Aging studies of a polypropylene and natural rubber blend

International Journal of Industrial Chemistry pp 1–8 | Cite as Aging studies of a polypropylene and natural rubber blend AuthorsAuthors and affiliations Chaouki BendjaouahdouSalima Bensaad Open Access Research First Online: 11 December 2018 73 Downloads Abstract The literature relatively lacks results and data related to the direct influence of physical aging on the properties of polypropylene and natural rubber blend; so, the objective of this research was to study the influence of thermal and ultraviolet (UV) aging on a natural rubber (NR) SMR-ω and polypropylene (PP) blend. This toughened blend is generally used for the fabrication of automobile parts and in the construction industry. The loading of the NR was 10, 20, 30, 40 and 50 wt%. The blends were prepared by calendering followed by melt extrusion and it was subjected to XRD (WAXS) analysis, mechanical testing, thermal and UV aging, and optical microscopy (OM) observations. The results obtained by X-ray characterisation show that the adding of this kind of rubber does not affect the crystalline structure of the polypropylene matrix. Moreover, the adding of the rubber shows a decrease of the obtained material tensile strength and a valuable increase of the elongation at break. The shore A hardness decreases slightly as the percentage of the natural rubber increases. The optical microscopy indicates the apparition of cracks at the sample surfaces and debonded rubber domains from polypropylene matrix induced by UV and thermal aging. KeywordsAging Rubber Mechanical properties Blend X-ray  Introduction The mixing of various kinds of polymers is a suitable method for the development of blends with characteristics better to those of the individual components. Properties of a polymeric blend or mixture depend mainly on the matrix phase (major component) but factors like amount, shape, size, and interfacial adhesion of the discontinue phase (minor component) also are important [1, 2, 3, 4]. The resulted binary blend of polypropylene (PP) and rubber component is called a thermoplastic elastomer (TPE). Thermoplastic elastomeric materials (TPEs) can be obtained from a blend of PP and various natural or synthetic types of rubbers. This kind of blend has the characteristics combination of thermoplastic and elastomeric phases [5, 6, 7, 8, 9, 10, 11, 12] and it can be treated like thermoplastic materials. The majority of TPEs have non-uniform morphology. The TPEs based on rubber and thermoplastic compositions have been synthesized along two different procedures. One consists of a simple blend and the resulted mixture is called a thermoplastic elastomeric olefin (TPO). In the second procedure, the elastomeric phase is dynamically vulcanized, leading to a thermoplastic vulcanizates (TPVs) or also called dynamic vulcanizates (DVs). The TPVs are characterized by finely dispersed micron-sized cross-linked elastomeric particles distributed in a thermoplastic matrix [13]. The dynamic vulcanization operation makes the morphology of the material more stable. Consequently, a uniform and finer distribution of rubber particles in the thermoplastic matrix is obtained [14]. TPV procedure is based on the crosslinking of a rubber with cross-linking agents (sulfur or organic peroxide) to form a discontinuous phase of cured rubber, distributed in a continuous matrix of a thermoplastic [15]. The extensively used thermoplastic component is polypropylene (PP). PP has various applications due to its unique properties such as high melting temperature, low density, high chemical solvents and heat resistances. Furthermore, PP exhibits poor impact strength, which limits its applications. Different rubbers were blended with PP to prepare TPEs such as ethylene–propylene–diene rubber (EPDM), nitrile rubber (NBR), ethylene–propylene rubber (EPR), and rubber waste from truck and car tires [16, 17, 18, 19, 20, 21]. The aim of this research is to study the influence of UV and thermal aging on the mechanical properties of polypropylene and natural rubber blend. In this study, SMR-ω natural rubber (SMR) was blended with PP to produce a polypropylene and natural rubber binary blend. The loading of the elastomeric component (SMR) in the blend was 10, 20, 30, 40 and 50 wt%. The PP/SMR blends were subjected to mechanical testing carried out before and after thermal and ultraviolet (UV) aging and these blends were also subject to optical microscopy (OM) observations. Experimental Materials A commercially and not stabilized isotactic polypropylene (trademarked as X 34-981903308, produced by APPRYL SNC, France) with Mw/Mn = 4, a melting temperature of 169 °C, an isotacticity index of 98% and a melt flow index (MFI) of 0.148 g/min (measured at 190 °C under a 2.16 kg load) was used as the major blend component. The natural rubber (SMR-ω grade) was purchased from the Malaysian Rubber Board (MRB). The main characteristics of natural rubber type SMR-ω are: 0.92 g/cm3 (specific gravity); Nitrogen (max. 0.60 wt%); volatile matter (max. 0.80 wt%): plasticity retention index (min. 30%); Mooney viscosity, ML, 1 + 4 (100 °C) 130. The natural rubber was used as received. The twin-roll mill had a nip clearance equal to 0.5 mm and a friction ratio of 1.3 (20/15 rpm), and the blending was carried out for 15 min. We began by mixing polypropylene (PP) pellets on the two-roll mill for 10 min; afterwards, little lumps of natural rubber (SMR) were added during 10 min. Finally, the resulted mixture was extruded in an extruder having a single screw. Preparation of the samples Before blending, polypropylene and grinded SMR natural rubber (SMR) were dried in an oven at 80 °C for 24 h. The components were melt-blended at 175 °C in a two-roll mill (BRABENDER POLYMIX 200P). The extruder used was a SCHWABENTHAN PLE 330 apparatus; it had a length/diameter ratio of 21, a diameter of 20 mm, a thread thickness of 5.4 mm, and a step between two consecutive threads of 15 mm. The barrel temperature (from feed zone to die) and screw speed were set, respectively, at 170–180–190 °C and 45 rpm. The screw used was conventional. Five formulations were studied, so that the weight ratio PP/NR was 90/10, 80/20, 70/30, 60/40 and 50/50. Characterizations X-ray diffraction analyses (XRD) were done on an Xpert Philips diffractometer interfaced with a computer and operating at 40 kV and 40 mA in a continuous mode. The incident ray had a wavelength of 1.54 Å generated by a CuKα anode. The 2Θ range was 1.51–19.98° with a scanning rate of 0.028°/min. The composite specimen analyzed by X-ray diffraction was films of 0.5-mm thickness that were obtained by compression and heating at 175 °C. Tensile characterization was done at ambient temperature (23 ± 2 °C) according to ASTM D 417 with a ZWICK ROELL Z100 testing machine interfaced with a computer. The specimens having a dumbbell shape extended at 100 mm/min crosshead speed. The reported values of the tensile properties represent averages (...truncated)