Higher Compression Set Research Articles

Modification of hydrogenated nitrile rubber with N,N′‐bismaleimide‐4,4′‐diphenylmethane to improve its resistance to heat aging and reduce its compression set

AbstractThis paper delves to improve the upper‐limit temperature of hydrogenated nitrile rubber (HNBR) through regulation of the vulcanization process, filler system and cross‐linking additive. The tensile test and scanning electron microscope images showed that the aging at 180°C significantly accelerated the deterioration in the property of HNBR compared with 150°C aging. The results showed that a higher dosage of bis(1‐(tert‐butylperoxy)‐1‐methylethyl)‐benzene curing agent reduced the compression set of HNBR without sacrificing its tensile strength. Carbon black N539‐filled HNBR exhibited high tensile strength, while carbon black N774‐filled HNBR showed high heat resistance and low compression set. When the HNBR sample was reinforced with 20 phr of N539 and 20 phr of N774 carbon black, it achieved low compression set, high tensile strength, and heat resistance simultaneously. Then, N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) was introduced into the HNBR composite as a cross‐linking assistant agent. The residual strength of BMI‐modified HNBR was 20.3 MPa (the retention rate of 92.3%), and its compression set was as low as 19.2% after aging at 180°C for 72 h. Even after aging the composite at 180°C for 168 h, its strength retention rate remained at 83.2% (18.3 MPa). The approach provided here increased the upper‐limit temperature range of HNBR to 180°C.

A systematic study of the effect of graphene oxide and reduced graphene oxide on the thermal degradation behavior of acrylonitrile-butadiene rubber in air and nitrogen media

Thermal degradation of acrylonitrile-butadiene rubber (NBR)-graphene oxide (GO)/reduced graphene Oxide (G) composites (NBR-GO/G) was studied in air O2(g) and nitrogen N2(g) media at ∼800°C, using Thermal Gravimetric Analysis (TGA/DTG). The char yield of the composites was high the in N2(g) medium. This was associated with lower weight loss (%) and higher maximum degradation temperatures, Tmax(°C). Doyle simple kinetic approach was used for the first time to estimate the degradation kinetics of the NBR-GO/G composites and large amounts of activation energy Ea (KJ/mol) was observed, particularly for the NBR-GO composites. In O2(g) medium, severe degradation of NBR occurred irrespective of the GO/G-filler content. This suggested that insignificant char yield was produced to protect the scission of the NBR backbone, as decomposition of the main chain seemed to have been accelerated by the high oxygenated moieties (C–O–C, –O–C=O and O–H) decorating GO/G-sheets. For instance, NBR showed ∼89, ∼21 and ∼86 % weight residue, Wr (%) than G0.1, G0.5 and G1 respectively and ∼154, ∼350, ∼92 % higher than the respective GO0.1, GO0.5 and GO1 samples. Although, NBR-G recorded higher Wr(%) than NBR-GO, NBR-GO generally slowed the degradation of NBR than NBR-G composites, possibly due to the presence of high concentration of interactions (NBR—Sx—GO—S—NBR and NBR—O—Hσ+—N σ−—C—NBR) which raised the Ea (KJ/mol) barrier for decomposition. The high thermal stability and compression set (%) properties of NBR-GO/G composites obtained as compared to pure NBR indicated that solution processing techniques used in this current work was very effective than those compounded with melt mixing methods or with GO/G-functionalized nanoparticles. Therefore, this present study provides insights on tailoring rubber-graphene based materials for thermally harsh and high pressure applications such as; oil/gas drilling hose, oil/gas seals, gasket and tire tread materials.

