Cross-linked Rubber Research Articles

Influence of network structure on the viscoelastic properties of dynamically vulcanized rubber/plastic blends: An alternative approach to understand the microstructure evolution

The formation of finely dispersed micron-sized cross-linked rubber agglomerates in the thermoplastic matrix during dynamic vulcanization is now a well accepted theory to explicate the final properties of thermoplastic vulcanizates (TPVs). Based on our previous results, we have investigated further in the present work on the most influential and essential parameters which controls the ultimate properties of the TPVs. Three TPVs based on poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymer (S-EB-S) and solution polymerized styrene butadiene rubber (S-SBR) have been prepared containing different proportions of rubber fraction. A semi-efficient (SEV) sulphur based curing system has been adopted to cross-link the rubber phase and advanced microscopic techniques viz. transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) have been used for the microstructure analysis. Thereafter, dynamic experiments have been performed to correlate the morphological observations with viscoelastic properties. The experimental results and the morphological images confirm that the network structure formation during dynamic vulcanization and its integrity is the most influential parameter to cause the utmost properties of the TPVs. The finely dispersed cross-linked rubber particles obtained during dynamic vulcanization are actually the disintegrated and agglomerated rubber nano-particles having average particle size between 80 and 85nm. It has also been confirmed that the integrated rubber network structure has an inverse relationship with the proportion of rubber fraction present in the TPVs. Mechanical properties, melt rheology and dynamic viscoelastic measurements also support the network structure disruption and disintegration observed in the morphological images and thus, nullifies the supremacy of dispersed phase morphology theory behind the superior properties obtained from the TPVs. This work elucidates the necessity and importance of integrated network structure formation over the morphology evolution during dynamic vulcanization and leads to a new avenue to understand morphology–mechanical–rheological–viscoelastic property correlation in TPVs.

Low-Power Upconversion in Poly(Mannitol-Sebacate) Networks with Tethered Diphenylanthracene and Palladium Porphyrin

Efforts to fabricate low-power upconverting solid-state systems have rapidly increased in the past decade because of their possible application in several fields such as bio-imaging, drug delivery, solar harvesting or displays. The synthesis of upconverting cross-linked polyester rubbers with covalently tethered chromophores is presented here. Cross-linked films were prepared by reacting a poly(mannitol-sebacate) pre-polymer with 9,10-bis(4-hydroxymethylphenyl) anthracene (DPA-(CH2OH)2) and palladium mesoporphyrin IX. These chromophores served as emitters and sensitizers, respectively, and through a cascade of photophysical events, resulted in an anti-Stokes shifted emission. Indeed, blue emission (~440 nm) of these solid materials was detected upon excitation at 543 nm with a green laser and the power dependence of integrated upconverted intensity versus excitation was examined. The new materials display upconversion at power densities as low as 32 mW/cm2, and do not display phase de-mixing, which has been identified as an obstacle in rubbery blends comprising untethered chromophores. ToC Low-power upconverting cross-linked polyester with tethered chromophores was synthesized by polycondensation of poly(mannitol-sebacate) pre-polymers with 9,10-bis(4-hydroxymethylphenyl) anthracene and palladium mesoporphyrin IX. Upconverted blue fluorescence (440 nm) of these solid materials is detected upon excitation at 543 nm with a green laser and the power dependence of integrated upconverted intensity versus excitation is examined in this study.

Stress relaxation, creep and set recovery of elastomers

The stress relaxation, creep and recovery behaviour of a cross-linked unfilled natural rubber has been investigated at moderate stresses in tension. The aim being to extend the idea, initially developed by Alan Gent in his seminal 1962 paper on the relaxation behaviour of rubber, in order to understand and examine the time dependent mechanisms that are present in elastomers under strain. A method based upon the Boltzmann superposition principle was used to compare the creep compliance with a measurement of its recovery after release from a range of constant loads held for different times. The creep behaviour was seen to exhibit the usual linear dependence on the logarithm of time. The recovery data was also seen to reduce onto a single recovery curve for any given applied tensile stress for a range of loading times using the Boltzmann superposition principle. The differences between the relative rates of the creep and the recovery behaviour can in part be attributed to the non-linearity in the stress–strain behaviour exhibited in tension of the elastomer.

