THE EFFECTS OF A MULTIFUNCTIONAL ADDITIVE ON CURING CHARACTERISTICS,MECHANICAL PROPERTIES,AND SWELLING BEHAVIOR OF NATURAL RUBBER/POLYCHLOROPRENE RUBBER BLENDS

The effects of a diamine salt of fatty acid of general structure [RNH₂ ⁺[CH₂)₃NH⁺] [R′COO^?]₂ referred to as a multifunctional additive (MFA) on curing characteristics and mechanical properties and swelling behavior of natural rubber (SMR L) and polychloroprene (CR) rubber blends were studied. Compared to SMR L/CR blends without MFA, the incorporation of 2 phr (parts per hundred parts of rubber) of MFA in the blends increased mechanical properties, i.e., tensile strength, tensile modulus and hardness, and improved swelling resistance toward toluene and ASTM oil No. 1. However the scorch time, t ₅ and cure index, Δt _L decrease with incorporation of MFA into the blends.     

In situ epoxidized natural rubber: Improved oil resistance of natural rubber

This study sought to synthesize an in situ epoxidized natural rubber (NR) from 20% dry rubber content latex stabilized by nonionic surfactant, 5 phr of Terric 16A16, in the presence of hydrogen peroxide and formic acid at the temperature of 50°C. The molar ratios of H₂O₂ and HCOOH to isoprene unit were equal, 0.75 : 0.75. Reaction was carried out for 3 to 8 h. This reaction yielded products of various epoxide contents depending on reaction time. Based on DSC characterization, epoxide contents of the in situ epoxidized natural rubbers (ENRs) were about 22–39 mol %. Tensile properties and tear resistance of the in situ ENRs were equal to, or better than, those of NR and commercial ENRs. The in situ epoxidation improved resistance to petroleum ether, but not to toluene. Changes in volume and weight of specimens immersed in ASTM no. 3 oil and automobile oils (various trade names: Shell engine oil, Shell gear oil, and Toyota motor oil) exhibited significant decrease after epoxidation, except in Shell brake fluid. Similar results were obtained from tensile testing of the oil‐immersed specimens. Tensile strength and elongation at break of the in situ ENRs were much higher than those of NR after immersion in those oils at room temperature for 7 days, except the immersion in brake fluid. Improved oil resistance of the in situ ENRs under severe condition was obtained in gear oil. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 261–269, 2003     

The Comparison Effects of Palm Oil Fatty Acid and Stearic Acid on Dynamic Properties,Curing Characteristics and Mechanical Properties of Carbon Black Filled Epoxidized Natural Rubber Compounds

Abstract

The effects of palm oil fatty acid and stearic acid on dynamic properties, curing characteristics and mechanical properties of carbon black filled epoxidized natural rubber compounds were studied. It was found that the scorch time, t ₂ and cure time, t ₉₀ increased with increasing both acids concentrations. For dynamic properties, the maximum elastic torque, increased with acids concentration, whereas the minimum elastic torque shows a decreasing trend. Results also indicate that the decrease in viscous torque and tan δ is significant with increasing acids concentration. For tensile modulus, hardness, maximum torque-minimum torque and swelling index, results indicate that both acids have some effects on crosslink density. However tensile and tear strength pass through a maximum as the concentration of both acid increased.     

Vinyl acetate ethylene copolymer and nanosilica reinforced epoxidized natural rubber: Effects of sulfur curing systems on cure characteristics,tensile properties,thermal stability,dynamic mechanical properties and oil resistance

This study aimed at preparing nanocomposite from epoxidized natural rubber with about 40 mol% epoxidation (ENR40), vinyl acetate ethylene copolymer (VAE) contained about 70 wt% acetate groups and nanosilica (nSiO₂). Two parts by weight per hundred parts of rubber/resin of nSiO₂ were assembled to 80/20 (w/w) ENR40/VAE blend via latex blending. The resulting nanocomposite latex was coagulated before compounding with curing agents in an internal mixer. Tetrabenzylthiuram disulphide was used as a non‐carcinogenic accelerator in three sulfur vulcanization/curing systems, namely conventional (CV), semi‐efficient (semi‐EV) and efficient (EV) systems. The rubber compounds were sheeted on a two‐roll mill and press‐cured using a compression molding machine. Influence of curing systems on cure characteristics, tensile properties, thermal stability, dynamic mechanical properties and oil resistance of the nanocomposites was investigated. The results revealed that the CV system exhibited the highest crosslink density, tensile properties and storage modulus, while the EV system exhibited the longest scorch and cure time and the highest thermal stability and oil resistance. Moreover, the percentage retention of the tensile properties after thermal aging for CV system was lower than that of semi‐EV and EV systems. However, the pristine ENR40 and 80/20 (w/w) ENR40/VAE blend were also prepared for comparison. J. VINYL ADDIT. TECHNOL., 25:E28–E38, 2019. © 2018 Society of Plastics Engineers     

