# Effect of LNR-g-MMA on the Mechanical Properties and Lifetime Estimation of PLA/PP Blends
## 2 Experimental
### Preparation of LNR-g-MMA  
A total of 227 g of the NR latex, having a 60% DRC (dry rubber content), was mixed with Emulvin WA (C\({}_{24}\)H\({}_{22}\)O\({}_{2}\)), used as a surfactant, and distilled water in a flask equipped with a condenser and stirrer. The NR latex was acidified by formic acid to pH = 5, followed by successive treatment with 0.3 mol of H\({}_{2}\)O\({}_{2}\) and 0.02 mol of NaNO\({}_{2}\) at 65 \({}^{\circ}\)C for 12 h. Following the reaction, 5% sodium sulfite solution was added to the mixture to remove excess H\({}_{2}\)O\({}_{2}\). Then, the latex was left for 24 h at room temperature to obtain LNR with M\({}_{\text{n}}\) = 17,139 g/mol.  
Scheme 1 shows oxidative degradation in producing hydroxyl\(-\)terminated LNR. Free radicals formed from the bond cleavage will lead to the degradation of NR [31].  
The graft copolymerization was then continued by adding 2.26 mol of MMA. The LNR seed latex was swollen with the monomer mixture for 24 h at room temperature before adding the redox initiation system, consisting of 0.02 mol of cumene hydroperoxide and 0.02 mol of tetraethylene pentamine. The polymerization reaction was performed at a stirring speed of 400 rpm for the desired time of 8 h at 70 \({}^{\circ}\)C. The polymerization was stopped by adding phenol. The post\(-\)treatment included the coagulation of polymer latex and washing with deionized water. The gross polymer was recovered and dried to a constant mass in a vacuum oven at 40 \({}^{\circ}\)C.  
The proposed mechanism of preparing LNR\(-\)g\(-\)MMA initiated with cumene hydroperoxide and tetraethylene pentamine is shown in Scheme 2. The cumyloxyl [32], dimethylphenyl carbinol, or hydroxyl [33] radicals (generated from cumene hydroperoxide) tend to favor the abstraction of \(\alpha-\)methylenic hydrogen from the allylic carbon in the polyisoprene backbone, leading to the formation of polyisoprene radicals that initiate MMA to form the graft copolymers.  
Ungrafted LNR was washed out for 24 h in a soxhlet extractor using 60-80 \({}^{\circ}\)C boiling point petroleum ether. The residue was dried to a constant weight in an oven at 40 \({}^{\circ}\)C under vacuum for 24 h. The residue was extracted in acetone to remove the free polymer. The weight of the initial sample and extracted samples were measured for the determination of the graft copolymer and free polymer contents. In this system, the grafting efficiency (GE) was calculated using the following relationship:  
\[\text{Grafting efficiency }(\text{GE, }\%)=\frac{\text{total weight of MMA grafted}}{\text{total weight of MMA polymerize d}}\times 100 \tag{1}\]  
After solvent extraction, FTIR analysis was performed on the graft copolymer. Figure 1 depicts the FTIR spectrum of the residue (the graft copolymer). At wavenumbers 837, 1729, and 3400 cm\({}^{-1}\), three peaks are attributable to the R\({}_{2}\)C=CHR bending of isoprene and C=O stretching of ester groups of MMA, and the stretching mode of the hydroxyl groups, respectively. This demonstrates that the graft copolymer was formed during the grafting of MMA onto LNR.  
Using SEM, the morphology of the particles was investigated. The grafting of MMA onto LNR is an emulsion copolymerization of core-shell type. The gloomy domain is LNR, and the bright domain is PMMA. The surface of the LNR is smooth, as shown in Figure 2a. A rough layer on the surface grafted onto the surface of the LNR particles is present. The LNR\(-\)g\(-\)MMA particles (86% GE) were composed of the LNR core (gloomy domain) and the compatibilized PMMA shell (bright domain), which was able to completely cover the gloomy spheres (Figure 2b). Figures 1 and 2 provide evidence of MMA grafting on the LNR backbone chain in the core-shell latex particles.