Effects of carbon black on epoxidized natural rubber composites: Rheological, abrasion, and mechanical study

A detailed analysis of the rubber composites is necessary for the designing and fabrication of advanced rubber products. In this study, composite materials are synthesized by adding different nanofillers of carbon black nanoparticles into epoxidized natural rubber (ENR). The specific characteristics of carbon black (CB) affect the crosslinking density between CB and polymeric chains in ENR. The effects of particle size, structure, thermal conductivity, and functionality of CB on rheology and mechanical properties of filled reinforced ENR are examined. The composite materials are thoroughly characterized for their abrasion, rheology, tensile, hardness, elongation, resilience, and compression behavior. The results revealed that various properties of composite materials depend on the characteristics of the reinforcing CB fillers. It was found that lower particle size and ordered structure provide good tensile strength, tear strength, abrasion, and aging resistance. In contrast, larger particle size and a lower ordered structure provide high flow rate, low hardness, excellent re-bounce, and good compression set characteristics.

Cyclic Compression Testing of Three Elastomer Types-A Thermoplastic Vulcanizate Elastomer, a Liquid Silicone Rubber and Two Ethylene-Propylene-Diene Rubbers.

Thermoplastic elastomer vulcanizate (TPV) and liquid silicone rubber (LSR) are replacement candidates for ethylene-propylene-diene rubbers (EPDM), as they offer the possibility for two-component injection moulding. In this study, these material types were compared side by side in cyclic compression tests. The materials were also characterized to provide details on the formulations. Compared to the rubbers, the TPV had higher compression set (after a given cycle) and hysteresis loss, and a stronger Mullins effect. This is due to the thermoplastic matrix in the TPV. The LSR had lower compression set (after a given cycle) than the EPDM, but stronger Mullins effect and higher relative hysteresis loss. These differences between the LSR and the EPDM are likely due to differences in polymer network structure and type of filler. Methods for quantifying the Mullins effect are proposed, and correlations between a Mullins index and parameters such as compression set are discussed. The EPDMs showed a distinct trend in compression set, relative hysteresis loss and relaxed stress fraction vs. strain amplitude; these entities were almost independent of strain amplitude in the range 15–35%, while they increased in this range for the TPV and the LSR. The difference between the compression set values of the LSR and the EPDM decreased with increasing strain amplitude and increasing strain recovery time.

Study of the Local and Imported Rubber Products Made from Fluoroelastomer

The paper provides the results of the studies of the domestic and imported fluoroelastomer O-rings for cylinders with antifreeze cooling. It revealed that the imported materials were more efficient as they featured better compressive strain properties since they provided the acceptable sealing ability when subjected to antifreezes at elevated temperatures, as compared to the domestic materials. The different properties are explained by significantly different filler components and fluoroelastomer chemistry. The comparative analysis showed that the domestic O-rings had a higher compression set both in the coolant medium and in air. The high compression set and subsequent loss of the sealing effect can be caused by low quality of the rubber and inadequate formulation of the rubber mixture.

Viscoelastic epoxy foams by an aqueous emulsion foaming process

The research proposed an aqueous emulsion foaming process to produce a viscoelastic epoxy foam having a density of 0.33–0.36 g/cm3 from the polyamide–epoxy adduct, which uses a reverse ratio of epoxy and polyamide hardener. The process is simple, economical and uses no surfactant, thanks to the emulsifying ability of polyamide hardener. Firstly, the mixture of excess polyamide, epoxy and sodium bicarbonate was emulsified with distilled water using high-speed stirring to form dispersed epoxy droplets in water. Secondly, a solution of ammonium chloride was added, which reacted with sodium bicarbonate to produce carbon dioxide and ammonia gases dispersed in the epoxy emulsion. The expanding gases induced flocculation and partial coalescence of the epoxy droplets; sequentially water molecules were entrapped within them. Finally, a curing process was carried out to stabilise the foam morphology and structure. Two types of pore morphologies were observed: a large foam-pore generated from blowing-agent gases and a cell-wall pore formed from the vapourisation of entrapped water (as the void template). Porosity and pore morphologies depended on blowing-agent content, and the viscoelasticity was affected by the epoxy/polyamide ratio. The obtained viscoelastic foams showed a large number of interconnected cells and exhibited high compression set values.