The impact of strain-induced crystallization on strain during mechanical cycling of cross-linked natural rubber

The improvement of X-ray diffraction techniques since the last ten years allowed a renewal of the study of strain-induced crystallization in natural rubber. In particular real-time measurements are now commonplace. However, due to experimental difficulties, the exploitation of the X-ray data as far as the strain state of the remaining molten fraction is concerned has been left aside. Indeed the knowledge of the local extension of the molten chains is crucial for understanding the peculiar stress behavior observed during the crystallization process. This paper presents a systematic study of this parameter during mechanical cycling performed at various temperatures. It is shown that crystallization limits the amplitude of strain endured by the molten fraction during traction. This process of strain regulation may be one explanation for the protective effect of crystallization against tearing. A precise evaluation of the contribution of the molten fraction to the retraction force during mechanical cycling is made. The role of crystallites as nanofillers may be quantified this way.

Fabrication of conductive elastic nanocomposites via framing intact interconnected graphene networks

Electrically conductive elastic nanocomposites with well-organized graphene architectures offer significant improvement in various properties. However, achieving desirable graphene architectures in cross-linked rubber is challenging due to high viscosity and cross-linked nature of rubber matrices. Here, three dimensional (3D) interconnected graphene networks in natural rubber (NR) matrix are framed with self-assembly integrating latex compounding technology by employing electrostatic adsorption between poly(diallyldimethylammonium chloride) modified graphene (positively charged) and NR latex particles (negatively charged) as the driving force. The 3D graphene structure endows the resulted nanocomposites with excellent electrical conductivity of 7.31 S/m with a graphene content of 4.16 vol.%, extremely low percolation threshold of 0.21 vol.% and also analogous reinforcement in mechanical properties. The developed strategy will provide a practical approach for developing elastic nanocomposites with multi-functional properties.

Peroxide vulcanization of natural rubber. Part I: effect of temperature and peroxide concentration

Abstract Four different peroxides as curing agents were used to prepare vulcanizates based on natural rubber (NR). The effects of temperature and peroxide concentration on the vulcanization characteristics of rubber compounds, cross-link density (ν) and physical-mechanical properties of equivalent vulcanizates were investigated. The results revealed that the vulcanization temperature and also the relative amount of peroxide decomposition products are of significant importance in the properties of vulcanizates. Lower vulcanization temperature and lower concentration of peroxides were found to be better factors, showing a proper balance between the degree of cross-linking of the rubber and degradation of the macromolecular chains by side reactions in relation to the crystallization of NR, which imparts vulcanizates based on NR outstanding properties.

Mechanistic aspects of silane coupling agents with different functionalities on reinforcement of silica‐filled natural rubber compounds

Silane coupling agents containing different specific functionalities are studied to gain understanding of their roles in silica‐filled natural rubber (NR) compounds. Five different silane coupling agents, that is bis‐(triethoxysilylpropyl) tetrasulfide (TESPT), bis‐(triethoxysilylpropyl) disulfide (TESPD), octyltriethoxysilane, vinyltrimethoxysilane, and bis‐(trimethyl‐silylmethyl) tetrasulfide (TMSMT), are comparatively investigated, by taking the most commonly used TESPT as a reference. The results reveal that alkoxy‐based silanes can effectively reduce the filler–filler interaction and lower compound viscosity owing to the effect of silane‐to‐silica hydrophobation which contributes to better compatibility between silica and NR. The alkoxy‐silanes with a sulfur moiety, that is TESPT and TESPD, show more pronounced improvement in overall properties as a result of filler–rubber interactions. The use of TMSMT which has no alkoxy groups but contains only a sulfur moiety elucidates that there are three reaction mechanisms involved in systems with sulfur‐alkoxy‐based silane. These are as follows: (1) the silane‐to‐silica or silanization/hydrophobation reaction; (2) the silane‐to‐rubber or coupling reaction; and (3) rubber–rubber crosslinking originating from active sulfur released by the polysulfide‐based silane TESPT. These simultaneous reactions are temperature dependent, and show an optimum level at a dump temperature of approximately 140–150°C, as depicted by filler–filler and filler–rubber interactions, as well as mechanical properties of such compounds. POLYM. ENG. SCI., 55:836–842, 2015. © 2014 Society of Plastics Engineers

Dependence of Adhesion Properties of Cross-linked Epoxidized Natural Rubber (ENR 25)-Based Pressure-Sensitive Adhesives on Benzoyl Peroxide Loading in the Presence of Gum Rosin and Petroresin Tackifiers

