B. T. Poh

Effect of filler loading on tensile and tear properties of SMR L/ENR 25 and SMR L/SBR blends cured via a semi-efficient vulcanization system

Abstract The effects of filler loading on the tensile and tear properties of SMR L/ENR 25 and SMR L/SBR blends using a semi-efficient vulcanization system was studied. Carbon black (N330), silica (Vulcasil C) and calcium carbonate were used as the fillers and the loading range was from 0 to 40 phr. Tensile strength, M300 (tensile stress at 300% elongation) and tear strength were determined using a Monsanto Tensometer (Model T10) operating at 50 cm/min. Results show that for the carbon black and silica-filled blends, elongation at break decreases, but tensile strength, M300 and tear strength increase with filler loading. The reverse behavior is obtained for the calcium carbonate-filled blends. This observation is attributed to the better rubber–filler interphase interaction of carbon black and silica compared to the non-reinforcing nature of calcium carbonate, the dilution effect of which becomes more significant as the filler loading is increased. For a fixed filler loading, SMR L/ENR 25 blend consistently exhibits higher tensile strength, M300 and tear strength but lower elongation at break compared to SMR L/SBR blend. This finding is associated with the mutual rubber reinforcement between the two strain-induced crystallizable rubbers (i.e. SMR L and ENR 25), coupled with good rubber–filler interaction, particularly between silica and ENR 25 in the former blend.

Cure characteristics of unaccelerated sulfur vulcanization of epoxidized natural rubber

The curing characteristics of unaccelerated sulfur vulcanization of ENR 25 and ENR 50 were studied in the temperature range from 100-180°C. The range of sulfur loading was from 1.5 to 6.5 phr. The scorch time was determined by Mooney Shearing Disk Viscometer whereas the initial cure rate, maximum torque, and reversion properties were obtained from the Moving Die Rheometer (MDR 2000). Results shows that ENR 25 gives a longer scorch time than ENR 50, an observation similar to that in an accelerated system reported earlier. For temperature < 120°C, scorch time depends exponentially on sulfur loading for both rubbers. However, this dependence diminishes as temperature is increased. This observation is attributed to the availability of activated sulfur molecules for vulcanization. The initial cure rate and maximum torque increases with increasing sulfur loading. ENR 50, however, exhibits higher value than ENR 25, suggesting faster cure in the former. For a fixed sulfur loading, reversion is a time and temperature-dependent phenomenon. It decreases with increasing sulfur loading because of the increase of cross-linking density for both rubbers studied.

Effect of blend ratio on Mooney scorch time of rubber blends

The Mooney scorch times of three rubber blends [epoxidized natural rubber (ENR) 50/SMR L, ENR 50/styrene butadiene rubber (SBR), and Standard Malaysian Rubber SMR L/SBR] were studied in the temperature range of 120-160°C using an automatic Mooney viscometer. N-Cyclohexyl-2-benzothiazyl sulfenamide was used as the accelerator, and the rubber formulation was based on the conventional vulcanization system. Results for the blends investigated indicate that a negative deviation of scorch time from the interpolated value was observed, especially for temperatures lower than 130°C. This observation was attributed to the induction effect of the ENR 50 in the ENR 50/SMR L and ENR 50/SBR blends to produce more activated precursors to crosslinks, thus enhancing interphase crosslinking. To a lesser extent, SMR L also exhibited such an induction effect in the SMR L/SBR blend. At 120°C, maximum induction effect occurred at around a 40% blend ratio of ENR 50 and SMR L in the respective blends. For the filled stock at 140°C, carbon black exhibited less effect on the scorch property of the blends compared to silica.

