Toughening of dicyandiamide-cured DGEBA-based epoxy resins by CTBN liquid rubber

Toughening of a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin with liquid carboxyl-terminated butadiene acrylonitrile (CTBN) copolymer has been investigated. For this purpose six blend samples were prepared by mixing DGEBA with different concentrations of CTBN from 0 to 25 phr with an increment of 5 phr. The samples were cured with dicyandiamide curing agent accelerated by Monuron. The reactions between oxirane groups of DGEBA and carboxyl groups of CTBN were followed by Fourier-transform infrared (FTIR) spectroscopy. Tensile, impact, fracture toughness and dynamic mechanical analysis of neat as well as the modified epoxies have been studied to observe the effect of CTBN modification. The tensile strength of the blend systems increased by 26 % when 5 phr CTBN was added, and it remained almost unchanged up to 15 phr of CTBN. The elongation-at-break and Izod notched impact strength increased significantly, whereas tensile modulus decreased gradually upon the addition of CTBN. The maximum toughness of the prepared samples was achieved at optimum concentration of 15 phr of CTBN, whereas the fracture toughness (K _IC) remained stable for all blend compositions of more than 10 phr of CTBN. The glass transition temperature (T _g) of the epoxy resin significantly increased (11.3 °C) upon the inclusion of 25 phr of CTBN. Fractured surfaces of tensile test samples have been studied by scanning electron microscopic analysis. This latter test showed a two-phase morphology where the rubber particles were distributed in the epoxy resin with a tendency towards co-continuous phase upon the inclusion of 25 phr of CTBN.     

Mechanical behavior and structure of rubber modified vinyl ester resins

Vinyl esters are used widely as thermoset matrix materials for reinforced composites; however, they suffer from low‐impact resistance. Substantial enhancement of the toughness of brittle polymers may be achieved by dispersing elastomeric inclusions or rubber particles in the polymer matrix, inducing multiple crazing and shear yielding of the matrix. The main objectives of this work are morphological characterization of vinyl ester/reactive rubber systems and investigation of the mechanical and fracture behavior of these systems. Additional studies focused on rubber endcapped vinyl ester in the absence and presence of added reactive rubber. The initial compatibility of the liquid rubber with the liquid resin was studied. This is a key factor, along with cure conditions, in determination of the possible morphologies, namely, the degree of phase separation and particle size. The initial rubber/resin compatibility was found poor and all attempts to improve it by means of surfactants or ultrasonic treatment have not been successful. The flexure mechanical and fracture behavior of the cured resin/rubber systems was investigated. Three basic types of crack propagation behavior, stable, unstable, and stick‐slip, were observed. Fracture toughness of various resin/rubber systems was evaluated and was found to increase with increased content of rubbery second‐phase material. However, there is some payoff in stiffness and flexural strength of the cured resins. The addition of rubber does not affect the resin toughness at impact conditions. Analysis and interpretation of fractures morphology show that both multiple crazing and external cavitation play an important role in the fracture mechanism of the rubber modified specimens. No shear yielding is evident. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 647–657, 1999     

Creep-resistant behavior of self-reinforcing liquid crystalline epoxy resins

The creep behavior of a liquid crystalline epoxy resin (LCER) was investigated and compared with that of a non-LCER prepared from the same epoxy monomer. The experimental data was evaluated using Burgers' model to explain the reinforcing effect of the liquid crystalline (LC) phase. The long-term performance of the material was predicted using the time–temperature superposition principle. The results revealed that the introduction of an LC phase into the resin network can reduce creep strain and creep strain rate of the material, especially at elevated temperatures. Parameters extracted from the simulation indicated that instantaneous elasticity, retardant elasticity, and permanent flow resistance of the resins were enhanced by the presence of the LC phase. A rigid filler effect and a crosslinking effect are proposed to explain the reinforcing mechanisms.     

