inward shift was observed, gradually closing in with increasing annealing time, and eventually merging into a single transition. This is an indication of progressive change in miscibility of the blends, as an effect of the melt reaction. FTIR spectra provide further evidence that supports the ring opening reaction of the epoxide group by the carboxyl group.

Silver sulfide/poly(3-hydroxybutyrate) nanocomposites: Thermal stability and kinetic analysis of thermal degradation

“…The carboxylic terminal groups of the degraded PHB react with other compatible functionalized polymers at sufficiently high temperatures. In fact, our group has previously reported upon melt reactions in blends of PHB and a modified natural rubber, namely 50% epoxidized natural rubber, ENR-50 [17]. In this case, oxirane ring opening reactions were induced by carboxylic terminal groups of the degraded PHB upon heating the PHB/ENR-50 blend to slightly above the melting temperature of PHB.…”

Reprocessability of PHB in extrusion: ATR-FTIR, tensile tests and thermal studies

“…Therefore, there has been a great deal of interest in studying the thermal degradation behavior of PHB and other related poly(hydroxyalkanoate)s [29][30][31][32][33][34][35] . Also studies seeking to improve the thermal stability of PHB by grafting chemicals in PHB chain [33,36] , and adding polymeric additives in PHB matrix [37,38] have been developed. The thermal degradation behavior of PHB has been discussed in many works [14,20,21,30,[39][40][41][42] , in which a random chain scission reaction (β-elimination) involving a six-membered ring transition state ( Figure 1) has been considered as the main mechanism based on typical structures of pyrolysis products, i.e., crotonic acid and oligomers with a crotonate end group, i. e., unsaturated end groups.…”

Effect of Organo-Modified Nanoclay on the Thermal and Bulk Structural Properties of Poly(3-hydroxybutyrate)-Epoxidized Natural Rubber Blends: Formation of Multi-Components Biobased Nanohybrids

“…It has been demonstrated that most of the polymer blends are immiscible and tend to separate into macroscopic phases and reveal clear individual glass transition temperatures [3,8,9,19]. Lee et al [20] reported that in blends of PHB/ENR-50, the carboxyl end group of degraded PHB and the epoxide group of ENR are reactive and may affect chemical and physical, as well as structural changes at the interfaces of the immiscible PHB and ENR phases. They also pointed out that the extent of miscibility is more pronounced in molten state.…”