Cross-linked Sodium Polyacrylate Research Articles

(Invited) SiO and LiNi0.5Mn1.5O4 Composite Electrodes with Functional Polymer Binders

This study focuses on the optimization of polymer binders in lithium-ion batteries (LIBs) to facilitate the development of high-energy-density storage devices. Despite 30 years of commercialization, the demand for high energy density storage devices has continued to increase, making LIBs a topic of significant research interest. One major avenue of research has focused on high-voltage positive electrode materials such as LiNi0.5Mn1.5O4 (LNMO) and high-capacity negative electrode materials like SiO. However, the practical use of these materials is hindered by issues associated with electrolyte decomposition and large volume changes during the charge-discharge process.To address these challenges, we explored the chemistry of polymer binders blended in composite electrodes to maintain the structure of the electrode and form a passivation/protective layer on the active material surface to suppress side reactions.(1, 2) In particular, we investigated the use of "functional binders" to improve the performance of high-voltage LNMO composite electrodes. We synthesized sulfated alginate binders, which are significantly cheaper and stiffer than commonly used poly(vinylidene fluoride) (PVdF) and uniformly cover the surface of LNMO.(3)The high polarity of the sulfate group also increased the binder's affinity for the electrolyte. During the initial charge-discharge cycle, the electrolyte decomposition products generated on the alginate-covered active materials participated in the formation of a protective passivation layer that suppressed further decomposition during subsequent cycles, resulting in enhanced cycling and rate performances.We also explored the use of partially-neutralized crosslinked sodium polyacrylate (CLPA) binders with flexible monomers to mitigate the effects of volume changes in SiO electrodes.(4)Additionally, we investigated the “maturation” effects on battery performances by storing the composite electrodes with CLPA-based binders in a humid atmosphere for a few days before drying. Our results show that the binder with 20% flexible monomer (CLPA-20) exhibited the highest peel strength and long-term cyclability, and the maturation treatment further improved these properties. Cross-sectional SEM images revealed that the binder and conductive carbon were uniformly dispersed in the composite layer in the matured electrodes, indicating the migration of active materials and binders during the maturation process. Furthermore, surface analysis of the cycled electrode showed that the superior mechanical properties of the electrode endowed by the maturation treatment helped in maintaining the passivation layer on the active material surface, resulting in improved cycling performance.Overall, our findings suggest that optimizing polymer binders can enhance the performance of LIBs by controlling the electrode reaction via binder chemistry. The strategies developed in this study could facilitate the future development of high-energy-density LIBs, making them more accessible and commercially viable for various applications.References (1) R. Tatara, S. Komaba et al., ChemElectroChem, 8, 4345 (2021).(2) H. Isozumi, R. Tatara, S. Komaba et al., ACS Appl. Energy Mater., 3, 7978 (2020).(3) A. Oishi, R. Tatara, S. Komaba et al., ACS Appl. Mater. Interfaces, 14, 51808 (2022).(4) S. Yamazaki, R. Tatara, S. Komaba et al., Mater. Adv., 4, 1637 (2023).

Diapers to Thickeners and Pressure-Sensitive Adhesives: Recycling of Superabsorbers via UV Degradation.

Superabsorbers based on crosslinked sodium polyacrylate polymers cannot be easily recycled, resulting in 2 million tons of superabsorbers being landfilled or burned every year. A fast and efficient strategy to recycle superabsorbers would significantly alleviate environmental pollution and promote a sustainable use of these polymers. Herein, the rapid recycling of crosslinked sodium polyacrylate hydrogels based on their inherent UV degradation is demonstrated without the need for chemicals besides water. A quantitative conversion of crosslinked sodium polyacrylate into soluble sodium polyacrylate is achieved in minutes, almost 200 times faster than a previous approach based on de-esterification. The obtained soluble sodium polyacrylate can be used, for example, as a thickener for aqueous dyes or can be esterified with n-butanol or 2-ethylhexanol to serve as a pressure-sensitive adhesive. The UV photodegradation and esterification of superabsorbers is fast, scalable, safe, and economical and yields polymers with controllable molecular weight in the range of 100-400 kg/mol. It thus offers distinct advantages over the chemical de-crosslinking strategies presented previously.

Er:YAG Laser Physical Etching and Ultra-High-Molecular-Weight Cross-Linked Sodium Polyacrylate Chemical Etching for a Reliable Dentin Dry Bonding.

