Mechanical, thermal and transport properties of nitrile rubber (NBR)—nanoclay composites

The article describes the properties of nitrile rubber (NBR)—nanoclay composites prepared by a two-step method. viz. preparation of a 3:1 [by weight] masterbatch of NBR and nanoclay followed by compounding on a two roll mill and molding at 150 °C and 20 MPa pressure. The tensile strength, elongation at break, modulus, storage modulus (E’) and loss modulus (E”) increased with the nanofiller content, reached the maximum value at 5 phr and decreased thereafter. The solvent uptake, diffusion, sorption and permeation constants decreased with nanoclay content with the minimum value at 5 phr nanoclay. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. supported by morphological analysis.     

Mechanical,morphological and thermal properties of short carbon and aramid fibres-filled bromo-isobutylene-isoprene rubber vulcanised with 4, 4’ bis(maleimido)diphenylmethane

ABSTRACT

This paper describes the use of a combination of 4, 4’ bis(maleimido)diphenylmethane and ZnO as a high-temperature processable vulcanising agent for the short aramid and carbon fibre-filled bromo-isobutylene-isoprene rubber. The fibre breakage analysis, cure characteristics, mechanical, thermal and morphological properties of the composites were evaluated with different fibre loading. The fibre breakage analyses revealed that the aramid fibres have good length retention property compared to carbon fibres. The morphological analysis of the extracted aramid fibres showed severe surface roughness primarily due to fibrillation after shear mixing. The fibrillated aramid fibres lead to aggregation and poor dispersion of the fibres in the rubber matrix. However, fibrillation imparted surface roughness and increased surface area on the aramid fibres which improved the fibre–matrix interaction via mechanical anchoring. On the other hand, the carbon fibre-filled composite showed poor fibre–matrix interaction and inferior strength and modulus.     

The structure and dynamic properties of nitrile–butadiene rubber/poly(vinyl chloride)/hindered phenol crosslinked composites

In this article, a new nitrile–butadiene rubber (NBR) crosslinked composites containing poly(viny chloride) (PVC) and hindered phenol (AO-80 and AO-60) was successfully prepared by melt-blending procedure. Microstruture and dynamic mechanical properties of the composites were investigated using SEM, DSC, XRD, and DMTA. Most of hindered phenol was dissolved in the NBR/PVC matrix and formed a much fine dispersion. The results of DSC and DMTA showed that strong intermolecular interaction was formed between the hindered phenol and NBR/PVC matrix. The NBR/PVC/AO-80 crosslinked composites showed only one transition with higher glass transition temperature and higher tan δ value than the neat matrix, whereas for the NBR/PVC/AO-60 crosslinked composites, a new transition appeared above the glass transition temperature of matrix, which was associated with the intermolecular interaction between AO-60 and PVC component of the matrix. Both AO-80 and AO-60 in the crosslinked composites existed in amorphous form. Furthermore, the chemical crosslinking of composites resulted in better properties of the materials, e.g., considerable tensile strength and applied elastic reversion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physical–mechanical properties of carbon black–nanoclay composites of butyl rubber as curing bladder compounds

Abstract

Partial replacement of carbon black (CB) by organically modified montmorillonite (OMMT) in bladder compounds and synergistic effect between OMMT and CB on required properties were studied. X-ray diffraction results revealed intercalation of rubber into OMMT galleries. Mechanical interaction between rubber and filler, mechanical stability in oxidative aging, resistance to permanent set, reduction in permeation to CO₂, and resistance to thermal degradation were all in favour of clay containing composites, especially the compound with 45?phr CB and 4?phr OMMT.     

Stress–thermal oxidative aging behavior of hydrogenated nitrile rubber seals

The long-term thermal oxidative aging behavior of uncompressed and compressed hydrogenated nitrile rubber seals was studied in terms of the weight loss, chemical structure, crosslinking density, compression set, fracture morphology, and mechanical properties. It was found that weight loss of the uncompressed seals was more than that of the compressed seals due to restricted mobility of additives and molecular chains under compression. The ATR–FTIR results showed that hydroxyl groups and carbonyl groups both were formed under the uncompressed and compressed states, whereas only the generation of amide groups was observed under the uncompressed state. Additionally, crosslinking reactions dominated throughout the aging process, but stress-induced and oxidation-induced chain scissions occurred and competed with crosslinking during subsequent middle and later stages of aging at 110 °C. Compression set of the compressed seals implied the formation of a denser network structure. The surface damage of the uncompressed seals gradually turned more serious and inhomogeneous than that of the compressed seals. Mechanical properties of the uncompressed and compressed seals showed a similar variation tendency with exposure time and degraded more seriously at higher temperatures. The TGA results indicated that the aging conditions (elevated temperature and compressive stress) did not significantly affect the thermal stability of the rubber seals. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47014.     

