Thermal and mechanical properties of aminopropoxylate-cured epoxy matrices

Bisphenol A diglycidyl ether–aminopropoxylate mixtures have been characterized with respect to their viscosities in the presence and absence of butanediol diglycidyl ether (reactive diluent), and their curing patterns have been studied at room temperature with or without 2,4,6-tris(dimethylaminomethyl)phenol (initiator/accelerator). A priori, these mixtures are expected to provide low connectivities to infinite networks at gelation, a prediction supported by the multiple glass-transition-temperature (T_g) behaviour of their cured forms. The effect of the aminopropoxylate curing agent chemistry/functionality, and the presence or absence of accelerator and reactive diluent on the tensile and impact behaviour of cured materials, is reported. An expectation of increased importance of polymerization with increases in the initiator/accelerator levels, alongside epoxy–amine addition reactions, has not been evidenced by the mechanical measurements. For diglycidyl ether bisphenol A–aminopropoxylate epoxy systems, in the glycidyl ether/reactive hydrogen molar ratio range 0·80 (set A) to 1·95 (set B), the tensile failure mode is brittle fracture. For the set A formulations, this mode of failure persists up to reactive diluent loadings of 1·01wt% based on the weight of bisphenol A diglycidyl ether. Beyond 1·01wt% reactive diluent loadings, the set A formulations show ductile failure with yielding; the tensile toughness increases with increases in reactive diluent levels. For the set B formulations, and for all reported loading levels of reactive diluent, the castings failed in brittle fashion with pronounced cavitation and stress whitening. © 1998 Society of Chemical Industry     

High‐performance bio‐based poly(lactic acid)/natural rubber/epoxidized natural rubber blends: effect of epoxidized natural rubber on microstructure,toughness and static and dynamic mechanical properties

Attempts have been made to prepare high‐performance bio‐based blends through blending of poly(lactic acid) (PLA) with natural rubber (NR) in the presence of epoxidized natural rubber (ENR) as a compatibilizer. The prepared samples were characterized using differential scanning calorimetry, measuring the tensile properties and impact resistance, scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMTA). Morphological studies revealed a matrix‐dispersed morphology for all blends, in which the average droplet size significantly decreased with the use of ENR. The elongation at break and impact strength of the blend containing 3 wt% ENR were 45 and 16 times those of neat PLA, respectively. These values are significantly higher than those previously reported for various simple and dynamically vulcanized rubber‐toughened PLAs. The influence of ENR on compatibility was confirmed by rheological tests, FTIR spectra and DMTA. DMTA also showed a marked increase in elastic modulus for the blend in the presence of 3 wt% ENR. The tensile properties and impact resistance were directly dependent on the ENR content and rubber droplet size. © 2018 Society of Chemical Industry     

Toughening of epoxy hybrid nanocomposites modified with silica nanoparticles and epoxidized natural rubber

Silica nanoparticles (SN) and epoxidized natural rubber (ENR) were used as binary component fillers in toughening diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine. For a single component filler system, the addition of ENR resulted in significantly improved fracture toughness (K_IC) but reduction of glass transition temperature (T_g) and modulus of epoxy resins. On the other hand, the addition of SN resulted in a modest increase in toughness and T_g but significant improvement in modulus. Combining and balancing both fillers in hybrid ENR/SN/epoxy systems exhibited improvements in the Young’s modulus and T_g, and most importantly the K_IC, which can be explained by synergistic impact from the inherent characteristics associated with each filler. The highest K_IC was achieved with addition of small amounts of SN (5 wt.%) to the epoxy containing 5–7.5 wt.% ENR, where the K_IC was distinctly higher than with the epoxy containing ENR alone at the same total filler content. Evidence through scanning electron microscopy (SEM) and transmission optical microscopy (TOM) revealed that cavitation of rubber particles with matrix shear yielding and particle debonding with subsequent void growth of silica nanoparticles were the main toughening mechanisms for the toughness improvements for epoxy. The fracture toughness enhancement for hybrid nanocomposites involved an increase in damage zone size in epoxy matrix due to the presence of ENR and SN, which led to dissipating more energy near the crack-tip region.     