Preparation of natural rubber elastomeric bridge bearing pad compound formula on various curing systems

Commercial elastomeric bridge bearing (EBB) pad is dominated by the laminated type. Laminated EBB pad comprises of rubber composite layers which are arranged intermittently among the thin steel plates. The rubber composite uses natural rubber or chloroprene synthetic rubber as the base elastomer. Local EBB pad industries mostly produce natural rubber bridge bearing pad type due to the enormous availability of natural rubber in Indonesia. However, the quality of natural rubber bridge bearing pad product often cannot fulfil the standard requirement in compression set and accelerated aging parameters. The research studied the design of EBB pad compound formula based on natural rubber type. The EBB compound formulas were prepared by varring the curing system such as sulphur (efficient and semi-efficient) and peroxide curing system. Designing the compound formula was in accordance to the methods required in improving the compression set and accelerating aging quality of natural rubber bridge bearing pad. The result of curing characteristic of the natural rubber bridge bearing pad compound showed that peroxide curing system gave the longest optimum curing time. Further, sulphur curing system produced high crosslink density followed with good mechanical properties of natural rubber bridge bearing pad vulcanizate. The compression set value of natural rubber bridge bearing pad vulcanizates which were obtained by efficient and semi-efficient curing systems as 14.09% and 24.81%, respectively were regarded to be below the maximum requirement (25%). The peroxide curing system was not recommended due to the high compression set value of 40.68%. Meanwhile, maximum percent changes of tensile properties and retention values which indicated accelerated aging parameter of natural rubber bridge bearing pads were formed either by sulphur and peroxide curing system could fulfilled the standard requirement of EBB Duro 70 refered to SNI 3967:2013.

Optimization of the Thermo-Hygromechanical (THM) Process for Sugar Maple Wood Densification

Densified wood is a promising engineered wood product, especially for heavy-duty applications. This study optimized the temperature and duration of the thermo-hygromechanical (THM) densification process applied to sugar maple (Acer saccharum Marsh.) wood. The response variables studied were compression set recovery and hardness. The THM densification process was performed at three temperatures (180°C, 200 °C, and 220 °C), densification times (450 s, 900 s, and 1350 s), and post-treatment times (900 s, 1350 s, and 1800 s). Response surface methodology was used to analyze the impact of the three parameters. The effect of temperature on the density profile across thickness was also determined. The results suggested that the optimum densification conditions resulting in high hardness and low compression set recovery were obtained at a temperature of 180 °C, a densification time of 1004 s, and a post-treatment time of 1445 s. Additionally, the density of the densified samples was relatively homogeneous across thickness, although it was dramatically increased compared with control samples. However, density did not increase linearly with temperature. A much higher weight loss occurred at 220 °C, resulting in a significant decrease in density and hardness, whereas little compression set recovery was observed for sugar maple densified at this temperature.

Preparation and properties of bio-based polyurethane foams from natural rubber and polycaprolactone diol

Bio-based polyurethane foam (PUF) was synthesized by a one-shot polymerization using hydroxyl telechelic natural rubber (HTNR) and polycaprolactone (PCL) diols as a soft segment. The effect of HTNR/PCL diol molar ratio (1/0, 1/0.5, 1/1 and 0.5/1) on the foam formation rate and physical and mechanical properties of the resulting PUF was investigated. The formation of urethane linkage and cross-linked structure were confirmed by FTIR analysis. The foams observed by scanning electron microscope revealed to have almost closed cells. The molar ratio of HTNR/PCL diol affected the foam formation rate, the average diameter of cell, the regularity of cell shape, the elongation at break and the compressive strength. The foam density slightly changed with this molar ratio whereas the specific tensile strength of all samples was in the same range. All PUFs showed relatively high compression set. The biodegradability was assessed according to a modified Sturm test. Low density polyethylene and sodium benzoate were used as a negative and positive control sample, respectively. PUF samples showed an induction time of 33 days in which the percentage of biodegradation was ~7–11 %. At the end of testing (60 days), the highest degradation (45.6 %) was found in the sample containing 1/0.5 of HTNR/PCL diol molar ratio.