Fatigue, resilience and hardness properties of unfilled SMR L/ENR 25 and SMR L/SBR blends

Abstract The fatigue, resilience and hardness properties of natural rubber/epoxidized natural rubber (SMR L/ENR 25) and natural rubber/styrene-butadiene rubber (SMR L/SBR) blends were studied with a blend ratio from 0 to 100% rubber. A semi-efficient vulcanization system was used throughout the study. The cure time of the rubber compound was determined by using the Moving-Die Rheometer (MDR 2000). The fatigue life of the unaged and aged samples was determined by using a Fatigue To Failure Tester (FTFT), whereas the unaged samples of resilience and hardness were measured by a Wallace Dunlop Tripsometer and a Wallace Dead Load Hardness Tester, respectively. Results indicate that before ageing, fatigue life passes through a maximum at 50% ENR and SBR for both blends. This observation is attributed to the “synergistic” effect of mutual reinforcement due to strain-induced crystallization in the former system, whereas for the latter system, compatibility accounts for the observed maximum. Ageing lowers the fatigue life for both blends, a phenomenon which is associated essentially with the breakdown of crosslinks. Resilience decreases with increasing blend ratio, whereas the reverse behaviour is observed for the hardness experiment.

CURING AND MECHANICAL PROPERTIES OF NITRILE AND NATURAL RUBBER BLENDS

The curing and mechanical properties of nitrile (NBR) and natural rubber (NR) blends were carried out. Two series of blends were prepared, i.e., NBR/SMR L and NBR/ENR 50 blends. Blends were prepared using a Brabender at a temperature of 60°C. Results indicate that the scorch time, t 2 and cure time, t 90 increase with increasing NBR content in both blends. In NBR/ENR 50 blends the increasing content of NBR increases the maximum elastic torque, torque difference, tan δ @ MH and viscous torque. However, in NBR/SMR L blends the opposite trend is observed for maximum elastic torque and torque difference. In both blends modulus at 100% elongation (M100) and at 300% elongation (M300) increases with increasing NBR content, whereas tensile strength and elongation at break show a decreasing trend.

Cure index and activation energy of vulcanization of natural rubber and epoxidized natural rubber vulcanized in the presence of antioxidants

The cure index and apparent activation energy of vulcanization of one grade of natural rubber (SMR L) and two grades of epoxidized natural rubbers (ENR 25 and ENR 50) were studied in the presence of three types of antioxidants [viz., 2,2′methylene-bis(4-methyl-6-tertbutylphenol) (AO 2246), poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), and N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD)] in the temperature range of 120–180°C by using a Monsanto automatic Mooney viscometer. Accelerated sulfur vulcanization system and up to 5 phr of antioxidant concentration was used throughout the investigation. Results indicate that both cure index and apparent activation energy of vulcanization are dependent on the type and concentration of the antioxidant used. AO 2246 (a phenol-based antioxidant) would retard vulcanization as reflected by the higher cure index and activation energy, an observation which is attributed to the solvation and steric hindrance effects of the antioxidant. On the contrary, both TMQ and IPPD (amine-based antioxidants) exhibit reverse behavior due to the catalytic effect of the antioxidants in generating more active sulfurating agents for vulcanization. In all cases, SMR L gives higher cure index and apparent activation energy than the corresponding ENR, a phenomenon which is associated with the activation of the adjacent double bond by epoxide group in the latter.

Mechanical and thermo-oxidative properties of blends of poly(vinyl chloride) with epoxidized natural rubber and acrylonitrile butadiene rubber in the presence of an antioxidant and a base

Being polar and compatible with poly(vinyl chloride), epoxidized natural rubber (ENR) is similar in behaviour to acrylonitrile butadiene rubber (NBR). To assess the extent of this similarity, the mechanical properties of 50/50 blends of PVC with these two rubbers were compared. Their response to thermo-oxidative ageing in the presence of an antioxidant and a base was also investigated by ageing the blends at 100°C for 7 days. Studies involving mechanical properties and FTIR were used to evaluate the extent of thermal degradation. The results revealed that blends of ENR show mechanical properties which are as good as, and in some instances better than, those of the NBR blends. However, the ENR blends with PVC are very prone to oxidative ageing. This might be attributed to the susceptibility of the oxirane group to ring-opening reactions, particularly in the presence of PVC, which yields HCI as it degrades. The amine-type antioxidant 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ) improved the oxidative stability of both blends. This was more significant in the ENR blend, which in some cases attained stability comparable with that of NBR. The addition of a base, calcium stearate [Ca(St) 2 ], did not show any influence in the PVC/ENR blend, even though it was expected to curb acid-catalysed degradation. Ca(St) 2 , however, improved the oxidative stability of the PVC/NBR blend. The combination of optimum amounts of TMQ and Ca(St) 2 effectively improved the tensile strength of both unaged blends, without appreciable adverse effect on elongation at break. This combination also imparted stability better than that of TMQ alone.