Viscosity behavior of PVC-modified liquid natural rubber blends

Compatibility of poly(vinyl chloride) (PVC) with liquid natural rubber (LNR) and epoxidized liquid natural rubber (ELNR) has been studied by solution viscometric methods. The relative viscosity versus composition plots for PVC/LNR and PVC/ELNR-20 blends are found to be nonlinear. The corresponding intrinsic viscosity values show negative deviation from ideal behavior when plotted against composition. The modified Krigbaum and Wall parameter, Δb, also shows negative values for all compositions of these blends studied. The results indicate that PVC/LNR and PVC/ELNR-20 blends are incompatible systems. On the other hand, PVC/ELNR-50 blends yielded linear plots when relative viscosity was plotted against composition. The intrinsic viscosity composition plots for this system showed positive deviation from ideal behavior. The δb values are positive for all compositions of these blends studied. These results are characteristic of a compatible blend system. Hence it is concluded that liquid natural rubber can be made compatible with PVC when the former is epoxidized to a sufficient level. © 1996 John Wiley & Sons, Inc.     

Effect of matrix ductility on the fracture behavior of rubber toughened epoxy resins

This paper investigates the effect of matrix ductility on toughness in a carboxyl-terminated butadiene-acryionitrile copolymer (CTBN) toughened diglycidyl ether of bisphenol-A (DGEBA)-piperidine system. Two kinds of epoxides were blended separately into this system to change the matrix ductility. One was a rigid and polyfunctional 4,4′-diaminodiphenol methane (MY720), and the other was a flexible diglycidyl ether of propylene glycol (DER732). The matrix T_g was significantly changed, but without alteration of the microstructure of the dispersed rubbery phase. The result of fracture energy tests reveals that the toughness of the neat epoxy resins increases slightly with the increase in the resin ductility. The toughness of the rubber-modified epoxy resins increases strongly with matrix ductility. Studies on the morphology of the toughened systems and their fracture surfaces indicate that the size of the plastic deformation zone under constant rubbery-phase morphology is determined by the multiple but localized plastic shear yielding. Increasing matrix ductility increases the size of the plastic deformation zone by inducing more extensive shear yielding. In addition, fracture surfaces reveal that as the matrix rigidity is increased, an increasing proportion of the fracture energy is dissipated by rubber cavitation during crack initiation.     

液态三元乙丙橡胶固化和力学性能的研究

液体EPDM（三元乙丙橡胶）是相对低分子量的乙烯-丙烯-共轭二烯三元共聚物,针对它的研究较少。该文主要研究了采用DCP过氧化物硫化体系硫化的液体EPDM的固化和力学性能。液体EpDM在引发剂DCP和助交联剂TAIC的作用下。凝胶含量随DCP增加无明显变化,而随TAIC增加而增大。力学性能有相似变化,不随DCP增加而改变,但随TAIC增加而增大。结果表明,交联产物的凝胶含量所表现出的其交联程度的状况导致相同的力学性能变化。实验表明,当DCP为4％、TAIC为12％时,液体EPDM的交联产物有较好的力学性能。     

An integrated experimental study of the injection molding behavior of some polyethylene resins

The present study reports on the results of an integrated experimental program to determine some of the important interactions between resin properties, moldability, and the microstructure and ultimate properties of molded articles. As part of the program, resins are characterized as to their rheological, thermal, and crystallization behavior. Then, the resins are injection molded in a laboratory machine employing simple, but highly instrumented molds in order to evaluate moldability and to produce moldings for testing and analysis. Microstructural analysis to determine morphology and orientation of the moldings is carried out utilizing polarized light microscopy and differential scanning calorimetry. Finally, shrinkage and tensile properties of the moldings are determined experimentally. To illustrate the utility of the proposed techniques, results are reported for two polyethylene resins' that exhibit superficially similar properties but, according to tests, show significant differences in moldability and product properties.     

A novel reactive liquid rubber with maleimide end groups for the toughening of unsaturated polyester resins

An amino-terminated butadiene–acrylonitrile copolymer was chemically modified into a maleim-ido-terminated rubber and was used as a toughening agent for an unsaturated polyester resin. The reactive rubber was characterized by Fourier transform infrared spectroscopy. The mechanical and fracture properties of the blends containing the unmodified and the modified rubbers were investigated. Furthermore, a morphological analysis was carried out by scanning and transmission electron microscopy. A substantial enhancement of toughness was found when the modified rubber was used in place of the plain copolymer. © 1996 John Wiley & Sons, Inc.     

