Vol.:(0123456789) 1 3 Iran Polym J DOI 10.1007/s13726-017-0547-8 ORIGINAL PAPER Improvements in morphology, mechanical and thermal properties of flms produced by reactive blending of poly(lactic acid)/natural rubber latex with dicumyl peroxide Chutimar Deetuam 1  · Chavakorn Samthong 1  · Parichat Pratumpol 1  · Anongnat Somwangthanaroj 1   Received: 10 December 2016 / Accepted: 10 July 2017 © Iran Polymer and Petrochemical Institute 2017 molecules. According to our study, it can be summarized that to optimize the morphology, mechanical properties, and gas permeation property of the free radical-assisted reactive blends, it is of great concern to carefully balance reactive compatibilizer formation and gel formation by adjusting the DCP content. Keywords Poly(lactic acid) · Natural rubber · Reactive blend · Dicumyl peroxide · Mechanical properties Introduction Over recent years, biodegradable biopolymers have gained much interest as eco-friendly materials in replacement of conventional petrochemical-based plastics because they are produced by fermentation/polymerization of the renewable agricultural sources (sugarcane, tapioca, corn, etc.) and can decompose into carbon dioxide, water, and biomass in a short time as a result of enzymatic action of microorgan- isms [1]. Among them, poly(lactic acid) (PLA) is a com- mercially available aliphatic semicrystalline polyester with many promising properties including high optical appear- ance, high tensile strength, biodegradability, and biocompat- ibility [2–4]. Therefore, PLA has been continuously used for diverse applications such as green food packaging [5, 6] and in the tissue engineering feld [7, 8]. Unfortunately, neat PLA shows brittle fracture behavior (elongation at break less than 4% [2]); this could restrict its applications. Numerous methods have been conducted to toughen PLA. Manipulation of the content of stereoisomers and degree of crystallinity in the PLA structure can alter the mechanical properties and biodegradability of PLA; however, tough- ened PLA using this technique still has poor properties, which is not enough for some advanced applications [9, Abstract The efect of dicumyl peroxide (DCP) as a free- radical cross-linking agent on the morphology, thermal and mechanical properties, and gas permeation of blown flms prepared by reactive blending of poly(lactic acid) (PLA) and natural rubber latex was investigated. In comparison to the blown flms without DCP, SEM micrographs revealed that the amount of debonded rubber domains from the cryof- ractured surface reduced considerably. This was when DCP at 0.003 phr was incorporated and the free radicals from thermally decomposed DCP reacted with PLA and NR chains, generating PLA–NR copolymers and cross-linked NR as confrmed by FTIR spectra. These PLA–NR copoly- mers acted as compatibilizers, which increased the strength at the PLA/NR interfaces, leading to the improvement in tensile strength, elongation at break, tensile toughness, impact strength, and tear strength. Although DCP did not infuence the cold crystallization of PLA, TGA thermograms showed that thermal stability slightly increased owing to the enhanced interfacial adhesion. However, the addition of DCP at 0.005 and 0.010 phr resulted in a high content of cross-linked NR gel, by consuming the free radicals instead in copolymer formation. Therefore, the compatibilization efciency was signifcantly reduced and the mechanical properties of reactive PLA/NR blown flms fnally dropped. Also, this poor interfacial adhesion facilitated the micro- void formation at the polymer–rubber interface as a result of mechanical stretching upon the flm blowing process, increasing the permeation of water vapor and oxygen * Anongnat Somwangthanaroj Anongnat.S@chula.ac.th 1 Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand