Beng Teik Poh

TENSILE PROPERTY OF EPOXIDIZED NATURAL RUBBER/NATURAL RUBBER BLENDS

The tensile strength and elongation at break of epoxidized natural rubber (ENR) blended with natural rubber (NR) was studied. ENR 25, ENR 50, and one grade of natural rubber (SMR L) were used as the elastomers. The composition of ENR was varied from 0% to 100% rubber. The accelerated sulfur vulcanization system was used throughout the investigation. The tensile property of unaged and aged samples was determined by using the Monsanto tensometer (T10) operating at 50 cm/min. Results show that the tensile strength and elongation at break passes through a maximum at 50% ENR for both ENR25/SMR L and ENR50/SMR L blends. This positive deviation from ideality is attributed to the mutual reinforcement of ENR and NR in the blends as a result of strain-induced crystallization. This synergistic effect is more pronounced in the case of ENR 25 due to the higher crystallinity and availability of more double bonds, which is more compatible to NR compared to ENR 50/NR blends. For the aged samples, a drop in the tensile property associated to the breakdown of the polysulfidic cross-link during aging is observed. A systematic study of the effect of sulfur concentration on the percentage retention of tensile property of the ENR blends after aging reveals that percentage retention decreases with increasing sulfur loading, which, in turn, enhances the formation of the polysulfidic cross-link; thus, more breakdown is observed in the rubber vulcanizate.

Shear Strength of SMR—Based Pressure-Sensitive Adhesives

The shear strength of Standard Malaysian Rubber (SMR)-based pressure-sensitive adhesives was studied using coumarone-indene resin as the tackifier resin. Three grades of SMR, i.e., SMR L, SMR 10, and SMR 20 were used as the elastomers. The concentration of tackifier resin was varied from 0–80 parts per hundred parts of rubber (phr). Toluene was used as the solvent throughout the experiment to prepare the pressure-sensitive adhesives. A SHEEN hand coater was used to coat the adhesive on the polyethylene terephthalate substrate to give a coating thickness of 30, 60, 90, and 120 µm. Shear strength of the adhesive was determined by using a Texture Analyzer. Results indicate that for a fixed coating thickness, shear strength decreases gradually with increasing resin content for all the rubbers studied. This observation is attributed to the decreasing cohesive strength of adhesive as resin loading is increased. However, for fixed resin content, shear strength increases with increasing coating thickness suggesting that shear strength is thickness-dependent. SMR L consistently shows higher shear strength than SMR 10 and SMR 20 for all coating thickness, an observation, which is attributed to higher purity of SMR L, compared with the latter two rubbers. The shear strength passes through a maximum at 5 min of mastication time, after which it decreases gradually with further mastication.

Viscosity and Peel Strength of SMR 10-Based Pressure-Sensitive Adhesives

The viscosity and peel strength of a natural rubber-based pressure-sensitive adhesive was studied. One grade of natural rubber (SMR 10) and coumarone-indene resin were used as the elastomeric material and tackifier, respectively. Throughout the experiment, toluene was used as the solvent to prepare the adhesive. The effect of mastication time of rubber and tackifier concentration on the viscosity and peel strength of adhesive on various substrates was systematically investigated. The viscosity was measured using a HAAKE Rotary Viscometer. T-Test, 90° Adhesion To Steel (ATS), and 180° Adhesion To Steel (ATS) Tests were used to determine the peel strength of the adhesive. The results indicate that the viscosity of the adhesive increases with the resin content but decreases with mastication time. The peel strength generally increases with an increase in resin content except for the 20 min masticated sample. For all concentrations of the resin tackifier studied, the 10 min masticated sample exhibits the highest peel strength as compared to the corresponding values of the other masticated samples. This observation is attributed to the optimum wetting and formation of mechanical interlocking, and anchorage of the adhesive in pores and irregularities in the substrate for the former sample.

Synthesis and Characterization of Hydrophobically Modified Cationic Polyacrylamide with Low Concentration of Cationic Monomer

Hydrophobically modified cationic polyacrylamides were synthesized via free radical solution copolymerization using ammonium persulphate/sodium hydrogen sulphite as the redox initiator. Epichlorohydrin, acrylamide and trialkylamine were used to synthesize the hydrophobic cationic monomer 3-acrylamido-2-hydroxypropyltriakylammonium chloride (AHPTAAC) in which the trialkyl group was trihexylamine (AHPTHAC), trioctylamine (AHPTOAC) and tridodecylamine (AHPTDAC). Low concentration (1–6 mol%) of cationic monomer from each group were copolymerized with acrylamide to obtain hydrophobically modified cationic polyacrylamide. Results show that the intrinsic viscosity and molecular weight of the copolymers decreases with the concentration of the hydrophobic cationic group, whereas charge density indicates the reverse behaviour. Fourier Transform Infrared (FTIR) and Transmission Electron Microscopy (TEM) were also carried out to elucidate the structure of the copolymer.