Bond characteristics,mechanical properties,and high-temperature thermal conductivity of (Hf1−xTax)C composites

Bond characteristics, mechanical properties, and high-temperature thermal conductivity of ultrahigh-temperature ceramics (UHTCs), hafnium carbide (HfC), tantalum carbide (TaC), and their solid solution composites, were investigated using first-principles calculations. Mulliken analyses revealed that Ta formed stronger covalent bonds with C than did Hf. Bond overlap analyses indicated that the Hf–C bond possessed mixed covalent and ionic bond characteristics, compared with the more covalent character of the Ta–C bond. Consequently, the overall elastic properties were enhanced with increasing number of Ta–C bonds in the composites. The overall metallicity of the composites also increased with increasing TaC content; thus, the mechanical properties did not improve monotonically. Our results indicate that adding a small amount of TaC to HfC or vice versa to produce a composite would create a new UHTC with greatly improved elastic and mechanical properties as well as high-temperature thermal conductivity.     

Mechanical and thermal properties of hybrid carbon fibre–phenolic matrix composites containing graphene nanoplatelets and graphite powder

Carbon fibre–phenolic matrix (CF–P) composites containing graphene nanoplatelets (GNPs) were manufactured for improved mechanical and thermal properties. For comparison, micrometer-size pyrolytic graphite powder (GP) was also incorporated in CF–P composites. The loading of carbon fibres was kept constant at 60?wt-% while the quantity of GNPs was varied from 0.1?wt-% to 0.3?wt-% and GP from 1.0?wt-% to 3.0?wt-%. Only GNPs were functionalised by ultraviolet-ozone treatment to improve their dispersion in the matrix while all the composites were manufactured by hand layup method and characterised by scanning electron microscopy, impact, flexural, thermogravimetry and ablation tests. The composite containing 0.3?wt-% GNPs showed considerable improvement in ablation, flexural and impact testing as compared to CF-P composites containing GP. Finally, the ablation mechanisms of post-ablated composites were discussed in the light of available data in the literature.     

Microstructure,mechanical properties and thermal conductivity of (Ti0.5Nb0.5)C–SiC composites

A series of (Ti_0.5Nb_0.5)C-x wt.% SiC (x = 0, 5, 10, 20) composites were prepared by spark plasma sintering. Dense microstructures with well‐dispersed SiC particles were obtained for all composites. With the increment of SiC content, the Vickers hardness, Young's modulus and fracture toughness increase monotonically. An optimized flexural strength of 706 MPa was achieved in (Ti_0.5Nb_0.5)C-5 wt.%SiC composite. (Ti_0.5Nb_0.5)C-20 wt%SiC composite exhibits the highest fracture toughness of 6.8 MPa m^1/2. The crack deflections and the suppression of grain growth were the main strengthening and toughening mechanisms. Besides, (Ti_0.5Nb_0.5)C-20 wt%SiC composite exhibit the highest thermal conductivity of 45 W/m·K at 800 °C.     

Preparation, characterization and thermal properties of organic–inorganic composites involving epoxy and polyhedral oligomeric silsesquioxane (POSS)

Organic–inorganic hybrids comprising epoxy resin and polyhedral oligomeric silsesquioxanes (POSSs) were prepared via in situ polymerization of the diglycidyl ether of bisphenol A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM). The POSSs have an active functional group that takes part in the ring-opening reaction with the oxirane group. The organic and inorganic moieties are joined by covalent bonds. These covalent bonds enhance the compatibility of the inorganic and organic phases. Scanning electron microscope (SEM) analytical results indicate that there was no obvious phase separation between the inorganic and organic phases. The UV/VIS spectrum of the epoxy hybrid demonstrates the excellent optical transparency of the hybrids—the most important characteristic for their application as protective coatings. Thermogravimetric analysis (TGA), X-ray photoelectron spectra (XPS), and nuclear magnetic resonance spectroscopy (NMR) of the char showed that the incorporation of the POSSs into epoxy resin improves the thermal stability of the hybrids.     