Palm oil fatty acid as an activator in carbon black filled natural rubber compounds: effect of vulcanization system

Carbon black filled natural rubber compounds were cured using conventional vulcanization (CV) and semi-efficient vulcanization (semi-EV) systems. The effect of palm oil fatty acid on cure characteristics and mechanical properties was examined. It was found that the cure time t₉₀, and scorch time increased with increasing palm oil fatty acid concentration in both systems. At fixed acid concentration, semi-EV compounds show shorter t₉₀ and scorch time than CV compounds. Results from tensile modulus, hardness, maximum torque-minimum torque M_HR-M_L, and swelling measurements indicate that palm oil fatty acid has some effect on crosslink density. At fixed palm oil fatty acid concentration, CV compounds have better mechanical properties (tensile modulus, hardness, tear and tensile strengths) compared with semi-EV compounds. ©1997 SCI     

Oil absorbents based on styrene–butadiene rubber

Four oil absorbents based on styrene–butadiene (SBR)—pure SBR (PS), 4‐tert‐butylstyrene–SBR (PBS), EPDM–SBR network (PES), and 4‐tert‐butylstyrene‐EPDM‐SBR (PBES)—were produced from crosslinking polymerization of uncured styrene–butadiene rubber (SBR), 4‐tert‐butylstyrene (tBS), and ethylene–propylene–diene terpolymer (EPDM). The reaction took place in toluene using benzoyl peroxide (BPO) as an initiator. Uncured SBR was used as both a prepolymer and a crosslink agent in this work, and the crosslinked polymer was identified by IR spectroscopy. The oil absorbency of the crosslinked polymer was evaluated with ASTM method F726‐81. The order of maximum oil absorbency was PBES > PBS > PES > PS. The maximum values of oil absorbency of PBES and PBS were 74.0 and 69.5 g/g, respectively. Gel fractions and swelling kinetic constants, however, had opposite sequences. The swelling kinetic constant of PS evaluated by an experimental equation was 49.97 × 10^?2 h^?1. The gel strength parameter, S, the relaxation exponent, n, and the fractal dimension, d_f, of the crosslinked polymer at the pseudo‐critical gel state were determined from oscillatory shear measurements by a dynamic rheometer. The morphologies and light resistance properties of the crosslinked polymers were observed, respectively, with a scanning electron microscope (SEM) and a color difference meter.     

Synthesis and characterization of maleated ionomers via ring‐opening reaction of epoxidized styrene‐butadiene rubber with potassium hydrogen maleate and study of their behavior as compatibilizer

A novel method for synthesizing maleate ionomer of (styrene‐co‐butadiene) rubber (SBR) from epoxidized SBR was developed. The epoxidized SBR was prepared via epoxidation of SBR with performic acid formed in situ by H₂O₂ and formic acid in cyclohexane. The maleated ionomer was obtained by ring‐opening reaction of the epoxidized SBR solution with an aqueous solution of potassium hydrogen maleate. The optimum conditions were studied. It was found that it is necessary to use phase transfer catalyst and ring‐opening catalyst for enhancing the epoxy group conversion. To obtain 100% conversion addition of dipotassium maleate is important. The product was characterized by FTIR spectrophotometry and transmission electron microcroscopy (TEM). The results showed that the product was really an ionomer with domains of maleate ionic groups. Some properties of the ionomer, such as water absorbency, oil absorbency and dilute solution behavior were studied. With increasing ionic groups, the water absorbency of the ionomer increases, whereas the oil absorbency decreases. The dilute solution viscosity of the ionomer increases abruptly with increasing ionic group content. The ionomer can be used as a compatibilizer for the blends of SBS and chlorosulfonated polyethylene (CSPE). Addition of a small amount of the ionomer to the blend can enhance the mechanical properties of the blends. 3 wt % ionomer based on the blend can increase the tensile strength and ultimate elongation of the blend nearly twice. The compatibility of the blends enhanced by adding the ionomer was shown by scanning electron microscopy. The blend of equal parts of SBS and CSPE compatibilized by the ionomer behaves as an oil resistant thermoplastic elastomer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 792–798, 2006     

Polylactic acid/ethylene glycol triblock copolymer as novel crosslinker for epoxidized natural rubber