Molecular-level dispersion of graphene into epoxidized natural rubber: Morphology,interfacial interaction and mechanical reinforcement

The interfacial interaction of composites dominates the properties of polymeric/inorganic nanocomposites. Herein, epoxy and hydroxyl groups are introduced into the natural rubber (NR) molecular chains to anchor oxygenous functional groups on the surface of graphene oxide (GO) sheets and therefore enhance the interfacial interaction between GO and rubber. From the morphological observation and interaction analysis, it is found that epoxidized natural rubber (ENR) latex particles are assembled onto the surfaces of GO sheets by employing hydrogen bonding interaction as driving force. This self-assembly depresses restacking and agglomeration of GO sheets and leads to homogenous dispersion of GO within ENR matrix. The formation of hydrogen bonding interface between ENR and GO demonstrates a significant reinforcement for the ENR host. Compared with those of pure ENR, the composite with 0.7 wt% GO loading receives 87% increase in tensile strength and 8.7 fold increase in modulus at 200% elongation after static in-situ vulcanization.     

Modification of epoxidized natural rubber as a PLA toughening agent

In the present study, the modification of epoxidized natural rubber (ENR) was investigated to improve toughness of PLA. ENR-PLA copolymers were synthesized by 2 steps reactions. Acid hydrolysis of ENR to prepare macroinitiator (ENR-OH) and copolymerization with lactide to obtain ENR-PLA copolymers. The reaction time of acid hydrolysis and the lactide monomer loading was investigated. The optimum conditions were 8 h acid hydrolysis with 5wt% lactide loading to obtain ENR8-PLA5 copolymers. A series of samples of PLA blended with ENR-PLA copolymers was prepared using melt-blending. The blend of PLA with ENR8-PLA5 copolymers at 1 phr substantially improved the tensile properties. The elongation at break was increased 67%, and toughness was increased 64% compared to neat PLA. These results indicate that ENR8-PLA5 has potential as toughening agent for PLA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48267.     

环氧化天然橡胶与白炭黑及Si 69之间的反应及其对白炭黑填充溶聚丁苯橡胶性能的影响

研究了环氧化天然橡胶(ENR)与白炭黑及改性剂Si 69之间的反应及其对白炭黑/溶聚丁苯橡胶复合材料中白炭黑的分散状况以及复合材料力学性能的影响。结果表明,ENR中的环氧基团开环与白炭黑发生反应,但不能开环与Si 69发生反应。由于ENR与白炭黑的反应速率较慢,导致ENR改性白炭黑在溶聚丁苯橡胶混炼胶与硫化胶中的分散状况有所不同。但是将ENR和Si 69同时加入到白炭黑/溶聚丁苯橡胶复合材料中后,与只用Si 69改性白炭黑填充的溶聚丁苯橡胶相比,硫化胶的拉伸强度基本不变,定伸应力、硬度和撕裂强度增大,扯断伸长率和拉伸永久变形减小,这是因为加入ENR和Si 69后即存在白炭黑与ENR及白炭黑与Si 69两种反应,并且ENR中的环氧基团可以活化其相邻的双键,加速硫化,从而导致硫化胶交联密度增大的缘故。     

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.     

The Effect of Filler Loading and Epoxidation on Paper-Sludge-Filled Natural Rubber Composites

The effect of filler loading and epoxidation on curing characteristics, dynamic properties, tensile properties, morphology, and rubber-filler interactions of paper-sludge-filled natural rubber compounds have been studied. Two different types of natural rubber, SMR L and ENR 50, having 0% and 50% of epoxidation and conventional vulcanization were used. Paper sludge was used as a filler and the loading range was from 0 to 40 phr. Compounding was carried out using a laboratory-sized two-roll mill. The scorch time for both rubber compounds decreased with filler loading. The cure time was found to decrease with increasing filler content for SMR L vulcanizates, whereas for ENR 50, the cure time seemed to be independent of the filler loading. Dynamic properties, i.e., maximum elastic torque, viscous torque, and tan delta, increase with filler loading in both grades of natural rubber. Results also indicate that both rubbers show increment in tensile modulus but inverse trend for elongation at break and tensile strength. However, for a fixed filler loading, ENR 50 compounds consistently exhibit higher maximum torque, modulus at 100% elongation, and modulus at 300% elongation, but lower elongation at break than SMR L compounds. In the case of tensile strength, ENR 50 possesses higher tensile strength than SMR L at 10 to 20 phr, but the difference is quite small at 30 and 40 phr. These findings might be associated with better rubber-filler interaction between the polar hydroxyl group of cellulose fiber and the epoxy group of ENR 50.     