Dimensional stability, fungal resistance and mechanical properties of radiata pine after combined thermo-mechanical compression and oil heat-treatment

Abstract The dimensional stability and mechanical properties of radiata pine (Pinus radiata) has been investigated after thermo-mechanically compression (TMC) followed by oil heat-treatment (OHT). Wood specimens were first compressed in the radial direction then heat-treated in a linseed oil bath at 160–210°C. Spring-back percentage, water repellence efficiencies, and compression set recovery percentage were determined as indicators of dimensional stability. The resistance of treated wood against a brown rot fungi was assessed based on an accelerated laboratory fungal decay test. Strength, stiffness and hardness were determined as a function of different treatment parameters. After TMC, high compression set (39%) was achieved without any surface checks and cracks. Specimens undergoing TMC followed by OHT showed relatively less swelling and low compression set recovery under high moisture conditions. The fungal resistance of wood after TMC+OHT slightly increased compared to untreated wood and TMC wood. The mechanical properties of TMC+OHT wood were inferior to those of TMC wood.

Kinetics of Peroxide Vulcanization of Natural Rubber

This study was undertaken to optimize the vulcanization conditions and explore the effect of residual peroxide in the peroxide vulcanization of natural rubber. The study was followed through the kinetics of the vulcanization reaction at various temperatures viz. 150,155,160 and 165°C. Dicumyl peroxide (DCP) was used as the crosslinking agent. The Monsanto Rheometer was used to investigate the different crosslinking stages and vulcanization kinetics. The thermal decomposition of peroxide followed a first order free radical decomposition reaction. Half-lives at various temperatures were determined. The percentage of residual peroxide was calculated from the cure kinetic data. The effect of residual peroxide on mechanical properties was studied at various peroxide levels and also by extending the cure time (from t90 to t95 and then to t100). Mechanical properties such as tensile strength, elongation at break, modulus and compression set (70 and 100°C) were measured. Excess peroxide was found to cause a high compression set at elevated temperature and the cure time was selected to achieve minimum residual peroxide in the product. Results indicate that peroxide concentration is the dominant factor controlling the crosslink density and hence the properties of the vulcanizates.

Densification of wood veneers by compression combined with heat and steam

Wood veneer 700×700 mm2 specimens made with aspen (Populus tremuloides) and hybrid poplar clone 15303 (Populus maximowiczii × Populus balsamifera) were densified using heat, steam, and pressure. Temperatures of 140, 160, 180, 200, and 220°C were applied at a maximum steam pressure of 550 kPa and maximum press hydraulic pressure ranging from 4.5 to 9.0 MPa. After densification, the oven-dry density increased significantly, veneers darkened, and lathe checks that were present on veneers before densification were conglutinated and veneer surface roughness decreased. Densified veneers showed markedly reduced hygroscopicity: the higher the densification temperature, the lower the wood hygroscopicity. The Brinell hardness of densified veneer was about two to three times that of control for both aspen and hybrid poplar. Tensile and bending strength also increased significantly after densification. However, the mechanical properties of densified veneers decreased slightly with increased densification temperature. The modulus of elasticity in tension and bending increased after densification, especially at high temperatures. A very high compression set recovery was found for veneers densified at low temperatures. Recovery decreased dramatically when densification temperature exceeded 180°C. Almost no recovery was found for veneers densified at 220°C.

Characterization of local deformation in filled-silicone elastomers subject to high strain – NMR MOUSE and Magnetic Resonance Imaging as a diagnostic tool for detection of inhomogeneities

Magnetic Resonance Imaging (MRI) and unilateral Nuclear Magnetic Resonance (NMR) relaxometry with the NMR MOUSE (MObile Universal Surface Explorer) have been used to characterize local permanent deformation in silicone parts subject to high compressive strain. Samples returned from field service have been characterized by areas of high compression set. Materials excised from these damaged sections have been shown to be clearly distinguishable from undeformed material from the same part and from pristine material by NMR spin-echo, NMR MOUSE and MRI protocols. The results of these studies have been interpreted in the context of studies of model materials of varying crosslink density. The areas of local deformation have been characterized by a reduction in the residual dipolar coupling, which is proportional to the crosslink density and in the non-network sol fraction. These differences were likely to be present in these polymers at the time of production due to inefficient mixing. Additionally, both T 2 weighted Single Point Imaging (SPI) and T 2 weighted MRI experiments have been used to map out the location of different crosslink densities, ultimately determining the quality or homogeneity in silicone components.