Recycled Polypropylene-Oil Palm Biomass: The Effect on Mechanical and Physical Properties

In this study, 25-year-old oil palm biomass (OPB) fiber—polypropylene (PP) composites are prepared by five different fiber loadings (10, 20, 30, 40, and 50%). The types of OPB used are oil palm empty fruit bunches, oil palm frond, and oil palm trunk. Transmission electron microscopy has confirmed that the cell wall structures of the various oil palm fibers have different cell wall thicknesses and exhibit the same ultrastructure as that of wood. The fibers consist of middle lamella, primary, and thick secondary walls with different thicknesses for different types of fibers. The secondary wall is differentiated into a S1 layer, a unique multi-lamellae S 2 layer, and a S3 layer. OPB fibers are compounded with PP using a Brabender DSK 42/7 twin screw extruder. The mechanical features such as tensile, flexural and impact properties of the OPB—PP composite are studied. The melt flow index (MFI) of the composite materials is also studied. Generally, the results show that lower fiber loading (10%) exhibits the highest tensile strength and MFI properties as compared to higher fiber loading (50%). Evidence of a fiber—matrix interphase is analyzed using scanning electron microscopy.

Effect of Test Rate on Adhesion Properties of SMR L, ENR-25 and ENR-50-based Pressure-Sensitive Adhesives

Abstract The dependence of loop tack, peel strength and shear strength of SMR L and Epoxidized Natural Rubber (ENR-25 and ENR-50)-based pressure sensitive adhesives on the rate of testing was investigated using coumarone-indene as the tackifying resin. Toluene and poly(ethylene terephthalate) (PET) were used as the solvent and substrate respectively throughout the study. A SHEEN hand coater was used to coat the adhesive on the substrate. All adhesion properties were determined with a Llyod Adhesion Tester operating at different rates of testing. Results show that loop tack, peel strength and shear strength all increase with increase in rate of testing, an observation which is attributed to the viscoelastic response of the adhesive which results in cohesive and adhesion failures at low and high test rates, respectively. Except for shear strength, the other adhesion properties increase with adhesive coating thickness. ENR-25-based adhesive consistently exhibits higher value compared to ENR-50 and SMR L. For shear strength, the largest value measured is for ENR-50 adhesive system.

Effect of Kaolin on Adhesion Property of Epoxidized Natural Rubber-based Pressure-sensitive Adhesive Using Gum Rosin as the Tackifier

The viscosity, loop tack, and peel strength of kaolin-filled epoxidized natural rubber (ENR 25 grade) adhesive was investigated using gum rosin as the tackifying resin. Kaolin loading was varied from 10—50 parts per hundred parts of rubber (phr), whereas the gum rosin concentration was fixed at 40 phr. Toluene was used as the solvent throughout the study. Polyethylene terephthalate substrate was coated at various adhesive coating thicknesses, i.e., 30, 60, 90, and 120 µm using a SHEEN hand coater. A HAAKE Rotary Viscometer Viscosity was used to measure the viscosity of the adhesive. Loop tack and peel strength were determined by a Llyod Adhesion Tester operating at 30 cm/min. Results show that viscosity of the adhesive increases gradually with increase of kaolin loading due to the concentration effect of the filler. Loop tack and peel strength, however, show maximum value at 20 phr and 30 phr kaolin, respectively, an observation which is attributed to the maximum wettability and compatibility of adhesive on the substrate.