Polylactic acid/ethylene glycol triblock copolymer (LLA₄₆EG₄₆LLA₄₆) was prepared and used in a crosslink process of epoxidized natural rubber (ENR) by employing a ring‐opening reaction using Sn(Oct)₂ as a catalyst. The OH‐capped copolymer acts as a macromolecular crosslinking agent in the formation of ENR networks, leading to drastic enhancement in tensile properties. Crosslink efficiency and chemical structures of the cured materials are examined by solvent fractionation, swelling experiments, XRD, ¹H‐NMR, and ATR‐FTIR spectroscopy. The efficiency of the curing process is dependent on the ENR/copolymer feed ratios. The degree of property improvement and gas permeability/selectivity behaviors of the cured materials are strongly dependent on the copolymer content and the efficiency of the curing process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ceramer coatings from castor oil or epoxidized castor oil and tetraethoxysilane

New inorganic-organic hybrids were synthesized through the reaction of castor oil (CO) or epoxidized castor oil (ECO) with tetraethoxysilane (TEOS). The mass proportions of ECO/TEOS varied from 90∶10 to 60∶40, and films of the material were thermally cured. An IR spectroscopy analysis was performed, and macro- and microscopic properties such as adhesion, hardness, swelling in toluene, microstructure (scanning electron microscopy), and T _g were investigated as a function of the proportion of their inorganic-organic precursor. Morphologic studies showed that the hybrid films were homogeneous when lower proportions of the inorganic precursors were used. Hardness and tensile strength increased with TEOS concentration, whereas swelling in toluene decreased with TEOS concentration. Good adhesion was observed throughout the hybrid series.     

THE COMPARISON PROPERTIES OF RECYCLE RUBBER POWDER,CARBON BLACK,AND CALCIUM CARBONATE FILLED NATURAL RUBBER COMPOUNDS

The effects of filler loading on the curing characteristics, swelling behavior, and mechanical properties of natural rubber compounds were studied using a conventional vulcanization system. Recycle rubber powder (RRP), carbon black (CB) (N550), and calcium carbonate (CaCO₃) were used as fillers and the loading range was from 0 to 50 phr. Results show that the scorch time, t ₂, and cure time, t ₉₀, decrease with increase in filler loading. At a similar filler loading, RRP shows shortest t ₂ and t ₉₀ followed by CB and calcium carbonate. The tensile strength, tensile modulus, and hardness increase with increase in CB loading, whereas elongation at break, resilience, and swelling properties show opposite trend. For RRP and calcium carbonate filled natural rubber compounds, the tensile strength increases up to 10 phr and starts to deteriorate at higher filler loading. The other properties such as tensile modulus, hardness, elongation at break, resilience, and swelling percentage show a small change (increase or decrease) with increase in RRP and calcium carbonate loading in natural rubber compounds. Overall results indicate that RRP can be used as a cheapener to replace calcium carbonate in natural rubber compounds where improved mechanical properties are not critical.     

Synthesis of sulfonated rubber ionomers by the ring‐opening reaction of epoxidized styrene–butadiene rubber,their characterization,and their properties

A novel method for the synthesis of the sulfonate ionomer of styrene‐co‐butadiene rubber (SBR) was developed. SBR was first epoxidized by performic acid formed from hydrogen peroxide and formic acid in situ in solution, and this was followed by a ring‐opening reaction with an aqueous solution of NaHSO₃. The optimum conditions for the epoxidation of SBR in the presence of a phase‐transfer catalyst and for the ring‐opening reaction of epoxidized SBR with an aqueous solution of NaHSO₃ were studied. During the epoxidation of SBR, a phase‐transfer catalyst, such as poly(ethylene glycol), could enhance the conversion of double bonds to epoxy groups. During the ring‐opening reaction, both the phase‐transfer catalyst and ring‐opening catalyst were necessary to enhance the conversion of the epoxy groups to ionic groups. The addition of Na₂SO₃ to the reaction mixture was important to obtain 100% conversion. The products were characterized with Fourier transform infrared spectrophotometry, ¹H‐NMR spectroscopy, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). DSC showed that the sodium sulfonate SBR ionomer possessed a dissociation temperature of ionic domains at 110°C, which appeared as black spots under TEM, after the sodium ions of the ionomer were substituted by lead ions. Some properties of the sodium ionomer, such as the water absorbency, oil absorbency, and dilute solution behavior, were studied. With increasing ionic groups, the water absorbency of the ionomer increased, whereas the oil absorbency decreased. The dilute solution viscosity of the ionomer increased abruptly with increasing ionic group content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3090–3096, 2006     

Role of geopolymer as a cure activator in sulfur vulcanization of epoxidized natural rubber