Dentin bond interface stability is the key issue of dental adhesion in present clinical dentistry. The concept of selective extrafibrillar demineralization has opened a new way to maintain intrafibrillar minerals to prevent interface degradation. Here, using ultra-high-molecular-weight sodium polyacrylate [Carbopol (Carbo) > 40 kDa] as a calcium chelator, we challenge this concept and propose a protocol for reliable dentin dry bonding. The results of high-resolution transmission electron microscopy revealed periodic bands of 67 nm dentin collagen fibrils after Carbo etching, and the hydroxyproline concentration increasing with prolonged chelating time denied the concept of extrafibrillar demineralization. The results that wet and dry bonding with Carbo-based demineralization produced a weaker bond strength than the traditional phosphoric acid wet adhesion suggested that the Carbo-based demineralization is an unreliable adhesion strategy. A novel protocol of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion revealed that a micro-/nano-level rough, rigid, and non-collagen exposed dentin surface was produced, the micro-tensile bond strength was maintained after aging under dry and wet bonding modes, and in situ zymography and nanoleakage within the hybrid layers presented lower signals after aging. Cell culture in vitro and a rabbit deep dentin adhesion model in vivo proved that this protocol is safe and biocompatible. Taken together, the concept of extrafibrillar demineralization is limited and insufficient to use in the clinic. The strategy of Er:YAG laser physical etching followed by Carbo chemical etching for dentin adhesion produces a bonding effect with reliability, durability, and safety.

Understanding the shrinkage behaviour of alkali-activated slag binders modified by the superabsorbent polymer

Superabsorbent polymers (SAPs) have gained attention as internal curing agents in alkali-activated slags (AAS). The absorption–desorption kinetics of SAPs in AAS pastes were monitored using X-ray computed tomography. This study examines the influence of Angular covalently crosslinked sodium polyacrylate SAPs on AAS's reaction kinetics, pore structure, and microstructure f AAS. Meanwhile, autogenous, total drying shrinkage and continuous monitoring of internal relative humidity changes were performed. The results showed that the SAPs’ desorption kinetics is crucial in influencing the efficiency to counteract the shrinkage. SAPs significantly mitigated the autogenous and total drying shrinkage up to 90% and 30%, respectively.The incorporation of the ideal content of SAPs significantly compensated for the impact of the w/b ratio AAS properties. The optimum SAPs dosage was found to be 0.6 %, which enhanced the ability to control IC water, yielding better performance in terms of shrinkage, assisting the hydration degree, and enhancing the surface quality and anti-permeability. No reaction products were detected inside the voids of SAP, and the agglomeration of SAP was observed. However, care should be taken when incorporating a high content of SAP (i.e. > 0.6 %), which can adversely affect the properties of AAS. This work confirms that IC of AAS using SAPs is a powerful mitigating strategy, particularly when traditional curing is insufficient.

Multi-scale structure of in-situ polymerized cementitious composites with improved flowability, strength, deformability and anti-permeability

In-situ polymerization of polymers with cement can greatly improve the engineering performances of cementitious composites, the structural mechanisms, however, remain still not fully established. Herein in-situ polymerization modified cementitious composites (iPMCC) with sodium acrylate (SA) in different dosages (0%, 4% and 8%) were fabricated. Flowability, strength, deformability, and water sorptivity of the iPMCCs were tested, and the multi-scale structures in terms of pore size distribution, microscopic morphology, chemical characteristics, and solid structure of calcium-silicate (-aluminate)-hydrates were characterized. Results demonstrate that, compared with neat cement paste, the iPMCC with 4% SA showed the improvement of flowability by 35.1%, the increases of flexural and compressive strength by 109.0% and 11.8%, the rises of flexural and compressive deformation energy by 458.8% and 161.0%, and the decrease of water sorptivity by 19.1%. The in-situ SA polymerizations lead to substantial pore refinement, but macro defects in the iPMCC with 8% SA. Cross-linked sodium polyacrylate networks formed in the cement matrix and interacted with the cement hydrates, accounting for the improved strength, deformability, and water resistance. Cement hydration depression by polymers was evidently supported by the NMR data. The findings would deepen the understandings of multi-scale structure of cementitious composites with polymers, enabling development of highly ductile and durable construction materials.