The effect of benzoyl peroxide loading on the adhesion properties of cross-linked epoxidized natural rubber (ENR 25)-based adhesives was studied using gum rosin and petroresin as tackifiers. Toluene and polyethylene terephthalate (PET) were used as solvent and coating substrate, respectively. The adhesion properties were determined by a Lloyd adhesion tester operating at 30 cm min−1. Results indicate that the loop tack and peel strength of gum rosin and petroresin pass through a maximum value at 2 parts per hundred parts of rubber (phr) and 3 phr benzoyl peroxide concentration, respectively, an observation which is attributed to the optimum cross-linking of ENR 25 where optimum, cohesive and adhesive strength is obtained. The shear strength, however, increases steadily with increasing benzoyl peroxide loading due to the steady increase in the cohesive strength. At the optimum benzoyl peroxide concentration, the petroresin-based adhesive consistently exhibits higher adhesion properties compared to that of gum rosin-based adhesives. The adhesion properties of both adhesive systems increase with increasing coating thickness.

Phase morphologies of vulcanized chlorobutyl rubber/polyamide 12 blends: The breakup of pre‐crosslinked CIIR phase

ABSTRACTDynamic vulcanization to prepare blended thermoplastic vulcanizates (TPV) is a kind of complicated blending technology, where the breakup of the rubber phase happens accompanying with the crosslinking of rubber. In this study, we aim to investigate the effect of crosslinking on the breakup of chlorobutyl rubber (CIIR) phase in thermoplastic polyamide 12 (PA 12) matrix by purposely using pre‐crosslinked CIIR with different crosslink degrees and plasticizer contents. Besides, the effect of blending conditions on the breakup of crosslinked CIIR phase was studied. The results show that a low crosslink degree, a high content of plasticizer, a low blending temperature and a morderate rotor speed of 70 rpm facilitate the breakup of pre‐crosslinked CIIR in PA 12 matrix. This is ascribed to the decrease in the modulus of pre‐crosslinked CIIR phase because of either a low crosslink degree or a high content of plasticizer, the increase in the molten viscosity of thermoplastic matrix because of a low blending temperature and a moderate rotor speed. It is indicated that the breakup of pre‐crosslinked rubber is mainly dominated by the modulus of crosslinked rubber phase as well as the molten viscosity of thermoplastic matrix and shear stress. This study will provide guidance for the preparation of CIIR/PA TPV. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40765.

Facile Fabrication of a Shape Memory Polymer by Swelling Cross-Linked Natural Rubber with Stearic Acid.

A facile method was developed for fabrication of a robust shape memory polymer by swelling cross-linked natural rubber with stearic acid. Commercial rubber bands were swollen in molten stearic acid at 75 °C (35 wt % stearic acid loading). When cooled the crystallization of the stearic acid formed a percolated network of crystalline platelets. The microscopic crystals and the cross-linked rubber produce a temporary network and a permanent network, respectively. These two networks allow thermal shape memory cycling with deformation and recovery above the melting point of stearic acid and fixation below that point. Under manual, strain-controlled, tensile deformation the shape memory rubber bands exhibited fixity and recovery of 100% ± 10%.

Dynamically Vulcanized Biobased Polylactide/Natural Rubber Blend Material with Continuous Cross-Linked Rubber Phase

We prepared a biobased material, dynamically vulcanized polylactide (PLA)/natural rubber (NR) blend in which the cross-linked NR phase owned a continuous network-like dispersion. This finding breaks the traditional concept of a sea-island morphology formed after dynamic vulcanization of the blends. The scan electron microscopy and dissolution/swell experiments provided the direct proof of the continuous cross-linked NR phase. This new biobased PLA/NR blend material with the novel structure is reported for the first time in the field of dynamic vulcanization and shows promise for development for various functional applications.