Crack-growth behavior of epoxy adhesives modified with liquid rubber and cross-linked rubber particles under mode I loading

The crack-growth resistance (R-curve) of bulk single-edge notch bend (SENB) and adhesively bonded double cantilever beam (DCB) specimens was investigated under mode I loading conditions using two types of rubber-modified epoxy adhesive: one was a liquid rubber (CTBN)-modified adhesive and the other was a cross-linked rubber particle (DCS)-modified adhesive. As a result, for both the SENB and DCB specimens, the gradient of the R-curve for the DCS-modified adhesive was steeper than that for the CTBN-modified one, however, the difference in fracture toughness between DCS- and CTBN-modified adhesives is smaller for DCB than for SENB specimens. To elucidate such behavior, crack-growth simulation based on Gurson's model was conducted, where the DCS- and CTBN-modified adhesives were characterized by both the initial void fraction and nucleation. The difference in the behavior of R-curves was also observed in simulations. Moreover, it was found that the difference in fracture surface roughness observed by SEM for both adhesives correspond to the variation in R-curves.     

Synthesis and self‐healing behavior of thermoreversible epoxy resins modified with nitrile butadiene rubber

Cracks may generate in epoxy resins, which can affect the comprehensive property and shorten service life. The problem is expected to be resolved by endowing epoxy resin with self‐healing performance. Herein, a new kind of self‐healing epoxy resin containing both Diels–Alder (DA) bonds and nitrile butadiene rubber (NBR) has been developed. The self‐healing performance and mechanical properties of as‐prepared epoxy resins are investigated by qualitative observation and quantitative measuring. Results reveal that the as‐prepared epoxy resins exhibit excellent self‐healing performance and multiple repair ability, and the self‐healing behavior is based on dual actions of thermal reversibility of DA reaction and thermal movement of molecular chains. Furthermore, the thermoreversible DA bonds contribute much to the recovery of mechanical property, while the incorporated thermoplastic NBR accelerates the whole healing process. The self‐healing efficiency of epoxy resins can be enhanced markedly by introducing thermoplastic NBR. In addition, the self‐healing epoxy resins also exhibit outstanding reprocessing performance, which makes it possible of recycling waste epoxy resin. POLYM. ENG. SCI., 59:1603–1610 2019. © 2019 Society of Plastics Engineers     

Alkylated phenolic resins as antioxidants for rubber

Polymeric antioxidants based on p‐nonyl phenol formaldehyde resin (PNPF) and p‐dodecyl phenol formaldehyde resin (PDPF) were prepared by the condensation reaction of the respective phenols with formaldehyde in the presence of an acid catalyst. The reactions were monitored by thin layer chromatography, and the melting points of the products were determined. These compounds were incorporated in natural rubber mixes to evaluate their antioxidant properties. The compounded mixes were characterized for their rheometric properties. The compression‐molded rubber sheets were tested for their mechanical properties. The effects of aging on the mechanical properties of these molded sheets were evaluated. Both PNPF and PDPF showed better antioxidant properties than the conventional styreneated phenol antioxidant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2649–2651, 2006     

橡胶补强用PFM系列酚醛树脂

介绍了新型PFM系列酚醛树脂对橡胶的补强机理及在橡胶中的应用。比较了PFM系列酚醛树脂、美国Occidental公司酚醛树脂Durez1268、国内普通充油酚醛树脂SX对橡胶的增硬补强作用及对胶料加工性能的影响。结果表明,加入酚醛树脂可以使胶料获得较高的硬度和强度及较好的加工性能。酚醛树脂PFM－M和PFM－C的性能与酚醛树脂Durez12686相当,具有高补强、高增硬的特点,可在橡胶工业中推广应用。     

Viscous behavior of polymerized vegetable oils

Summary Extraction of thermally polymerized linseed oil with acetone at various temperatures yielded fractions at higher temperatures that had high molecular weights and gave intrinsic viscosity and critical miscibility plots resembling those of high polymers. Unheated oil was not an indifferent solvent for polymerized oil as judged by the temperature coefficient of intrinsic viscosity. Molecular weight information obtained with non-randomized samples suggested a linear relation between log viscosity and (Mn)1/2 for molecular weights up to 2,500. With weight average molecular weights, a linear relation between log viscosity and (Mw)1/2 obtains at molecular weights greater than 40,000. Randomization of the samples decreased their bulk viscosity while increasing polymer content. Contribution No. 374, Chemistry Division, Science Service, Ottawa. Presented, in part, at the 29th Fall Meeting, American Oil Chemists' Society, Philadelphia, Pa., October, 1955.     

