Zonglin Peng

Influence of clay modification on the structure and mechanical properties of EPDM/montmorillonite nanocomposites

Abstract Conditions were established for dispersing organic montmorillonite (OMMT) nanolayers into ethylene–propylene–diene rubber (EPDM) matrix in a HAAKE mixer. The experimental results of X-ray diffraction and transmission electron microscopy showed that the MMT modified with trimethyloctadecylamine or dimethylbenzyloctadecylamine existed in the form of an intercalated layer structure and the MMT modified with methlybis(2-hydroxyethyl)cocoalkylamine was fully exfoliated in the EPDM matrix. The expansion of the distance between the silicate layers firstly took place after the HAAKE mixing, then the silicate layers were exfoliated in the EPDM matrix after the EPDM/OMMT composite was cured. The EPDM/OMMT composites had good mechanical properties. The EPDM composite containing 15 phr OMMT which was modified with the alkylamine containing hydroxyl groups showed high tensile strength of 25 MPa. Dynamic mechanical analysis revealed that the glass transition temperature (Tg) of the composites was higher than that of gum EPDM vulcanizate. The OMMTs had delaying effects on the vulcanization reaction and decreased the crosslink density of the EPDM/OMMT composites.

In situ preparation of zinc salts of unsaturated carboxylic acids to reinforce NBR

Through the neutralization reaction of zinc oxide (ZnO) and methacrylic acid (MAA) or acrylic acid (AA), zinc methacrylate (ZMA) or zinc acrylate (ZA) was in situ prepared in nitrile rubber (NBR). The mechanical properties and crosslinking structure of the resulting peroxide-cured NBR vulcanizates were studied. The results showed that ZnO/MAA (AA) had a great reinforcing effect for NBR, and their amounts and ratio played important roles in influencing the mechanical properties. Such vulcanizate contains both covalent crosslinks and salt crosslinks, and the change in the tensile strength of the vulcanizate was related to the variation of the salt crosslink density.

A comparison between the SBR vulcanizates reinforced by magnesium methacrylate added directly or prepared in situ

The styrene–butadiene rubber (SBR) cured by dicumyl peroxide was reinforced by magnesium methacrylate [Mg(MAA)2], which was added into SBR directly or prepared in situ in SBR through the neutralization of magnesium oxide (MgO) and methacrylic acid (MAA). The experimental results show that the SBR vulcanizates reinforced by Mg(MAA)2 prepared in situ have better mechanical properties than those reinforced by Mg(MAA)2 added directly. The SBR vulcanizates with Mg(MAA)2 prepared in situ are semi-transparent, but those with Mg(MAA)2 added directly are opaque. The Fourier transform infrared analysis shows that the polymerization conversion of Mg(MAA)2 in the SBR vulcanizates with Mg(MAA)2 prepared in situ is much higher than that in the SBR vulcanizates with Mg(MAA)2 added directly. The scan probe microscopy photographs show that the particles in the SBR vulcanizates with Mg(MAA)2 prepared in situ are much finer and disperse more evenly than that in the SBR vulcanizates with Mg(MAA)2 added directly.

Effect of magnesium methacrylate on the mechanical properties of EVM vulcanizate

Abstract High performance ethylene-vinyl acetate copolymer (EVM) vulcanizate was obtained by directly blending EVM with magnesium methacrylate (MDMA) at a high level. The mechanical properties and crosslink density of the peroxide-cured EVM vulcanizates were investigated. Dynamic mechanical thermal analysis (DMTA) was used to study dynamic properties of EVM reinforced by MDMA. The results showed that the commercial MDMA can greatly improve the modulus at 100% and tensile strength of the EVM vulcanizates, while retaining their high elongation at break. DMTA results revealed that the glass transition temperature ( T g ) of the vulcanizate shifted to lower temperature with the increase of MDMA loading. Fourier transform infrared (FTIR) spectrum indicated that the double bonds in MDMA reacted after peroxide curing. Crosslink density analysis showed that EVM vulcanizate contained both ionic bonds and covalent bonds. Ionic crosslinks greatly increased with increasing amount of MDMA and dicumyl peroxide (DCP).

Dynamically vulcanized nitrile rubber/polyoxymethylene thermoplastic elastomers

A new compatibilized method was used to prepare thermoplastic elastomer (TPE) of nitrile rubber (NBR) and polypropylene (PP) with excellent mechanical properties by dynamic vulcanization. Glycidyl methacrylate (GMA) grafted PP/amino-compound was used as a compatibilizer. The effects of the curing systems, compatibilizer, PP type, and reprocessing on the mechanical properties of NBR/PP thermoplastic elastomers were investigated in detail. Experimental results showed that the addition of amino-compound in the compatibilzer can significantly increase the mechanical properties of the NBR/PP thermoplastic elastomer. Compared with other amino-compounds, diethylenetriamine (DETA) has the best effect. PP with higher molecular weight is more suitable for preparing NBR/PP thermoplastic elastomer with high tensile strength and high elongation at break.