Acrylonitrile–butadiene rubber functionalization for the toughening modification of recycled poly(ethylene terephthalate)

ABSTRACTThe incorporation of functionalized acrylonitrile–butadiene rubber (NBR) into recycled poly(ethylene terephthalate) (PET) was introduced as an effective route for modifying the properties of PET and as a new method for PET recycling as well. To achieve modified NBR, glycidyl methacrylate (GMA) was grafted onto NBR with optimized reactive mixing, in which the highest grafting degree and lowest gel content were generated. PET/NBR blends with and without GMA functionalization were produced by melt mixing, and the mechanical properties, dynamic mechanical thermal properties, and phase morphologies of the systems were determined and compared. We found that low amounts of peroxide initiator (dicumyl peroxide) and high levels of the GMA monomer in the presence of the styrene comonomer led to the maximum grafting degree and suppressed the competing rubber crosslinking and GMA homopolymerization reactions. The blend compatibility with PET determined from dynamic mechanical thermal analysis spectra and scanning electron microscopy images was greatly improved when the NBR‐grafted GMA was used instead of the neat NBR in the blend recipes. As a result, the rubber phase dispersed in the PET matrix more finely, and the impact strength of the blend advanced very significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40483.

Novel thermoplastic vulcanizates (TPVs) based on silicone rubber and polyamide exploring peroxide cross-linking

Novel thermoplastic vulcanizates (TPVs) based on silicone rubber (PDMS) and polyamide (PA12) have been prepared by dynamic vulcanization process. The effect of dynamic vulcanization and influence of various types of perox- ides as cross-linking agents were studied in detail. All the TPVs were prepared at a ratio of 50/50 wt% of silicone rubber and polyamide. Three structurally different peroxides, namely dicumyl peroxide (DCP), 3,3,5,7,7-pentamethyl 1,2,4-triox- epane (PMTO) and cumyl hydroperoxide (CHP) were taken for investigation. Though DCP was the best option for curing the silicone rubber, at high temperature it suffers from scorch safety. An inhibitor 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) was added with DCP to stabilize the radicals in order to increase the scorch time. Though CHP (hydroperoxide) had higher half life time than DCP at higher temperature, it has no significant effect on cross-linking of silicone rubber. PMTO showed prolonged scorch safety and better cross-linking efficiency rather than the other two. TPVs of DCP and PMTO were made up to 11 minutes of mixing. Increased values of tensile strength and elongation at break of PMTO cross-linked TPV indi- cate the superiority of PMTO. Scanning electron micrographs correlate with mechanical properties of the TPVs. High stor- age modulus (E!) and lower loss tangent value of the PMTO cross-linked TPV indicate the higher degree of cross-linking which is also well supported by the overall cross-link density value. Thus PMTO was found to be the superior peroxide for cross-linking of silicone rubber at high temperature.

Crosslinking of Rubbers

Crosslinking of Rubbers

オゾン水処理による架橋シリコーンゴムの劣化における化学的変化

オゾン水処理による架橋シリコーンゴムの劣化における化学的変化

中性子散乱法を用いた加硫ゴムの架橋構造解析

中性子散乱法を用いた加硫ゴムの架橋構造解析

ナノフィラー充塡架橋ゴムにおけるナノフィラーの構造と物性

ナノフィラー充塡架橋ゴムにおけるナノフィラーの構造と物性

Properties of Vulcanized Polyisoprene Rubber Composites Filled with Opalized White Tuff and Precipitated Silica

Opalized white tuff (OWT) with 40 μm average particle size and 39.3 m2/g specific surface area has been introduced into polyisoprene rubber (NR). Their reinforcing effects were evaluated by comparisons with those from precipitated silica (PSi). The cure characteristic, apparent activation energy of cross-link (E ac) and reversion (E ar), and mechanical properties of a variety of composites based on these rubbers were studied. This was done using vulcanization techniques, mechanical testing, and scanning electron microscopy (SEM). The results showed that OWT can greatly improve the vulcanizing process by shortening the time of optimum cure (t c90) and the scorch time (t s2) of cross-linked rubber composites, which improves production efficiency and operational security. The rubber composites filled with 50 phr of OWT were found to have good mechanical and elastomeric properties. The tensile strengths of the NR/OWT composites are close to those of NR/PSi composites, but the tear strength and modulus are not as good as the corresponding properties of those containing precipitated silica. Morphology results revealed that the OWT is poorly dispersed in the rubber matrix. According to that, the lower interactions between OWT and polyisoprene rubber macromolecules are obtained, but similar mechanical properties of NR/OWT (100/50) rubber composites compared with NR/PSi (100/50) rubber composites are resulted.

架橋ゴムの伸長結晶化

架橋ゴムの伸長結晶化

ナノフィラー充塡架橋ゴムにおけるナノフィラーの構造と物性

ナノフィラー充塡架橋ゴムにおけるナノフィラーの構造と物性