Dynamic mechanical analysis of rubber toughened epoxy resins

Dynamic mechanical analysis (DMA) was used to characterize cured epoxy resin formulations from ?150°C to temperatures above their α transitions. The resins were aromatic amine and aliphatic amine cured and were modified with carboxylterminated acrylonitrile-butadiene (CTBN) rubbers to improve their toughness, A DuPont 981 dynamic mechanical analyzer was used to measure the modulus and mechanical loss factor (tan δ) of the samples. Changes in the α and β transitions in the scan of tan δ as a function of temperature were related to changes in the formulation. Relations were also sought between changes in the DMA data and fracture and impact toughness of the cured formulations obtained using an instrumented impact test. Impact tests were performed at ?196°C and at room temperature. Results indicate that fracture toughness and the dynamic mechanical properties are affected by the amount of rubber, the compatibility of the rubber and epoxy, and changes in the curing agent stoichiometry.     

Influence of liquid isoprene on rheological behavior and mechanical properties of polyisoprene rubber

Prevention of plasticizer leaching from polymers has been a difficult task. Conventional oily plasticizers (COPs) often migrate from rubber matrix, leading to a poor stability of rubber products and serious environmental problem during long‐term use. In the present study, liquid isoprene (LIP) with appropriate molecular weight and no migration was prepared by anionic polymerization. The effects of LIP on the comprehensive properties of carbon black filled polyisoprene rubber (CB/IR) composites were compared with those of one COP, naphthenic oil (NPO). The results showed that LIP reduced the Mooney viscosity and apparent viscosity, and improved the processability of CB/IR composites. LIP improved the mixing efficiency and the dispersion of the CB particles because its compatibility with CB/IR composites was higher than the compatibility of NPO and CB/IR composites. Furthermore, LIP did not migrate from the CB/IR composites because of its participation in the vulcanization reaction. Compared with CB/IR/NPO composites, CB/IR/LIP composites possessed higher mechanical properties, better aging resistance and long‐term dimensional stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41485.     

Curing behavior of Azo‐containing twin liquid crystalline epoxy resins with anhydride

A series of novel azo‐containing twin liquid crystalline (LC) epoxy monomers were cured with anhydrides without extra catalyst, and the curing kinetics was investigated by non‐isothermal differential scanning calorimetry (DSC) technique. The results showed that the effect of phase behavior on activation energy (E_a) was enormous, which increased first and then decreased quickly with the curing reaction processing. The chemical kinetic control and diffusion‐control mechanisms dominate the curing together, which gives large values of E_a. Azo group also served as a catalyst to accelerate the curing reaction. The curing mechanism was confirmed by the UV–Vis spectra of azo‐doped curing system in which the absorbance values at 366 nm and 475 nm changed with the curing reaction processing. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Microstructure,mechanical properties,and fracture behavior of liquid rubber toughened thermosets

Phenolic epoxy resin was toughened by carboxyl-randomized butadiene acrylonitrile copolymer (CRBN) for use as composite matrix. By adding different parts of butadiene acrylonitrile copolymer (BN-26, without carboxyl contained) to CRBN, different sizes of rubber domains and different numbers of chemical bondings between the resin matrix and the rubber phase were obtained. It is found that small rubber particles (less than 0.1 μm) are cavitated during the crack development. The interaction between secondary crack zones caused by the cavitation makes the fracture toughness K_IC of the materials high; by comparison, a local stress-whitened zone is produced in the material with large rubber particles (more than 0.1 μm) when it is subjected to tensile stress. In this case, the flexure strength σ_f of the material is great. Using ultrasection and TEM techniques, the stress-whitened zone was shown to be caused by the special multiple-phase structure of the material, in which many caves and “macrocrazes” coexist.     