Metallic methacrylate as a reactive filler to reinforce ethylene-propylene-diene rubber

The reinforcement of non-polar ethylene-propylene-diene rubber (EPDM) by the polar metal salts of methacrylic acid was achieved by directly mixing the salt into EPDM at a high level and curing with peroxide. Mechanical properties and crosslink density of the vulcanizates were investigated. Wide-angle X-ray diffraction (WAXD) and Fourier transform-infrared spectroscopy (FTIR) were employed to analyze the reactivity of zinc dimethacrylate (ZDMA) in EPDM compounds before and after vulcanization. It was observed that the commercial ZDMA or magnesium dimethacrylate (MDMA) can greatly improve the hardness and tensile strength of the EPDM vulcanizates, while retaining a high elongation at break. WAXD and FTIR revealed that ZDMA is a reactive filler in the EPDM matrix during peroxide curing. The crosslink density of the vulcanizates was determined by equilibrium swelling. Covalent crosslinks and ionic crosslinks were distinguished by an acidolysis treatment. Ionic crosslinks were greatly improved by increasing the amount of zinc dimethacrylate or dicumyl peroxide, and the relationship between mechanical properties and crosslink density indicates that the tensile strength of the vulcanizate was principally dependent on ionic crosslink density.

A Comparison between Cure Systems for EPDM/Montmorillonite Nanocomposites

Two kinds of ethylene-propylene-diene rubber (EPDM)/organic montmorillonite (OMMT) nanocomposites were prepared with two kinds of cure systems: sulfur and peroxide. The experimental results from X-ray diffraction and transmission electron miscroscopy showed that EPDM intercalated the MMT galleries and the MMT was exfoliated and dispersed uniformly in the EPDM composites cured with sulfur. But the MMT was stacked with several layers and existed in an intercalated structure in the EPDM composites cured with peroxide. The EPDM composites cured with sulfur were opaque and had better mechanical properties, while the EPDM composites cured with the peroxide were semi-transparent. Vulcametric curves showed that the MMT retarded the vulcanization reaction of the EPDM composites cured with the sulfur cure system, and furthermore, gave rise to a marked decrease in maximum torque, indicating a lower crosslink density. This was confirmed by swelling measurements. But the corresponding values of the composites cured with the peroxide cure system were virtually unchanged by addition of the OMMT.

Structure and properties of BR nanocomposites reinforced with organoclay

Butadiene rubber (BR)/organoclay nanocomposites were prepared by direct melt mixing of BR and clay modified with different primary and quaternary ammonium salts. BR/pristine clay composite and BR/organoclay nanocomposites were analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The vulcanization characteristics and the mechanical properties of the BR/pristine clay and BR/organoclay composites were investigated. The results showed that the interlayer distance of the organoclays was expanded, which indicated that intercalated BR/organoclay nanocomposites had been prepared. Organoclay effectively accelerated the vulcanization of BR, which was attributed to the intercalatant used to modify the clay. The tensile strength, elongation at break and tear strength of BR/organoclay nanocomposites are much higher than those of gum BR vulcanizate and BR/pristine clay composites. The organoclay modified with dimethyl dihydrogenated tallow ammonium chloride (DDAC) gave the best reinforcement effect in BR of all the organoclays.

Preparation and properties of semi-transparent EPDM/montmorillonite nanocomposites

Ethylene-propylene-diene rubber (EPDM)/organic montmorillonite (OMMT) nanocomposites were prepared through a melt-mixing process in an internal mixer. The nanoscale dispersion of OMMT in the EPDM matrix was verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM), relating to an exfoliated morphology. The effects of OMMT content on the mechanical properties, curing behaviour, optical properties and thermal properties of the EPDM/OMMT nanocomposites were studied. The experimental results showed that OMMT had good reinforcement on the EPDM vulcanizates. The tensile strength and tear stress of the EPDM/OMMT nanocomposites significantly increased with increasing OMMT content. When the OMMT content was 15 phr, the tensile strength and elongation at break reached 19.8 MPa and 540%, respectively. The EPDM/OMMT nanocomposite cured by 2,5-dimethyl-2, 5-bis (tert-butyl peroxy) hexane was semi-transparent and the OMMT content had little influence on the curing behaviour of the nanocomposites. The increases in the glass transition temperature and thermal decomposition temperature were observed in the nanocomposites and were supposed to be related with the nanoscale dispersion of the OMMT and the strong interaction between EPDM and OMMT. Moreover, the permeability of oxygen for the EPDM/OMMT nanocomposites was reduced remarkably.

Preparation and properties of a water-swelling rubber by in situ formed lithium acrylate in nitrile rubber

Lithium acrylate (LiAA) was in situ prepared in nitrile rubber (NBR) through neutralization of lithium hydroxide (LiOH) and acrylic acid (AA) during mixing. The NBR/LiAA compounds were vulcanized with dicumyl peroxide (DCP). The in situ preparation and polymerization of LiAA were characterized using Fourier transform infrared (FTIR) spectrometer. The micrographs of the compounds and vulcanizates were explored using a scanning electron microscope (SEM). The effects of DCP and LiAA contents on the water-swelling and mechanical properties of the vulcanizates were studied. The relationship between the LiOH/AA molar ratio and the properties of the vulcanizates was investigated. The results showed that the in situ formed LiAA could improve the mechanical properties and water–swelling properties of the NBR/LiAA vulcanizates. The vulcanizates properly compounded had high water-swelling ratio over 800% and tensile strength more than 12MPa. The differential scanning calorimetry (DSC) measurements indicated that the water absorbed in the vulcanizate existed in PLiAA and NBR networks in three different physical states, namely, free water, freezable bound water and non-freezable bound water.