Mechanical properties of silicon carbide—in situ zirconium carbonitride composites

SiC–Zr₂CN composites were fabricated by conventional hot pressing from β-SiC and ZrN powders with 2 vol% equimolar Y₂O₃–Sc₂O₃ as a sintering additive. The effects of the ZrN addition on the room-temperature (RT) mechanical properties and high-temperature flexural strength of the SiC–Zr₂CN composites were investigated. The fracture toughness gradually increased from 4.2 ± 0.3 MPa·m^1/2 for monolithic SiC to 6.3 ± 0.2 MPa·m^1/2 for a SiC–20 vol% ZrN composite, whereas the RT flexural strength (546 ± 32 MPa for the monolithic SiC) reached its maximum of 644 ± 87 MPa for the SiC–10 vol% ZrN composite. The monolithic SiC had improved strength at 1200°C, whereas the SiC–Zr₂CN composites could not retain their RT strengths at 1200°C. The typical flexural strength values of the SiC–0, 10, and 20 vol% ZrN composites at 1200°C were 650 ± 53, 448 ± 31, and 386 ± 19 MPa, whereas their RT strength values were 546 ± 32, 644 ± 87, and 528 ± 117 MPa, respectively.     

Mechanical properties of functionally graded carbon black–styrene butadiene rubber composites: Effect of modifying gradation and average filler loading

The mechanical properties of functionally graded polymeric composites (FGPCs) with varying carbon black loading and the effect of stacking sequence in styrene butadiene rubber (SBR) matrix were studied. For a given average amount of nanofiller, the modulus of FGPCs for any given stacking sequence of layers is higher when compared with its uniformly dispersed polymeric composites (UDPCs) counterpart. Tensile strength, elongation at break, and tear strength either increase or decrease depending on the stacking sequence and average loading of the filler in FGPCs. In addition, the smoother gradation (i.e., lesser difference in the amounts of CB content in adjacent layers) and a wide gap of difference in CB content in a stack has a profound effect on the modulus and tensile strength of FGPCs. Dynamic mechanical analysis shows lesser damping in FGPCs than UDPCs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical and thermal properties of copoly(styrene/acrylonitrile) compatibilised Nylon–thermoplastic elastomer blends

Abstract

The effects of blend compositions on the mechanical and thermal properties of polymer blends containing Nylon 66 and a thermoplastic elastomer (TPE), Santoprene^®, have been studied. A 5% styrene/acrylonitrile copolymer was added to neat Nylon, TPE, and their blends. The blends were injection moulded and the tensile and impact properties were investigated. The morphology and thermal properties of the blends were observed using scanning electron microscopy and differential scanning calorimetry.

The presence of double melting temperatures showed that the Nylon 66 and TPE are immiscible. However, blending produced a modification of mechanical and thermal properties. At TPE/Nylon ratios above 50 : 50 the tensile properties of TPE improved. In addition the impact properties of Nylon improved above the 50 : 50 ratio, i.e. in the TPE rich region. Both the melting temperature and crystallinity were depressed in the region of 50 : 50 blend composition. The presence of two phases, which is evidence of immiscibility of the blends, was confirmed by scanning electron microscopy.     

Mechanical and thermal shock properties of size graded MgO–PSZ refractory

The effects of the mixture of coarse powder with fine PSZ powder on the thermal-mechanical properties of 10 Mg–PSZ samples were studied. The size graded specimens were injection-molded using 3.5 m% MgO–ZrO₂ powders. The physical properties of the ZrO₂ samples and five thermal shock parameters were measured and calculated. These properties included density (ρ), porosity (p), the ratio of m/(t+c+m) phase, fracture toughness (K_IC), strength (σ_f), Young's modulus (E), shear modulus (G), Poisson's ratio (ν), and the thermal expansion (α) between ambient temperature to 1100°C. The toughness and thermal shock resistance of the PSZ are controlled by the states of porous microstructure which can be represented by a parameter (nominal largest tolerable length of defects) a_t. The PSZ samples show two types of thermal shock behavior differentiated by comparing the value of a_t to the characteristic length L_f of the defects in the sintered PSZ. The states of the defects, i.e. porosity, are the microstructural evidence to explain the relationship between the thermal shock properties.     

