Rubber Phase Research Articles

Interfacial molecular dynamics of styrenic block copolymer-based nanocomposites with controlled spatial distribution

The dielectric properties of nanocomposites of polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) triblock copolymers containing organically modified clay nanoparticles featuring controlled spatial orientation at the nanoscale: isotropic, totally oriented and partially oriented, have been investigated and correlated with the nanocomposite morphologies. A slow dielectric relaxation process attributed to elastomer chains with reduced mobility confined at nanoparticle/polymer interphase was observed in all the nanocomposites and was found to be dependent on the orientation of nanoclay and polystyrene (PS) domains, the location of clay tactoids as well as the PS block fraction. A dielectric “interfacial” glass transition temperature Tgi assigned to this characteristic relaxation was estimated to occur at temperatures ranging between 6 °C and 35 °C depending on the nanocomposite, which is much higher than the bulk rubber phase glass transition temperature, normally lower than −40 °C for the studied block copolymers. Interestingly, the highest Tgi were associated with the nanocomposites featuring random or partial orientation and/or selective location of nanoparticles in the rubber phase.

A new approach to fabricate polypropylene alloy with excellent low-temperature toughness and balanced toughness-rigidity through unmatched thermal expansion coefficients between components

A new strategy for fabricating polypropylene alloy with good low-temperature toughness was reported. Glass transition temperature (Tg) of rubber phase in polypropylene/ethylene-propylene rubber/poly(styrene-b-ethylene/propylene) diblock copolymer (PP/EPR/SEP) blend was continuously reduced through strengthening the interfacial tensile force on rubber phase by using the concept of mismatched thermal expansion coefficient. As a result, the brittle-tough transition (BTT) of PP alloy shifted to lower temperature and subsequently excellent impact strength at low temperature was achieved. Through qualitative analysis of impact force, it was found that the theoretical temperature at which BTT occurred was close to that obtained by experiment, indicating BTT of rubber toughened plastic system is indeed controlled by rubber's Tg at impact instant. Furthermore, the PP alloy with excellent low-temperature toughness shows balanced toughness-rigidity, on the contrary, the blends presents poor rigidity when SEP or EPR is used to toughen PP alone.

Physical and Mechanical Properties of ENR Compatibilized NR/NBR Blends Reinforced Nanoclay and Nanosilica

SummaryProperties of the unfilled rubber blends (Natural rubber, NR and Nitrile Butadiene Rubber, NBR) were poor due to the absence of reinforcing agent. However, the strength of compound had been improved with the addition of nanofiller. There were two (2) types of nanofillers that had been introduced which are nanoclay (NC) and nanosilica (NS). NR/NBR composites were prepared by open milling process where different amount of nanofiller was added ranging from 1 until 7 phr. There are a few possibilities might occur when using small particles size of fillers especially in term of interaction between rubber‐filler and filler‐filler interaction. Apart from that, different polarity and composition of both rubbers were influenced the interaction between filler and rubber phases. The interaction between non‐polar and polar rubber was enhanced using epoxidized natural rubber (ENR). The rubber compound was cured via a conventional sulphur vulcanization system. The cure characteristic result shows that the incorporation of nanofiller does not affect much on the t90. The physical and mechanical properties of epoxidized natural rubber (ENR) compatibilized NSi‐NR/NBR blends were determined by conducting the density measurements, hardness and tensile tests. The NC filler gave the highest tensile strength compared to NS. On top of that, reduction trend on the tensile strength observed at 3 phr of NS loading due to the formation of NS aggregates. The values of moduli, hardness and densities of vulcanizates increased as the nanofiller loading increased. It occurs due to better filler dispersion in the rubber matrix and strong interaction between filler‐rubber phases. The result shows that NC has more pronounce effect on the physical and mechanical proportion of the rubber vulcanizates.