WHITE RICE HUSK ASH FILLED ETHYLENE-PROPYLENE-DIENE TERPOLYMER/POLYPROPYLENE BLENDS: EFFECT OF DYNAMIC VULCANIZATION AND FILLER LOADING

The effect of dynamic vulcanization and influence of filler loading of white rice husk ash filled elastomer rich ethylenepropylene diene terpolymer and propylene blends were investigated. Blends with filler loading ranging from 0 to 60 php (Parts per hundred of total polymer by weight) were prepared in a Brabender plasticorder at 180°C and a rotor speed of 50 rpm followed by compression molding. The Brabender torque was used to investigate mixing progress. The mechanical properties of vulcanized blend systems were compared with those of the unvulcanized counterparts. The mechanical properties of the blends as a function of filler loading were also studied for both blend systems. Processability and recyclability of the blends were carried out to assess the thermoplastic characteristics of the blends. Brabender torque studies showed that dynamic vulcanization has a more significant effect on melt rheology than filler loading. It was also found that unvulcanized blends exhibited poor tensile properties, low hardness and high compression set. However, dynamically vulcanized blends exhibit mechanical properties, which are superior to those of unvulcanized blends. As filler loading increases, the hardness of the blends slightly increases whereas tensile properties, tear strength, and compression set deteriorates. Processability and the possibility of recycling of dynamically vulcanized blends with high elongation and low compression set indicate that dynamic vulcanization confers thermoplastic elastomeric properties to the blends. The study further revealed that white rice husk ash filled blends can also be dynamically vulcanized to achieve enhanced properties in a similar manner to the unfilled blends.

Effects of various acid acceptors upon stress relaxation and set in epichlorohydrin elastomers

Epichlorohydrin (ECO) elastomers are used as seals and gaskets. Therefore, it is desirable to minimise compression stress relaxation and compression set. These properties are strongly influenced by the extent and nature of crosslinks. Compounding ingredients that interfere with crosslinking will profoundly affect stress relaxation and set. Acid acceptors are essential for ECO elastomers because they impart heat stability and neutralise hydrochloric acid. The present paper describes and discusses the way in which various acid acceptors affect compression stress relaxation and set in ECO elastomers. Lead based and non-lead based acid acceptors were studied. The lead based acid acceptors were litharge, red lead, and dibasic lead phosphite–dibasic lead phthalate. The non-lead based types comprised zinc oxide, magnesium oxide, and calcium oxide. Results appear to indicate that at similar crosslink concentrations, ECO vulcanisates containing lead based acid acceptors give lower rates of compression stress relaxation and lower set at ambient temperatures than do the non-lead based acid acceptors. This feature may be due to the variable stiffening action of the various metal chlorides that are produced during vulcanisation. As regards high temperature compression set, the lead based acid acceptors gave lower set values than did the non-lead based counterparts. The high temperature compression set of ECO containing zinc oxide was extremely high, probably because oxide becomes a strong Lewis acid and thus rapidly promotes elastomer breakdown.

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4?-diisocyanatodicyclohexyl methane