Rheokinetical behavior of melamine-formaldehyde resins

The effects of cure temperature and amount of catalyst on the rheokinetical behavior of a melamine-formaldehyde (MF) thermosetting system is investigated using a dynamic mechanical technique similar in nature to Torsion Impregnated Cloth Analysis (TICA) and Torsional Braid Analysis (TBA). The proposed name of the used technique is Torsional Substrate Analysis (TSA). Isothermal cures of the resin are carried out from 115°C to 160°C for varying amounts of catalyst. Each TSA measurement exposes several transitions. First, a glass-to-liquid transition during the heatup procedure is seen, indicated by sharp peaks of the loss shear modulus, G″, and loss tangent, tanδ. Later, vitrification is seen, indicated by a second G″ maximum. Finally, a completion of shift to a diffusion controlled cure reaction occurs, shown as a storage shear modulus, G′, plateau. The rheokinetical data is used to construct Time-Temperature-Transformation (TTT) cure diagrams, for each level of catalyst. High pressure differential scanning calorimetry (HPDSC) measurements are carried out in order to estimate the fractional conversion of samples that have been cured isothermally for times corresponding to a second tanδ maximum, the second G″ maximum, and the G′ plateau. The fractional conversion is determined by the residual entalphy technique. The HPDSC measurements do not give a clear answer whether the second tanδ maximum corresponds to gelation or not. It is therefore likely that TSA, like similar techniques, is not capable to detect gelation. A glass transition temperature of 130°C and 150°C is found to correspond to a fractional conversion of 0.65 and ～0.80, respectively. Preliminary measurements suggest that the maximum glass transition temperature, T_{g ∞}, of the investigated MF resin is at least 180°C.     

Preparation of cardanol–formaldehyde resins from cashew nut shell liquid for the reinforcement of natural rubber

Natural rubber was reinforced with a high loading of a cardanol–formaldehyde resin prepared from cashew nut shell liquid. Cardanol–formaldehyde resins, both resoles and novolaks, were synthesized from cardanol, which was extracted from cashew nut shells. This was done by the condensation polymerization of cardanol and formaldehyde in the presence of base and acid catalysts. The cardanol–formaldehyde resole with the highest yield (ca. 75%) was prepared with a formaldehyde/cardanol molar ratio of 2.0 at pH 8.0 and 90°C for 8 h. The cardanol–formaldehyde novolak with the highest yield (ca. 80%) was prepared with a formaldehyde/cardanol molar ratio of 0.8 at pH 2.2 and 100°C for 7 h. Fourier transform infrared and ¹³C‐NMR were employed to characterize the chemical structures of the obtained cardanol–formaldehyde resins. The resins were compatible with natural rubber in various formulations. The cured behaviors of natural rubber blended with the cardanol–formaldehyde resole and novolak resins were investigated. The cured behaviors of cardanol–formaldehyde resole and cardanol–formaldehyde novolak samples were different, reflecting differences in their chemical reactivities. Furthermore, the incorporation of cardanol–formaldehyde resins into natural rubber provided significant improvements in mechanical properties such as the hardness, tensile strength, modulus at 100 and 300% elongation, and abrasion resistance. However, the elongation at break and compression set of the blends decreased as expected. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1997–2002, 2007     

The resistance of electrodeposited layers of rubber and resins

The electrical resistance per unit deposition charge per unit area (p,C^–1 cm^–2) has been calculated from current-time data for the anodic deposition of polymers in the following systems: (a) resin deposition on mild steel and copper coated mild steel, (b) rubber deposition on mild steel and aluminium, and (c) two resin systems of two concentrations on mild steel and brass. The values ofp are analyzed in detail and it is concluded thatp can be qualitatively related to the electrical conductivity of the electrode material and the adhesion of the electrodeposits, taking into consideration the different mechanism for the stability of rubber latex and the resin system. For a given value ofp, electrodeposits on aluminium are 40% more adherent than those on mild steel. Further, for the same adhesion, values ofp are lower by about 20% when aluminium is used instead of mild steel as the anode. It has also been concluded that the study ofp versus the current density during the electrodeposition of the resins is a convenient and useful method of approach to the study of electrophoresis in its practical application to the preparation of electro-coatings of industrial value.