Nanocomposites of NR/SBR Blend Prepared by Latex Casting Method: Effects of Nano-TiO2 and Polystyrene-Encapsulated Nano-TiO2 on the Cure Characteristics, Physical Properties, and Morphology

Nanocomposites of 80/20 (w/w) natural rubber (NR)/styrene butadiene rubber (SBR) blend with four loadings of either nanosized titanium dioxide (nTiO2) or polystyrene-encapsulated nTiO2 (PS-nTiO2), ranging from 3 to 9 parts by weight per hundred of rubber (phr), were prepared by latex casting method. The PS-nTiO2 synthesized via in situ differential microemulsion polymerization displayed a core-shell morphology (nTiO2 core and PS shell) with an average diameter of 42 nm. The cure characteristics (scorch time, cure time, and cure rate index), mechanical properties (tensile properties, tear strength, and hardness), thermal stability, glass transition temperature, and morphology of the prepared nanocomposites were quantified and compared. The results showed that the cure characteristics of all the nanocomposites were not significantly changed compared to those of the neat NR/SBR blend. The inclusion of an appropriate amount of either nTiO2 or PS-nTiO2 into the NR/SBR blend apparently improved the tensile strength, modulus at 300% strain, tear strength, hardness, and thermal stability but deteriorated the elongation at break of the nanocomposites. Based on differential scanning calorimetry, the glass transition temperature of all the nanocomposites was similar to that of the neat NR/SBR blend. Moreover, the morphology of the PS-nTiO2-filled rubber nanocomposites fractured surface analyzed by scanning electron microscopy showed an improvement in the interfacial adhesion between the rubber phase and the nanoparticles.

Silver rubber-hydrogel nanocomposite as pH-sensitive prepared by gamma radiation: Part I

Silver rubber-hydrogel nanocomposite based on silver/styrene butadiene rubber/polyvinylpyrrolidone/methacrylic acid (SBR/PVP/MAA)/Ag was prepared by gamma radiation-induced crosslinking. During the radiation crosslinking of SBR/PVP/MAA solution containing silver nitrate AgNO3 (0.01 mol), in situ reduction of Ag+ ions was performed under the radiolysis of water. The properties of sliver rubber-hydrogel nanocomposite were investigated by FT-IR, XRD, TEM, SEM, DSC and TGA techniques. Transmission electron microscope (TEM) reveals that AgNPs have uniform distribution and spherical shape with mean diameter in the range of 8–10 nm. Differential scanning calorimetry (DSC) results of the nanocomposite showed one phase suggesting the miscibility between rubber and hydrogel phases. The swelling measurement of the synthesized silver rubber-hydrogel nanocomposite in different pHs at room temperature was performed. The results showed that it has pH-sensitivity.

Rotational mobility of the radical probe in butadiene-nitrile rubbers

The difference in co-monomer composition of the disordered phase of butadiene-nitrile rubbers of BNKS and SKN grades is determined by EPR spectroscopy. The degree of aggregation of fragments consisting of alternating units and looseness of the disordered rubber phase in the case of BNKSs are shown to be higher than those of SKNs. The rotational mobility of the radical-probe indicates the lowering of the straight chain flexibility to be more pronounced in the case of BNKS rubbers. This phenomenon is due to the more large-size nanostructures if compared to the ones in SKNs.

Morphological explanation of high tear resistance of EPDM/NR rubber blends.

The fatigue properties of cross-linked blends of ethylene propylene diene rubber (EPDM) with low natural rubber (NR) content and reinforced with carbon black (CB) are studied. It is found that such EPDM/NR compounds have superior crack growth resistance and fatigue lifetime. For low NR contents, transmission electron microscopy reveals that the NR phase forms small droplets of 20-50 nm. Remarkably, these droplets are even smaller than the primary CB particles. Atomic force microscopy shows that the the NR phase droplets have a higher loss factor and a smaller elastic modulus than the surrounding EPDM matrix. Rheometer measurements are used to study the effect of the phase morphology on the rubber mechanical properties. These rheological data are compared with the prediction of the Eshelby model describing the effect of elastic inclusions on solids. A complex interplay between the rubber phase morphology and the solubility of both the sulfur cross-linking system and CB is observed, which cannot be predicted theoretically. It is proposed that the soft NR droplets effectively inhibit the crack propagation in the EPDM matrix.