Epoxidized natural rubber/epoxy blends: Phase morphology and thermomechanical properties

Epoxidized natural rubbers (ENRs) were prepared. ENRs with different concentrations of up to 20 wt % were used as modifiers for epoxy resin. The epoxy monomer was cured with nadic methyl anhydride as a hardener in the presence of N,N‐dimethyl benzyl amine as an accelerator. The addition of ENR to an anhydride hardener/epoxy monomer mixture gave rise to the formation of a phase‐separated structure consisting of rubber domains dispersed in the epoxy‐rich phase. The particle size increased with increasing ENR content. The phase separation was investigated by scanning electron microscopy and dynamic mechanical analysis. The viscoelastic behavior of the liquid‐rubber‐modified epoxy resin was also evaluated with dynamic mechanical analysis. The storage moduli, loss moduli, and tan δ values were determined for the blends of the epoxy resin with ENR. The effect of the addition of rubber on the glass‐transition temperature of the epoxy matrix was followed. The thermal stability of the ENR‐modified epoxy resin was studied with thermogravimetric analysis. Parameters such as the onset of degradation, maximum degradation temperature, and final degradation were not affected by the addition of ENR. The mechanical properties of the liquid‐natural‐rubber‐modified epoxy resin were measured in terms of the fracture toughness and impact strength. The maximum impact strength and fracture toughness were observed with 10 wt % ENR modified epoxy blends. Various toughening mechanisms responsible for the enhancement in toughness of the diglycidyl ether of the bisphenol A/ENR blends were investigated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39906.     

Studies on polyamide‐6/polyolefin blend system compatibilized with epoxidized natural rubber

Infrared spectra of polyamide‐6 (PA6) with and without epoxidized natural rubber (ENR) are presented. The influence of ENR used as a compatibilizer on the morphologies, crystallizability, mechanical properties, and thermal behavior of the polyamide‐6/polyolefins (PO) blends are studied. The infrared spectra suggest that under normal processing conditions, the carboxyl end groups of PA6 could chemically react in situ with the epoxy groups of ENR, and ester groups are created. This means that the PA6‐ENR grafting copolymer could be obtained during processing. All the morphological characterizations and thermal analyses show that the compatibility of PA6/PO blends is obviously improved by ENR because the copolymer increases the interaction between PA6 and PO. It is also found that the toughness of PA6/PO blends increase significantly after using ENR, while the tensile strength and the softening temperature of PA6/PO blends have almost no change. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 398–403, 2003     

Improving adhesion properties between rubber compound and brass-plated steel cord by the addition of epoxidized natural rubber to rubber compound

The adhesion between a rubber compound containing epoxidized natural rubber (ENR) and a brassplated steel cord was studied to shed light on the role of ENR for the improvement of adhesion. The addition of ENR in the rubber compound caused cure rate to decrease, and as ENR loading increased, modulus and hardness increased while tensile strength and elongation at break decreased. An improvement of adhesion was obvious with low loading of ENR at the range of 2 phr, while an adverse effect was observed with higher concentrations of 10 phr. Since the ratio of sulfur to copper at the interphase of the rubber compound/brass film adhesion sample increases with increased ENR loading up to 2 phr, the acceleration of sulfide formation by ENR could be proven. Adequate curing of rubber and the formation of high-molecular layer at the interphase by addition of small amount of ENR improve adhesion. However, the toughening of the rubber caused by the addition of larger amounts of ENR degrades the adhesion due to the poor physical properties of the rubber compound.     

Effect of latex concentration on epoxidation of natural rubber (NR) latex

Effect of latex concentration on the extent of epoxidation and physical properties of epoxidized natural rubber (ENR) was evaluated as a function of latex concentration in the range of 20–60% by weight. The epoxidation rate increased with increasing latex concentration. Physical properties and sequence distribution of an epoxy group of ENR with 30 mol % epoxy content was invariant with the latex concentration employed for epoxidation.     

