Natural rubber–isotactic polypropylene thermoplastic blends

Abstract

Thermoplastic elastomers, prepared by melt blending of natural rubber (NR) and isotactic polypropylene (PP) through a dynamic vulcanization technique, were developed during the later 1970s. However, they have certain drawbacks due to thermal degradation and higher molecular weight of NR. In the study reported here, NR was masticated to different levels prior its addition to isotactic polypropylene to improve the flow properties and to reduce the incompatibility resulting from molecular weight mismatch of NR/PP thermoplastic blends. Mixing energy curves of uncrosslinked blends and those of dynamically vulcanized blends crosslinked using different cure systems were compared. The mixing energy curves of blends containing NR of different molecular weight (M n ) and two grades of PP (injection and film grades) were also compared. Technological and processing properties of the dynamically vulcanized (sulphur and peroxide cure systems) and unvul-canized blends were compared with those of the samples containing unmasticated NR. The results indicated that a number average molecular weight in the range 4 ϫ 10 5 for NR increased the procoessability without significantly affecting the technological properties of NR/PP thermoplastic blends. Among the three cure systems studied Luperox 101 and dicumyl peroxide gave better technological properties than the sulphur-cured samples. Two antioxidants, viz. quinoline (TDQ) and imidazole (MBI) type, were tried in NR/PP blends. It was found that TDQ imparts better aging resistance compared to MBI. The improvement in processability due to the reduction in molecular weight of natural rubber by mastication is more noticeable in the case of peroxide vulcanized blends compared to sulphur vulcanized samples.

Interrelationships of morphology, thermal and mechanical properties in uncrosslinked and dynamically crosslinked PP/EOC and PP/EPDM blends

“…When the curative is added, torque value increases, reaches maximum and then decreases before being stabilized. Typical torque-time relationship of 50/50 PP/EOC and PP/EPDM uncrosslinked and Babu et al -eXPRESS Polymer Letters Vol.4, No.4 (2010) 197-209 Decrease in torque value after reaching the maximum is expected due to the combined effect of the disintegration of crosslinked EOC or EPDM domains and also by the degradation in the PP phase through β-scission [22]. The maximum torque value after adding the curative and the torque value at the end of the mixing cycle for different compositions are given in the Table 3.…”

“…co-continuous morphology is changed into dispersed phase morphology. The less viscous PP encapsulates the more viscous crosslinked rubber particles to minimize the mixing energy [22,23]. At equal curative dosage of 2 phr DCP and compositional volume, PP/EPDM TPV shows coarser crosslinked rubber particle size than PP/EOC TPV (Figures 2c and 2d).…”

Dual phase continuity and phase inversion phenomena in natural rubber/ethylene vinyl acetate (EVA) copolymer blends

“…Various types of thermoplastics have been used to prepare TPNRs. These include polypropylene [12][13][14], polyethylene [15,16], polystyrene [17], polyamide-6 [18], and poly(methyl methacrylate) [19]. Ethylene-vinyl acetate copolymer (EVA) has also been used to prepare the TPNRs [20][21][22][23] due to its excellent ozone damage resistance, aging ability, weather resistance, and mechanical properties [24].…”

Efficiency of high energy electrons to produce polypropylene/natural rubber‐based thermoplastic elastomer

“…A thorough literature survey reveals that most of the study deals with PP/NR TPOs [3, 4] and TPVs [5, 6]. Conventional crosslinking systems, like sulfur [7–10], peroxides [9–15], and phenolic resins [16, 17] have been used abundantly in comparison to high energy electrons to produce PP/NR TPVs. The use of high energy electrons for dynamic vulcanization is quite difficult and requires a special experimental setup as well as experimental data from the electron beam treatment at room temperature.…”