Property improvements of natural rubber and low density polyethylene blends through dynamic vulcanization

Polymer blends are prepared by melt mixing, solution or latex blending. Thermoplastic vulcanizates (TPVs) are generally produced by melt mixing. TPVs can be co-injected or co-extruded to produce complex articles built from very soft/hard components. Dynamic vulcanization would give rise to a uniform and fine distribution of rubber and thermoplastic phases. The aim of this study was to identify a suitable dynamic vulcanization system to produce natural rubber (NR)/low-density polyethylene (LDPE) blends with improved chemical, ageing and morphological properties. Three 50:50 NR/LDPE blends were prepared by varying the vulcanizing agent as sulphur, dicumyl peroxide (DCP) and 50:50 sulphur: DCP. A control was prepared without any vulcanizing agent. All these blends were prepared by melt mixing. The blends were characterized using FTIR spectroscopy and SEM analysis of tensile fracture surfaces. Water absorption, swelling and ageing behaviour of the blends were investigated. Water absorption percentage of blends prepared with DCP and the mixed curing system was zero. Analysis of gel content indicated a higher crosslink density for the blend prepared with the mixed curing system compared to the other blends. Also, the former blend showed the highest retention of strength properties and elongation at break compared to the other two blends prepared with vulcanizing agents. SEM analysis showed a fine and smooth textured morphology for this blend. Results in overall indicated that the 50:50 NR/LDPE blend prepared with the mixed curing system would be suitable to manufacture heat and solvent resistant products.

Early growth of rubber in the Dry Zone of Sri Lanka: an investigation in Vavuniya District

In view of supporting the rubber product manufacturing sector in Sri Lanka and providing stable income for the peasant community, rubber cultivation is in the process of expanding to the drier regions of the country. Under this programme, rubber was introduced to the Northern region (Dry Zone) in 2010 with a tentative set of agronomic protocols. The present study showed that rubber cultivated in this region under smallholder conditions together with irrigated short term crops, has shown reasonable growth with an average annual girth expansion rate of 8.6cm. A growth curve for the immature phase of rubber was established for the first time for the dry zone of Sri Lanka. Despite some adverse effects of dry weather on photosynthesis and associated physiological parameters, no evidence of permanent damages to photosynthetic apparatus was recorded. Further actions to be taken in the expansion process of rubber cultivation in this region are also discussed.

Raman investigation of thermoplastic vulcanizates based on hydrogenated natural rubber/polypropylene blends

Raman spectroscopy including mapping technique appears as a powerful technique for the characterization of polymer blends like thermoplastic elastomers (TPEs) and thermoplastic vulcanizates (TPVs). The Raman spectra of polymers blends such as natural rubber/polypropylene (NR/PP) and 65% hydrogenated natural rubber/polypropylene (65%HNR/PP) were identified and the phase distribution was determined. The study was driven for the same type of blends in TPEs state and TPVs state obtained after to 2 different processes, either peroxide cure or sulfur cure. The morphology of TPEs and TPVs obtained by Raman spectroscopy were compared and confirmed using scanning electronic microscopy.Raman mapping shows that the phase morphology of NR/PP, 65%HNR/PP, were characterized as continuous rubber phase morphology of the thermoplastic elastomers (TPEs) and a fine dispersion of cross-linked rubber phase in a continuous matrix of the thermoplastic vulcanizates (TPVs). Raman spectroscopy is demonstrated to be a reference to determine the content ratio of each component in the TPVs. Moreover, Raman mapping could be used to calculate the phase size of cross-linked rubber phase dispersed in the thermoplastic vulcanizates (TPVs).

In situ polarity functionalization and properties of styrenic triblock copolymers synthesized via RAFT emulsion polymerization

ABSTRACTThe in situ polarity functionalization of the styrenic triblock copolymers was accomplished via the block introduction of polar monomer, n‐butyl acrylate, with the help of reversible addition‐fragmentation chain transfer (RAFT) emulsion polymerization. The polarity functionalization, microphase separation, static and dynamic mechanical properties, water resistance, transparency, and thermal stability of the synthesized polarity‐functionalized triblock copolymers, polystyrene‐block‐poly(n‐butyl acrylate)‐block‐polystyrene (SAS), were extensively studied. The poly(n‐butyl acrylate) (PBA) middle block higher than 10 wt % has the favorable toughening effect on polystyrene (PSt) two‐end block due to the microphase separation in SAS. The glass transition of the continuous plastic phase (mainly composed of PSt block) has a much greater influence on the storage modulus than that of the dispersed rubber phase (mainly composed of PBA block). The polarity‐functionalized SAS has good water resistance, high transparency, and robust thermal stability. The polarity‐functionalized SAS will have such a potential application broadening as polar adhesive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44603.