Curing Characteristics and Mechanical Properties of Oil Palm Wood Flour Reinforced Epoxidized Natural Rubber Composites

Abstract

The paper reports on the curing characteristics and mechanical properties of oil palm wood flour (OPWF) reinforced epoxidized natural rubber (ENR) composites. Three sizes of OPWF at different filler loadings were compounded with a two roll mill. The cure (t ₉₀) and scorch times of all filler size decrease with increasing OPWF loading. Increasing OPWF loading in ENR compound resulted in reduction of tensile strength and elongation at break but increased tensile modulus, tear strength and hardness. The composites filled with smaller OPWF size showed higher tensile strength, tensile modulus and tear strength. Scanning electron microscope (SEM) micrographs showed that at lower filler loading the fracture of composites occurred mainly due to the breakage of fibre with minimum pull-out of fibres from the matrix. However as the filler loading is increased, the fibre pull-out became very prominent due to the lack of adhesion between fibre and rubber matrix.     

Improved cure characteristics and mechanical properties of an epoxidized natural rubber filled with cerium oxide nanoparticles: Influence of epoxide levels and filler loading

In this study, cerium oxide nanoparticles (nanoceria, CeNP) were used as a nanofiller in epoxidized natural rubber with varying epoxide levels, including 25% epoxidation (ENR-25) and 50% epoxidation (ENR-50). Co-precipitation methods were employed to synthesize a pure phase of CeNP with an average particle size of 11.4 ± 2.0 nm. CeNP was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. The effect of CeNP loading with 0–3 parts per hundreds of rubber (phr) on the properties of rubber nanocomposites was explored. ENR-25 nanocomposites with 1 phr of CeNP exhibited higher tensile strength and elongation at break compared to ENR-50 nanocomposites. These findings correspond to a lower Payne effect, improved scorch safety, and better processability. The strongest and most effective CeO₂–ENR interactions via silane linkages are expected to outperform sulfur crosslinking in ENR-25 having 1 phr of CeNP. Microstructural evaluation of an ENR-25 sample containing 1 phr of CeNP indicated well-distributed nanofillers in the ENR-25 matrix, indicating that CeNP and ENR-25 appeared to be well-matched. Hardness of all ENR nanocomposites increased with CeNP loading. The cracking resistance, creep properties, and thermal stability of rubber nanocomposites were unaffected by addition of CeNP in the ENR-25 and ENR-50 samples.     

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     

Effect of carbon black on self‐crosslinking network structure of polychloroprene rubber and epoxidized natural rubber blends

The goal of this research is to improve poor network structure of polychloroprene rubber (CR)/epoxidized natural rubber (ENR) self‐crosslinking blends, which could substitute traditional vulcanizates in some application area. Carbon black (CB)–CR/ENR blends were prepared by reacting CR with ENR in the presence of CB. The structure of CR/ENR blends was characterized by attenuated total‐reflectance Fourier transform infrared spectroscopy (FTIR‐ATR). The effect of CB loading on curing characterization and mechanical properties of CR/ENR blends was investigated, and the interaction among CR, ENR, and CB was studied using differential scanning calorimetry. The effect of CB loading on the Payne effect of CR/ENR was investigated using rubber process analyzer. Scanning electron microscope was used to characterize the morphology of CB–CR/ENR blends. The results showed that CR/ENR blends were obtained by the ring‐opening reaction of epoxy groups in ENR and chlorine groups in CR. Mechanical properties of CR/ENR blends increased with the increase of CB loading. The Payne effect of CR/ENR became more remarkable with increasing CB loading. Morphology study indicated that interfacial compatibility between CR and ENR increased with the increase of CB loading because CB could strengthen the self‐crosslinking network structure of CR/ENR blends. The promoting effect of CB on self‐crosslinking reaction was verified by the assessment of crosslink density. POLYM. COMPOS., 38:463–471, 2017. © 2015 Society of Plastics Engineers     

Effects of hygrothermally decomposed polyurethane on the curing and mechanical properties of carbon black‐filled epoxidized natural rubber vulcanizates