Geopolymer (GP) was synthesized and used as activators in sulfur vulcanization of epoxidized natural rubber (ENR). Influences of GP on cure characteristics, crosslink density, mechanical, thermal, and morphological properties were investigated and compared to the conventional rubber formulation with ZnO activator. The ZnO is a hazardous chemical for the environment and has proclaimed that its application in rubber technology should be reduced and controlled. It was found that the GP-activated ENR compounds showed significantly higher vulcanization rate than cases with the conventional ZnO compound. This was indicated by the GP activated compounds having shorter scorch time, cure times, and lower activation energy but higher cure rate index (CRI). Also, the GP activated ENR compounded with stearic acid exhibited the highest conversion. This matches well the highest torque difference and crosslink density, observed by temperature scanning stress relaxation (TSSR) and swelling measurements. Furthermore, the GP-activated vulcanizate had better thermal stability than the ZnO-activated ENR material. In addition, the GP-activated ENR vulcanizate with stearic acid exhibited high 100% moduli, tensile strength, and hardness. This proves that GP has a high potential for use as activators in sulfur vulcanization of rubber compounds, as an alternative to the conventional ZnO. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48624.     

Influence of internal strain on change of crosslink density of natural rubber vulcanizates by thermal ageing

Change of crosslink density of natural rubber (NR) vulcanizates by thermal ageing at 60 °C has been studied under swollen conditions in solvents to investigate the influence of internal strain applied to the vulcanizate on the crosslink density change. The internal strain was controlled by swelling with various solvents such as n‐hexane, toluene, tetrahydrofuran (THF), methanol and water. The order of degree of the swelling is toluene ≈ THF > n‐hexane > methanol > water. The influence of curing system has been investigated with the vulcanizates cured by the conventional and EV cure systems. After thermal ageing, the apparent crosslink densities of the swollen vulcanizates in n‐hexane, toluene and THF decrease irrespective of the cure systems, while that of the swollen vulcanizate in water increases. For the swollen vulcanizates in methanol, the apparent crosslink density of the vulcanizate with the conventional cure system after thermal ageing increases while that of the vulcanizate with the EV cure system decreases. The decrement of the apparent crosslink density of the vulcanizate after thermal ageing becomes larger and larger upon increasing the internal strain. © 2001 Society of Chemical Industry     

Phosphorus modification of epoxidized liquid natural rubber to improve flame resistance of vulcanized rubbers

The use of phosphorus for improving flame retardancy of natural rubber vulcanizates was attempted by incorporating a modified form of natural rubber. By reacting epoxidized liquid natural rubber (ELNR) with dibutylphosphate it was possible to chemically modify the polymer. On a 25% epoxidized LNR, 5.2–6.8% w/w of phosphorus could be fixed on the polymer backbone. The reaction carried out in bulk and solution resulted in products with different T_g values probably due to the varying crosslink levels in the resultant products. Chemical analysis of the modified polymers prepared by two sets of reactions under identical conditions proved the reproducibility of the reactions in bulk and in solution. Incorporation of the phosphorus-modified ELNR in a natural rubber formulation decreased the flammability behaviors of the vulcanizate. On the other hand, a decrease of the rate of curing and mechanical properties was observed. The phosphorus addition could also be carried out by mixing ELNR and dibutylphosphate at the time of mixing the compounds and resulted in equally good flame retardance with relatively better processing and mechanical properties. © 1994 John Wiley & Sons, Inc.     

Processability characteristics and physico‐mechanical properties of natural rubber modified with rubber seed oil and epoxidized rubber seed oil

The processability characteristics and physico‐mechanical properties of natural rubber (NR) modified with raw rubber seed oil and epoxidized rubber seed oil have been studied. The modified mixes showed higher scorch time and lower cure rate, crosslink density, and ultimate state of cure compared to an unmodified mix. The thermal stability of the vulcanizates was practically unaffected by the modification. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1413–1418, 2000     

Porous rubber cryogels: effect of the gel preparation temperature

This paper examines the effect of the gel preparation temperature (T _prep) on the physical properties of the rubber-based macroporous organogels prepared by solution crosslinking in benzene at subzero temperatures. Cis-polybutadiene (CBR) and styrene-butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride (S₂Cl₂) was the crosslinker in the gel preparation. It was shown that T _prep is an extremely important parameter to adjust the porous structure and thus, the cryogel properties. The networks formed by CBR and SBR showed an aligned porous structure with an exception of honey-comb structured porous SBR cryogels prepared at ?2 °C. 10¹- to 10²-μm sized regular pores of the networks caused by the benzene crystals act as a template during gelation, separated by 10–20 μm pore walls in thickness. They exhibit fast swelling and deswelling properties as well as reversible swelling–deswelling cycles in toluene and methanol, respectively. The ability of the organogels for the removal of petroleum products from aqueous solutions was also demonstrated using diesel and crude oil as model pollutants. In addition, the reusability of the organogels and their continuous sorption capacities were checked by repeated sorption–squeezing cycles. All the tests showed that the aligned porous organogels are suitable materials for the oil spill cleanup procedures.     

