Abstract
Graft copolymers of natural rubber (NR) and poly-3-hydroxybutyrate (PHB) with 60:40 ratio were synthesized in chlorobenzene. Two types of initiators namely azoisobutyronitrile (AIBN) and benzoyl peroxide (BPO) AIBN and BPO were employed to initiate the free radical grafting of the two polymers. The influence of the various types of initiator loadings was also investigated. Estimation of the grafted NR was performed using FTIR. The thermal stability and crystallization behavior of NR-g-PHB was studied using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) TGA as well as DSC respectively. The absence of the C=C peak of NR in the FTIR spectra confirmed that PHB grafted on this site after the breakage of the C=C bond. The increase in initiator loading, improved the smoothness of the NR-g-PHB. Moreover, single Tg were observed for NR-g-PHB which indicate that no phase separation occurs and the thermal stability of pristine NR after grafting was improved compared with that of NR alone.
Highlights
The development of materials based on renewable resources is currently being considered as one of the most promising ways for overcoming the environmental concerns related to major synthetic polymers
When AIBN initiator was employed, the Natural rubber (NR)-g-PHB copolymer formed a lot of small separated pieces on the glass mold as compared to the benzoyl peroxide (BPO) initiator, which gave a smoother surface as shown in Figure 1 (a-b)
The breakages in the NR-g-PHB membrane could be due to the insufficient occurrence of grafting and/or crosslinking between NR and PHB, which can be proven by the rapid dissolution of the grafted polymer in chloroform solvent
Summary
The development of materials based on renewable resources is currently being considered as one of the most promising ways for overcoming the environmental concerns related to major synthetic polymers. While PHB has shown excellent properties for certain applications, it is a very brittle plastic and prone to thermal degradation at temperatures above the melting point [6]. Other works reported the grafting of PHB onto cellulose via reactive extrusion using dicumyl peroxide as radical initiator [6]. Most previous works on PHB grafting used high temperatures around 175 -180 oC for the grafting reaction [6, 15, 16]. As a result of the use of this high temperature, thermal degradation of PHB occurred almost exclusively by random chain-scission. Afterwards, the NR-g-PHB was kept in the oven for 2 days at a certain casting temperature to maximize the grafting and cross-linking reactions. These steps were repeated with another initiator (BPO) allowing working at slightly higher temperature
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