Cure and scorch in the processing of ethylene‐propylene‐diene terpolymer (EPDM)

ABSTRACTThe objective of this work is to ascertain the characteristics of desirable (cure) and especially undesirable (scorch) crosslinking when carbon black filled ethylene propylene diene terpolymer (EPDM) is processed using different peroxide initiators. The mixing temperature and the nature of the peroxide initiator are crucial parameters affecting scorch (undesirably premature crosslinking) in this rubber. Processability and properties of EPDM prepared using various mixer set temperatures have been investigated. Dicumyl peroxide (Luperox DC), di(t‐butylperoxy) diisopropylbenzene (Luperox F), and 2,5‐dimethyl‐2,5‐di(t‐butylperoxy) hexane (Luperox 101) were used as crosslinking initiators. Higher mixing temperatures give shorter scorch times, greater scorch magnitudes, greater heterogeneities in crosslink spatial distribution and poorer tensile properties. However, extreme localization of the unwanted crosslinking at the rubber‐filler interface does have a beneficial effect. Luperox DC offers poorer processability and poorer resulting properties than do Luperox F and Luperox 101, due to its shorter half‐life and greater solubility in the rubber phase. This is the first time that the spatial heterogeneity of crosslinking and scorch has been related to the basic thermodynamics of 3‐component 2‐phase systems. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44523.

Natural rubber grafted poly(methyl methacrylate) as compatibilizer in 50/50 natural rubber/nitrile rubber blend

The effects of graft copolymers applied as compatibilizers for natural rubber/nitrile rubber (NR/NBR) blends at 50/50 (w/w) on cure characteristics, mechanical properties, thermal properties, oil resistance, and morphology were investigated. The graft copolymers of methyl methacrylate (MMA) onto NR initiated by benzoyl peroxide (NR- g-PMMA<BPO>) and by potassium persulfate (NR- g-PMMA<PPS>) under emulsion polymerization were synthesized and used to compatibilize the blends. The structures of the copolymers were characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. NR was blended with NBR via a two-roll mill at 70°C under the compatibilizer loading ranging from 0 to 10 parts per hundred of rubber (phr). The results showed that the tensile property and tear strength of the blends increased with the increasing amount of NR- g-PMMA<BPO> as a compatibilizer. Thermal aging determined in terms of tensile properties exhibited the smaller difference between before and after aging in an oven with the increasing compatibilizer loading. The morphology of the compatibilized NR/NBR vulcanizates was investigated by scanning electron microscopy of the tensile fracture surfaces, which exhibited the improvement of interfacial adhesion between the two rubber phases. The thermal properties of compatibilized NR/NBR vulcanizates were reported in terms of a glass transition temperature under differential scanning calorimetry and dynamic mechanical analysis. The incorporation of an appropriate amount of the compatibilizer into the blends apparently improved the oil resistance of NR. Among them, the blend filled with 7.5 phr of NR- g-PMMA<BPO> showed the lowest volume change in IRM 903 oil.

Thermoplastic Vulcanizate Based on Poly(lactic acid) and Acrylic Rubber Blended with Ethylene Ionomer

ABSTRACTA new thermoplastic vulcanizate (TPV) was developed by meltblending of poly(lactic acid) (PLA), acrylic rubber (ACM), and ethylene-methacrylic acid with sodium ions (EMAA-Na). The PLA/ACM/EMAA-Na blend showed low-yield strength, low modulus, and excellent strain recovery. It also demonstrated an increase in complex viscosity and decrease in melting temperature due to the interfacial reaction between the PLA and the ACM phases. The Fourier transform infrared spectroscopy results indicate that EMAA-Na can interact with both PLA and ACM, and that the Na+ ions act as a catalyst for the interfacial reaction between PLA and ACM, while PLA does not react with ACM without EMAA-Na. Moreover, the tensile strength at break of the PLA/ACM/EMAA-Na blend was observed to be extremely improved by the addition of hexamethylenediaminecarbamate (HMDC) due to the increasing of the cross-link density inside the rubber phase. The morphology of the PLA/ACM/EMAA-Na blend with HMDC was finer than that of PLA/ACM/EMAA-Na without HMDC. From the results, it is suggested that the interfacial reaction between the PLA and the ACM phases, the cross-linking in the ACM phase, and the finer morphology improved the mechanical properties of the blend.