Synthesis and Characterization of Hydrophobically Modified Cationic Acrylamide Copolymer

Abstract Hydrophobically modified cationic acrylamide copolymers were synthesized by free radical solution copolymerization using potassium persulfate as the initiator. Epichlorohydrin, acrylamide, and tridodecylamine were used to synthesize the hydrophobically modified cationic monomer, i.e., 3-acrylamido-2-hydroxypropyltridodecylammonium chloride (AHPTDAC), which was then copolymerized with acrylamide. The intrinsic viscosity, molecular weight, and charge density of the copolymers depend on the ratio of AHPTDAC and acrylamide used. Fourier transform-infrared (FT-IR) and transmission electron microscopy (TEM) were used to elucidate the structure of the copolymer. The solid copolymer is insoluble in water but only swells in the aqueous medium.

Viscosity and Peel Strength of Magnesium Oxide-Filled Adhesive Prepared from Epoxidized Natural Rubber (ENR 25)

Viscosity and peel strength of epoxidized natural rubber (ENR 25)-based adhesive was investigated in the presence of magnesium oxide. Petro resin and toluene were used as the tackifier and solvent, respectively. Viscosity was determined by a HAAKE Rotary Viscometer whereas peel strength was measured by a Lloyd Adhesion Tester. Results show that viscosity of adhesive increases with increasing magnesium oxide loading. However, for the peel strength, a maximum is obtained at 20 phr of magnesium oxide where maximum wettability and compatibility occurs. For a fixed filler concentration, peel strength increases with coating thickness for the three modes of peel tests.

The Effect of Silica on the Peel Adhesion of Epoxidized Natural Rubber-Based Adhesive Containing Coumarone-Indene Resin

The peel strength of silica filled on two grades of epoxidized natural rubber (ENR), i.e., ENR 25 and ENR 50 adhesive were investigated using coumarone-indene as the tackifying resin. Toluene was used as the solvent throughout the study. Result shows that peel strength increases with increase in silica loading due to the concentration effect of the filler. Peel strength, however, shows maximum value at 40 phr silica for both ENR 25 and ENR 50 an observation that is attributed to the maximum wettability and compatibility of adhesive on the substrate.

Effect of Blend Ratio on Adhesion Properties of Pressure-Sensitive Adhesives Prepared from SBR/SMR L Blends

The viscosity, tack, and peel strength of an SBR/SMR L-based pressure-sensitive adhesive was studied. Coumarone–indene resin and toluene were used as the tackifier and solvent, respectively, throughout the experiment. The blend ratio of SBR/SMR L was varied from 0 to 100% whereas the resin content was increased from 40 to 120 parts per hundred parts of rubber in the adhesive formulation. The viscosity was determined by a HAAKE rotary viscometer. Loop tack and peel strength of paper/polyethylene terephthalate film were measured using a Lloyd adhesion tester operating at 30 cm/min. Results show that the viscosity of the adhesive decreases with % SBR but increases with resin loading. Loop tack of adhesive indicates a maximum value at 20% SBR for all resin loadings. The peel strength, however, exhibits maximum value at 40% SBR for the three modes of peel tests, an observation which is attributed to the optimum wettability of adhesive on the substrate where formation of mechanical interlocking and anchorage of the adhesive in pores and irregularities in the substrate occurs.

Effect of Molecular Weight of Rubber on Tack and Peel Strength of SMR L-Based Pressure-Sensitive Adhesives using Gum Rosin and Petroresin as Tackifiers

Loop tack and peel strength of natural rubber (SMR L)-based pressure-sensitive adhesive were studied using five different molecular weights of SMR L. Gum rosin and petroresin were used as tackifiers, whereas toluene was chosen as the solvent throughout the experiment. A SHEEN hand coater was used to coat the adhesive on a polyethylene terephthalate (PET) substrate at a coating thickness of 30, 60, 90 and 120 μ m. Loop tack and peel strength were determined by a Llyod Adhesion Tester operating at 30 cm/min. Results show that maximum values of loop tack and peel strength were obtained at a molecular weight of 8.5 × 104, an observation which is attributed to maximum wettability of adhesive on the substrate. Loop tack and peel strength increases with coating thickness for all molecular weight of rubber and tackifiers studied.

Physicochemical and Rheological Properties of Novel Magnesium Salt-Polyacrylamide Composite Polymers

Two series of novel inorganic-organic composite polymers have been prepared through physical blending of magnesium chloride and magnesium hydroxide respectively with polyacrylamide aqueous solution. The physicochemical properties of the magnesium salt-polyacrylamide composite polymers were tuned by varying the ratio between the magnesium salt (e.g., magnesium chloride and magnesium hydroxide) and polyacrylamide. Characterizations of magnesium salt-polyacrylamide composite polymers were carried out via FTIR and TEM. Parameters such as solution conductivity and viscosity were also taken into account to characterize the physicochemical properties of the composite polymer aqueous solutions. Magnesium chloride-polyacrylamide (MCPAM) composite polymer aqueous solutions have a higher conductivity compared to magnesium hydroxide-polyacrylamide (MHPAM) composite polymer aqueous solutions. The viscosities of the MHPAM composite polymer aqueous solutions were found higher than MCPAM composite polymer aqueous solutions. The rheological properties of the composite polymer aqueous solutions were investigated using steady-state flow and oscillatory frequency sweep within the linear viscoelastic region. Shear-thinning effect was observed for both composite polymer systems when the shear rate increases. In oscillatory frequency sweep tests, both composite polymer systems show that the viscoelastic behaviors depend strongly on the magnesium salt concentrations. Viscous behavior was found to be dominant for both composite polymer systems.