High oil‐absorptive composites based on 4‐tert‐butylstyrene‐EPDM‐divinylbenzene graft polymer

4‐tert‐Butylstyrene‐EPDM‐divinylbenzene graft polymer (PBED) was prepared by graft crosslinking polymerization in toluene using BPO as an initiator. Gel and sol of PBED were isolated by extraction with tetrahydrofuran (THF). Sol PBED can be reused as oil absorbent through cross‐linking by ultraviolet irradiation. After swelling in oil, crosslinked polymers have poor gel strength to be taken out of oil wholly at high absorbency, although they possess strong mechanical strength in their dry states. As known, composite technique is one of the useful methods for material reinforcement. Fibres, sponges and non‐woven fabrics were used as reinforcers or supporters in this work. Oil absorbency was measured by method ASTM (F726‐81) and swelling kinetics of the composite was evaluated by an experimental equation. The gel strength parameter S, the relaxation exponent n, and the fractal dimension d_f of polymer and some composites in pseudo‐critical gel state were determined from oscillatory shear measurements by a dynamic rheometer. Mechanical properties and the morphologies of some composites were measured with a tensile tester and scanning electron microscopy, respectively. © 2001 Society of Chemical Industry     

Biobased composite resins design for electronic materials

Biobased materials developed from triglycerides contain a large variety of structures, which makes it difficult to predict their properties. In this study, we used a structure–property relation to design biobased materials, both theoretically and experimentally. A general equation to predict the crosslink density in terms of the level of chemical functionalities of the triglycerides was derived and used as a design rule for high‐crosslinked polymer materials. The twinkling fractal theory and the Clausius–Mossotti equation were used to guide two approaches of synthesis to improve the properties of the biobased thermosets: the biobased resin acrylated epoxidized soybean oil (AESO) was either crosslinked with divinylbenzene (DVB) or chemically modified by phthalic anhydride. The DVB‐crosslinked resins had a 14–24°C increase in their glass‐transition temperatures (T_g′s), which was dependent on the crosslink densities. T_g increased linearly as the crosslink density increased. Phthalated acrylated epoxidized soybean oil (PAESO) had an 18–30% improvement in the modulus. The dielectric constants and loss tangents of both DVB‐crosslinked AESO and PAESO were lower than conventional dielectrics used for printed circuit boards (PCBs). These results suggest that the new biobased resins with lower carbon dioxide footprint are potential replacements for commercial petroleum‐based dielectric materials for PCBs. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Quantitative analysis for reaction between epoxidized natural rubber and poly (L‐lactide) through 1H‐NMR spectroscopy

Reaction between epoxidized natural rubber and poly(L ‐lactide) (PLLA) was investigated quantitatively in terms of conversion of the epoxidized natural rubber. The epoxidized natural rubber was prepared by epoxidation of high ammonia natural rubber (HA‐NR) or deproteinized natural rubber (DPNR) with peracetic acid followed by depolymerization with ammonium persulfate. The resulting liquid HA‐NR having epoxy group (LENR) or liquid DPNR having epoxy group (LEDPNR) were subjected to heating at 473 K for 20 min, after blending with PLLA. The products were characterized through morphology observation, DSC measurement, and ¹H‐NMR spectroscopy. The conversions of the rubbers were estimated from intensity ratio of signals in ¹H‐NMR spectrum for the products after removing unreacted rubber with toluene. Difference in the estimated conversion between the LENR/PLLA and LEDPNR/PLLA blends was interpreted in relation to proteins present in the rubber. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solubility parameters of polymers from swelling measurements at 60°C

The swelling behavior of the networks of natural rubber, an epoxidized natural rubber, low-density polyethylene, polystyrene, and poly(methyl methacrylate) are studied in six classes of solvents at 60°C. The data of the swelling coefficient are successfully treated by a modified version of the empirical equation proposed by Gee, as to determine the solubility parameter of a polymer, δ₂. It is found that increasing the temperature would decrease the δ₂'s of these polymers with a common rate of 0.02 (J/mL)^1/2/K. A semiempirical model is proposed to rationalize the present finding satisfactorily. © 1995 John Wiley & Sons, Inc.