Effect of core-shell particles dispersed morphology on the toughening behavior of PBT/PC blends

Methyl methacrylate-co-styrene-co-glycidyl methacrylate grafted polybutadiene (PB-g-MSG) and styrene-co-glycidyl methacrylate grafted polybutadiene (PB-g-SG) core-shell particles were prepared to toughen poly (butylene terephthalate) (PBT) and polycarbonate (PC) blends. The compatibilization reaction between the epoxy groups of glycidyl methacrylate and the carboxyl groups of PBT induced the PB-g-SG particles dispersed in the PBT phase. On the other hand, the good miscibility between PMMA (the shell phase of PB-g-MSG) and PC induced the PB-g-MSG particles dispersed in the PC phase. The different phase morphology led to different toughening behavior. The PBT/PC/PB-g-MSG blends with the PC encapsulated morphology showed much lower brittle-ductile transition core-shell particles content (10-15 wt% or 15-20 wt%) compared with the PBT/PC/PB-g-SG blends (20-25 wt%). The difference between the toughening efficiency of the core-shell particles was due to the change of deformation mechanisms. In PBT/PC/PB-g-MSG blends, the cavitation of PB rubber phase led to the occurrence of shear yielding of the matrix. While in the PBT/PC/PB-g-SG blends, the debonding between PBT and PC interface induced the shear yielding of the matrix. The variation of the core-shell particles dispersed phase morphology also affected the crystallization properties and DMA results of the PBT/PC blends. Modification of the phase morphology provided an useful strategy to prepare PBT/PC blends with higher toughening efficiency.

Mechanical and Thermal Properties of Toughened PLA Composite Foams with Modified Coconut Fiber

Composite foams from PLA, natural rubber and modified coconut fibers was prepared employing a compression molding method, which is suitable for the fabrication of composites containing high fiber content. The results revealed that the incorporation of natural rubber into composite foams increases the compressive stress to 101.17 kN/m2. Further, a 10% wt increase of modified coconut fiber added into composite foams resulted in an increase of compressive stress to 105.24 kN/m2. The addition of modified coconut fibers in composite foams showed a slight decrease of the crystallization state, obtained by DSC results by about 1-3 oC. Thus, modified coconut fibers played a role as a nucleating agent. Moreover, the combination of modified coconut fibers in composite foams could lead to improved adhesion between the surface area of PLA matrix and the natural rubber phase.

Effect of entanglements in the microstructure of cured NR/SBR blends prepared by solution and mixing in a two-roll mill

The influence of preparation methodology of vulcanized elastomeric blends of natural rubber (NR) and styrene butadiene rubber (SBR) on the phase morphology and network structure has been studied. Two different compounding methodologies have been applied: (i) mechanical mixing in a two-roll mill and (ii) blending in solution, by dissolving the elastomers in an appropriated solvent.Samples with different NR/SBR ratios were vulcanized by using a conventional cure system based on sulfur and TBBS (n-t-butyl-2-benzothiazole sulfenamide) as accelerator. The phase distribution of rubber matrices in the blends was investigated by transmission electron microscopy (TEM), identifying differences in the compounds according to the preparation method.Weak residual dipolar couplings caused by the existence of cross-links and topological constraints in vulcanized samples were characterized by using proton multiple-quantum (MQ) NMR spectroscopy. The structural results obtained by NMR and equilibrium swelling experiments were compared and complemented with viscosity measurements.It was found that the preparation method has a strong influence on the phase morphology of blends and the molecular network structure of each rubber phase, with an important variation in the entanglements contribution, which is more pronounced when the prepared blends are richer in NR.