The physical and thermal properties of hand-cast polyurethane and polyurethane/polyurea elastomers prepared from prepolymers of 20 and 97% trans,trans-4,4′-diisocyanatodicyclohexyl methane (t,t-rMDI) and C3- and C4-polyethers chain extended with either 1,4-butanediol (XB) or a commercial mixture of diethyl toluenediamine isomers (DETDA) were determined. The influence of the distribution of geometric isomers of the diisocyanate and of the chain-extender building blocks on these properties is significant. Urethane/ureas are harder and have higher modulus than polyurethanes formed from the same prepolymer. The polyurethane/polyurea elastomers all have somewhat high compression set. Dynamic Mechanical Analysis (DMA) suggests that DETDA extended systems based on 20% t,t-rMDI are phase separated, as illustrated by extended rubbery plateau regions and significantly higher softening points than the corresponding XB extended ones. Uniquely, these elastomers are transparent rather than opaque as typical with most other phase-segregated elastomers. Polyurethanes based on 97% t,t-rMDI are harder and have higher modulus than those based on 20% t,t-rMDI (Desmodur™ W). They have good phase separation and high softening points but they are opaque. Surprisingly, there is not much difference between the physical or thermal properties of polyurethane/polyureas and polyurethanes based on 97% t,t-rMDI. Replacing XB with DETDA gives only moderate improvement in properties, but it does make the elastomers optically clear. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 957–970, 1997

Movement capability of sealants

The paper describes experimental work carried out in support of the development of an International Standard on sealant durability. It compares the results of different lab tests, suggested during the development of the Standard, with those obtained from outdoor weathering under mechanical strain. The comparison shows that the 70°C compression test, as included in ASTM C-719, is helpful in identifying sealants which fail due to high compression set. The heat compression test, however, does not rule out sealants that tend to post-cure or embrittle upon ageing. The best correlation between lab tests and outdoor weathering is obtained if the sealants are allowed to cure fully prior to lab testing.

Self-vulcanizable ternary rubber blend based on epoxidized natural rubber, carboxylated nitrile rubber and polychloro-prene rubber: 2. Effect of blend ratio and fillers on properties

Mill-mixed blends of epoxidized natural rubber (ENR), carboxylated nitrile rubber (XNBR) and neoprene form a self-vulcanizable ternary blend system which can be reinforced by fillers such as carbon black and silica. The effect of fillers on processing characteristics and physical properties of self-vulcanizable blends is similar to that of conventional rubbers. The properties depend on blend ratio and type of filler. The blend in the gum state shows poor failure properties like gum ENR, but shows high resilience and low compression set. Abrasion loss and heat build-up properties of the blend are nearer to those of gum neoprene vulcanizate. The filled blends show lower heat build-up due to non-uniform distribution of fillers in the miscible ternary blend. Mooney viscosity and Mooney scorch time of the blend are found to be intermediate between the control mixes of ENR and XNBR, but the Monsanto rheometric torque values are closer to ENR.

Effect of curing temperature and curing system on network structure and technical properties of polybutadiene and styrene–butadiene rubber

The effect of curing temperature and curing system on the network structure and technical properties of polybutadiene (BR) and styrene–butadiene rubber (SBR) has been studied. The technical properties have been correlated with the network structure. For example, better dynamic properties like resilience, heat buildup, and set values of the efficiently vulcanized BR system can be ascribed to lower sulfur inefficiency and simpler network structure. Again, higher compression set values of the SBR mixes are due to lower crosslink density and higher proportion of polysulfidic crosslinks.

Effect of vulcanization temperature and synergism of accelerators on the network and technical properties of efficiently vulcanized natural rubber mixes

The effect of an increase in vulcanization temperature from 150° to 180°C on the network structure and technical properties of gum natural rubber vulcanizates has been studied using six different binary combinations of tetramethyl thiuram disulphide (TMTD) and 2-(morpholinodithio)benzothiazole (MDB) at fixed sulphur level (0.6 parts per hundred rubber). On the basis of processing safety, reversion resistance, technical properties, retention of properties after aging and percentage losses in properties on increasing the vulcanization temperature by 30°C, if was found that the combination with MDB (1.2 phr) TMTD (0.6 phr) showed the best synergism of the two accelerators. Results of chemical characterization of vulcanizate networks have been correlated with their technical properties. At higher vulcanization temperature, lower degree of crosslink density and with increasing extent of sulphidic main chain modification, a reduction in strength, modulus, hardness and resilience resulted and brought about a higher compression set and a greater heat build-up during Goodrich flexometer tests. The better cut growth and flex properties of vulcanizates cured at 180°C have been explained on the basis of the distribution of different types of crosslinks and stress relaxation caused by lower crosslink density.