Enzymatic degradation,electronic, and thermal properties of graphite- and graphene oxide-filled biodegradable polylactide/poly(ε-caprolactone) blend composites

Commodity polymers are the most widely used materials for electronic packaging applications. However, they are nondegradable and causing serious environmental damage. Addressing this challenge, the relative effects of graphite (G) and graphene oxide (GO) dispersion on the enzymatic degradation, electronic properties, thermal degradation, and crystallization behavior of enzyme degradable polylactide/poly(ε-caprolactone) blend composites is investigated. Owing to the oxygenated surface functionalities and excellent thermal conductivity arising from the carbon structure, the randomly dispersed GO particles do not provide electrical pathways and facilitate large enhancements in the electrical resistivity (126%) and thermal conductivity (72%) of the blend composites. However, while the G particles enhanced the thermal conductivity of the composites, they had little effect on enzymatic degradation. Furthermore, they reduced the electrical resistivity, particularly at high concentration (0.25 wt % G), as a result of the conducting delocalized electrons in the G structure and due to network formation. We also find that the energy required to initiate and propagate the thermal degradation process for GO-filled blend composites is relatively lower than that of G-filled blend composite. However, the former composites show higher crystallization rate coefficients value than that of G-filled composites and the neat blend, thereby providing better crystallization ability and miscibility with the matrix. In summary, the GO-filled blend composites are observed to show potential for use in sustainable materials for thermal management applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47387.     

PBAT/hybrid nanofillers composites—Part 2: Morphological,thermal and rheological properties

This work is an investigation of the effect of different nanofillers: organically modified montmorillonite (MMT), sepiolite (SEP) and nano titanium dioxide (nTiO₂) and combination of them in poly(butylene adipate-co-terephthalate) (PBAT) films. Thermal morphological and rheological analyses were conducted to explain the behavior of this nanoparticles on O₂ and water vapor permeability coefficients, light transmission, and mechanical properties presented in previous study. Thermal stability of the nanocomposites was slightly decreased by the nanofillers presence. Differential scanning calorimetry and X-ray analyses were carried out to investigate the crystallization behavior of nanocomposites. Transmission electron microscopic analysis showed regular and homogeneous dispersion of the nanoparticles, but scanning electron microscopy showed lack of adhesion in the sepiolite-PBAT interface. Rheological measurements showed significant increase in both complex viscosity and storage modulus due to interactions between clays and PBAT and the effect of sepiolite and nTiO₂ on improving the exfoliation of montmorillonite as synergism between the nanofillers.     

Thermorheological studies of novel thermoplastic elastomeric blends of nitrile rubber (NBR) and scrap computer plastics (SCP) based on acrylonitrile–butadiene–styrene terpolymer (ABS)

Abstract

Thermorheological properties of thermoplastic elastomeric 60/40, 70/30 and 80/20 nitrile rubber (NBR)/scrap computer plastics (SCP) blends were studied by using parallel plate rheometer. The blends exhibit pseudoplasticity and obey power law model. The dynamically vulcanised blends have higher dynamic viscosities than their unvulcanised counterparts. Surface finish and die swell of the extrudates are improved upon dynamic vulcanisation. The thermoplastic elastomeric blends of NBR/SCP exhibit 'thermorheological complexity'.     

Morphological characteristics and thermal,rheological, and mechanical properties of cellulose nanocrystals-containing biodegradable poly(lactic acid)/poly(ε-caprolactone) blend composites

This work investigates the effect of cellulose nanocrystal (CN) loading on the properties of polylactide / poly(ε-caprolactone) (PLA/PCL) (70/30) blend processed in a twin-screw extruder as a potential material that can be utilized in various applications where biodegradation is highly desired. The morphological analysis revealed a reduction in droplet size of dispersed PCL phase upon addition of CN at low concentrations (1 and 2 wt %) with maximum reduction at 2 wt % which led to maximum improvement in mechanical properties. The reinforcing effect of CN in increasing the DMA storage modulus of the prepared systems was noticed when CN concentration was increased. Further, CN enhanced the crystallization of PCL, whereas the cold crystallization of PLA remained the same with CN addition. Both melt strength and viscosity of PLA improved with the incorporation of PCL and CN. In general, a green composite material with improved properties was successfully prepared using an environmentally friendly filler material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48665.     