Hygrothermally decomposed polyurethane (HD‐PUR) was mixed up to 20 phr in epoxidized natural rubber (with 50 mol % epoxidation; ENR50) recipes, and the curing and mechanical behaviors were studied. Mechanical testing of the ENR50/HD‐PUR vulcanizates determined the tensile, tear, compression‐set, hardness, abrasion, hysteresis, and resilience properties. No significant changes were observed in the tensile properties with the incorporation of HD‐PUR. The ENR50 compounds showed an increase in compression set with increasing HD‐PUR content. Rubbers cured by a semi‐efficient vulcanization system gave the best overall performance. A further improvement in curing and mechanical properties was achieved by the carbon black grade N330 being replaced with a more active grade (N375). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2265–2276, 2002     

The effect of epoxide content on compatibility of poly(lactic acid)/epoxidized natural rubber blends

The objective of this work was to determine the effect of the epoxide content in epoxidized natural rubber (ENR) on the miscibility and compatibility with poly(lactic acid) (PLA) in prepared PLA/ENR blends. PLA was blended with 10 wt% of ENRs (epoxidized at 10, 15, 20, and 25 mol%). The presented study showed that the in situ graft copolymer, PLA-g-ENR, was formed during melt blending in the blends containing 10 and 15 mol% ENR. This work is the initial study showing the presence of PLA-g-ENR in the blends by ¹H-NMR and ¹³C-NMR. PLA-g-ENR acted as a compatibilizer, producing a partially miscible blend, indicated by an inward shift of the α-transition temperatures of PLA and ENR in the blends. PLA-g-ENR also greatly reduced the particle size of ENR and increased the impact strength, tensile strength, and elongation at break of the blends. The epoxide content of ENR changed deformation mechanisms of the blends.     

Effect of stearic acid concentration on the reversion behavior of epoxidized natural rubber

The effect of stearic acid concentration on the reversion behavior of epoxidized natural rubber (ENR 25 and ENR 50) was carried out in the temperature range of 150–180°C and 0.5–14.5 phr of stearic acid loading. Three common accelerators; namely, zinc dimethyldithiocarbamate (ZDMC), tetramethylthiuram disulfide (TMTD), and N-morpholinylbenzothiazole-2-sulfenamide (MBS) and conventional sulfur vulcanization system was used throughout the study. A Monsanto oscillating-disk rheometer was used to determine the reversion behavior of the rubber. Results indicate that for all the accelerators used, reversion decreases with increasing stearic acid concentration. The rate of decrease is more gradual up to about 6.5 phr of stearic acid, after which a rapid drop of reversion is observed for both ENR 25 and ENR 50. This observation is attributed to the increasing amount of mono- and disulfidic crosslinks as a result of desulfuration of polysulfidic crosslinks. The higher the stearic acid loading, the greater is the retardation effect on vulcanization; that is, more time is available for desulfuration. Increasing temperature would increase the reversion of the rubber vulcanizate because of the increase in thermal energy to decompose more crosslinks, including mono- and ether crosslinks for temperature higher than 160°C. ZDMC (an ultrafast accelerator) gives a higher reversion than MBS (a delay-action accelerator), because desulfuration occurs more slowly in the former system. The observed decrease in reversion as stearic acid concentration increases is technologically importance, because the aging property of the rubber vulcanizate is significantly improved. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1165–1169, 1999     

Physical properties and cure characteristics of natural rubber/nanoclay composites with two different compatibilizers

The effects of epoxidized natural rubber (ENR) and maleic anhydride‐grafted polybutadiene (PB‐g‐MA) as compatibilizers to rubber formulations with and without organo‐modified layered silicates are investigated. The physical properties and curing characteristics of composites are studied by moving die rheometer, rubber process analyzer, tensile, tear, and hardness testing. The state of organoclay intercalation was determined by X‐ray diffraction method. The addition of compatibilizers, especially ENR 50, results in further intercalation or exfoliation of the organoclay that increased the clay dispersion in the rubber matrix. ENR 50 with organo‐modified clay improves the physical properties and changes the curing profile. The addition of PB‐g‐MA without organoclay increases the tensile strength (σ_max) by increasing the stock viscosity of the rubber compound. Interestingly, simultaneous increase in hardness and σ_max is achieved in the presence of both compatibilizers, a characteristic that is difficult to achieve and sometimes required in rubber processing. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011