Bio-based Blends of Wheat Gluten and Maleated Natural Rubber: Morphology, Mechanical Properties and Water Absorption

Wheat gluten (WG) is a complex protein derived from wheat. WG-based plastics are potentially used as substitutes for conventional petroleum-based plastics. However, the WG plastics are brittle and have high moisture absorption after being processed. In order to reduce stiffness and increase water resistance of the WG plastics, in this work, maleated natural rubber (NRMA) was blended with the WG. Grafting MA on the natural rubber (NR) is able to increase polarity of the NR, thereby increasing compatibility between the WG and NR. The NRMA was prepared by grafting maleic anhydride (MA) on natural rubber (NR) in molten state in an internal mixer at 120°C with no initiator for grafting reaction. Under the grafting condition used in this work, it was found that the grafted MA content on the NR is about 1.78% determined by alkaline titration. Sulfur as a curing agent in the rubber phase was used to prepare WG/NRMA blends with various weight ratios (100/0, 90/10, 80/20, 70/30, 60/40 and 50/50). Mechanical properties, impact strength, water absorption and morphologies of the molded WG/NRMA blends compared with WG/NR blends were investigated. Incorporation of the NRMA into WG improved flexibility and water absorption resistance of the polymer blends with respect to the neat WG. Moreover, the WG/NRMA blends provided higher impact strength and mechanical properties, especially modulus and tensile strength than those of WG/NR, indicating more compatibility between the WG and NRMA comparing to NR, resulting in an improvement of mechanical properties in the WG/NRMA blends.

Poly1‐hexene: New impact modifier in HIPS technology

ABSTRACTPoly1‐hexene was prepared using a conventional heterogeneous Ziegler–Natta catalyst and its stereoregularity was characterized using 13C‐NMR analysis. New kind of high impact polystyrene (HIPS) was prepared by radical polymerization of styrene in the presence of different amounts of synthesized poly1‐hexene (PH) as impact modifier (HIPS/PH) and compared with conventional high impact polystyrene with polybutadiene (HIPS/PB) as rubber phase. Scanning electron microscopy (SEM) revealed that the dispersion of poly1‐hexene in polystyrene matrix was more uniform compared with it in HIPS/PB. The impact strength of HIPS/PH was 29–79% and 80–289% higher than that in HIPS/PB and neat polystyrene, respectively. FTIR was used to confirm more durability of HIPS/PH samples toward ozonation. To study the effect of rubber type and amount on the Tgs of polystyrene, differential scanning calorimetry was employed. Results obtained from TGA demonstrated higher thermal stability of HIPS/PH sample in comparison with conventional HIPS/PB one. Our obtained results suggest new high impact polystyrene that in all studied aspects has better performance than the conventional HIPS. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43882.

Correlation of viscosity ratio, morphology, and mechanical properties of polyamide 12/natural rubber blends via reactive compatibilization

Natural rubber (NR)-modified polyamide 12 (Nylon12/NR) was produced by melt blending Nylon12 and NR in the presence of polystyrene/maleated natural rubber (PS/MNR) copolymer as a reactive compatibilizer. The influence of compatibilizer loading on viscosity ratio, morphology, and mechanical properties of the blends was investigated. As a consequence of the reactive blend between Nylon12 and maleated NR in PS/MNR, the formation of amide and succinimide linkages was set at rubber-Nylon12 interfaces. Thus the dispersion of rubber particles was improved, and the particle coalescence was prevented so that the fine morphology with good interfacial adhesion was stabilized. This also resulted to enhance the blend viscosity and to lower viscosity ratio. The data revealed strong correlation between low viscosity ratio and fine spherical morphology of the compatibilized blends. An optimum PS/MNR compatibilizer content was at 7 phr to produce good dispersion of small rubber domains (size ≤0.3 μm) in Nylon12 matrix. Thermal properties by DSC revealed that crystallization temperature of Nylon12 was lowered by the presence of NR and crystallinity of Nylon12 was slightly affected by the PS/MNR content. An enhancement of mechanical properties, especially the impact energy was observed without suffering the tensile and flexural properties. Compared to the neat Nylon12, the compatibilized blends showed an increase in impact energy by a factor of 5. This large enhancement is successfully interpreted in term of the toughening effect by rubber phase of suitable dispersed size and the interparticle distance.