Mechanical and thermal properties of δ-RE4Hf3O12 (RE = Yb,Lu)

Rare-earth (RE) hafnates are promising thermal and environmental barrier coating (TEBC) materials for SiC_f/SiC ceramic matrix composites. In this study, pure-phase and dense δ-RE₄Hf₃O₁₂ (RE = Yb, Lu) bulk ceramics have been fabricated via a hot-pressing method. The crystal structure, microstructure, mechanical, and thermal properties of δ-RE₄Hf₃O₁₂ were systematically investigated in order to probe their potential application as TEBCs. The high-temperature elastic moduli of δ-Yb₄Hf₃O₁₂ and δ-Lu₄Hf₃O₁₂ are measured to be 185 and 188 GPa at 1673 K, respectively, which are over 85% values of room temperature. The coefficients of thermal expansion are 7.64 × 10⁻⁶ and 7.46 × 10⁻⁶ K⁻¹ for δ-Yb₄Hf₃O₁₂ and δ-Lu₄Hf₃O₁₂, respectively. The relatively low coefficient of thermal expansion and thermal conductivity as well as their excellent high-temperature stability endow these hafnates as potential TEBC candidates.     

Effects of vinyltrimethoxy silane on thermal properties and dynamic mechanical properties of polypropylene–wood flour composites

The viability of vinyltrimethoxy silane was investigated as a coupling agent for the manufacture of wood–plastic composites (WPC). The effect of silane pretreatment of the wood flour on the thermal and the dynamic mechanical properties and thermal degradation properties of the composites were studied. Moreover, the effect of organosilane on the properties of composites was compared with the effect of maleated polypropylene (MAPP). DSC studies indicated that the wood flour acts as a PP-nucleating agent, increasing the PP crystallization rate. In general, pretreatment with small amounts of silane improved this behavior in all the WPCs studied. Thermal degradation studies of the WPCs indicated that the presence of wood flour delayed degradation of the PP. Silane pretreatment of the wood flour augmented this effect, though without significantly affecting cellulose degradation. Studies of dynamic mechanical properties revealed that the wood flour (at up to 30 wt %) increased storage modulus values with respect to those of pure PP; in WPCs with a higher wood flour amount, there was no additional increase in storage modulus. Pretreatment of the wood flour with silane basically had no effect on the dynamic mechanical properties of the WPC. These results show that with small amounts of vinyltrimethoxy silane similar properties to the MAPP are reached. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of polymeric plasticizer from PET waste and its applications in nitrile rubber and nitrile–PVC blend

Polyethylene terephthalate (PET) waste is not biodegradable; thus, it will create environmental hazards if disposed in landfills. Therefore, the only way of addressing the problem of disposal of post-industrial and post-consumer PET wastes is through recycling. The polyester plasticizer for polyacrylonitrile butadiene rubber (NBR) and polyacrylonitrile butadiene–polyvinylchloride rubber blend (NBR–PVC) was obtained by the depolymerization of PET waste with 2-ethyl-1-hexanol. The PET waste was depolymerized until a polymeric plasticizer with the average molecular weight in the range of 450–900 g/mol was obtained. The polymeric plasticizer was characterized for acid and hydroxyl numbers, viscosity, density, FTIR, NMR and TGA/DTA thermogram. The prepared polymeric plasticizer was used in the preparation of nitrile rubber and nitrile–PVC rubber blend rubber sheets, where these sheets were tested for compatibility, tensile strength, elongation-at-break, hardness and ageing properties. Nitrile rubber and nitrile–PVC blend sheets were also prepared using DOP as a plasticizer and a comparative study with the synthesized polymeric plasticizer was made. It was observed that synthesized polymeric plasticizer provides excellent tensile properties and ageing resistance for high-performance applications as compared to that obtained from DOP. The end uses for nitrile rubber and nitrile–PVC rubber blend compounds are quite diverse, but they can be loosely categorized as being either general performances or higher performance applications. Each of these performance categories requires a different set of considerations in terms of compounding with plasticizers.