Hydraulic Performance of Geosynthetic Clay Liners Comprising Anionic Polymer–Enhanced Bentonites

The hydraulic performance of geosynthetic clay liners (GCLs) comprising anionic polymer–enhanced bentonites (EBs), or EB-GCLs, based on permeation with 500 mM NaCl and 167 mM CaCl2 at an average effective stress of 27 kPa and hydraulic gradients of ∼300 was evaluated. The EBs included powdered sodium bentonite (NaB) enhanced with one of seven anionic polymers, including linear, noncrosslinked poly(acrylic acid) (PA) with low, medium, and high molecular weights, sodium carboxymethylcellulose (CMC) with either low viscosity or high viscosity, a covalently crosslinked sodium polyacrylate, and an in situ polymerized bentonite polymer composite. The NaB was enhanced with polymer at mass loadings of 5%, 8%, or 10% using dry-sprinkling, dry-mixing, and/or wet-mixing methods. Hydraulic conductivity tests at a low hydraulic gradient (∼35) also were conducted to determine the effect of seepage forces. Overall, the hydraulic performance of the EB-GCLs to the NaCl solution was better than that to the CaCl2 solution. Dry sprinkling (DS) with PA generally provided the best hydraulic performance, with hydraulic conductivity values based on permeation with 500 mM NaCl and 167 mM CaCl2 of 1.3×10−11 and 4.0×10−11 m/s, respectively, for the high-molecular-weight PA added at 5% via DS and 2.9×10−11 and 4.7×10−11 m/s, respectively, for the medium-molecular-weight PA added at 8% via DS. The CMC viscosity grade did not affect the hydraulic conductivity of the EB-GCLs. All EB-GCLs eluted polymer during permeation, regardless of mixing method or polymer type. Polymer elution was correlated with preferential interaggregate flow paths in multiple EB-GCL specimens, indicating the importance of polymer retention in maintaining low hydraulic conductivity of EB-GCLs. Because standard termination criteria for the measurement of the hydraulic conductivity of conventional unenhanced GCLs (e.g., as per current ASTM standards) do not address the potential impact of polymer elution from EB-GCLs, caution should be exercised when adapting these criteria to measure the hydraulic conductivity of EB-GCLs such as those evaluated in this study.

A Flexible Asymmetric NaFePO4/Carbon Cloth Supercapacitor Using Crosslinked Polyacrylate Gel as Electrolyte

AbstractWith the development of light‐weight and bendable electric devices, nowdays, solid‐state supercapacitive devices have attracted great attention, in which the classic polymeric electrolytes such as polyvinyl alcohol and polyethylene oxide copolymers are generally used. However, the microphase separation in these polymers and low conductivity affect the ions transfer and the energy‐storage performance. In this work, a crosslinked sodium polyacrylate gel (NaPA) is synthesized to replace conventional polymeric electrolyte. Because NaPA is a kind of polymeric salt which has high native degree of ionization in water, the NaPA gel shows low resistance to ion transportation. By using NaPA gel as the electrolyte and carbon cloth as current collector, a flexible solid asymmetric supercapacitor assembled by positive NaFePO4/carbon cloth and negative activated carbon/carbon cloth electrode shows the maximum capacitance of 46.33 mF cm−2 at 1 mA cm−2, with a high stability of 87.33 % retention during 5000 charge and discharge cycles. Moreover, this flexible asymmetric supercapacitors showed nearly unchanged capacitance under different bending angles. It is found that the Na+ diffusion coefficient in NaFePO4/CC//NaPA supercapacitor is 8.05×10−14 cm2 ⋅ s, remarkable higher than CC//NaPA and NaFePO4/CC//PVA. The high diffusion coefficient and low resistance of NaPA lead to excellent capacitave performance of NaFePO4/CC//NaPA, delivering a good application prospect.

Transforming superabsorbant polymers to super sticky notes

Upcycling plastics enables the design of value-added materials, a distinct alternative to landfilling. A recently published article in <i>Nature Communications</i> (McNeil et al.) reports a sustainable metamorphosis of crosslinked sodium polyacrylate, the superabsorbent material in diapers, into adhesives. Life cycle analyses of the several operationally simple transformations emphasize environmental consciousness.

Exceptional cold-crystallization kinetics of erythritol-polyelectrolyte enables long-term thermal energy storage

Long-term thermal energy storage balances the seasonal variations in renewable energy supply and demand, but applied storage concepts require improved performance in efficiency, reliability and capacity. In principle, supercooling and cold-crystallization offer a way to store heat for an extensive amount of time. In this approach, crystallization behaviour of the material governs the storage performance, as it directly relates to optimal efficiency, length of the storage period and heat release properties. This work explains the unique cold-crystallization behaviour of erythritol in cross-linked sodium polyacrylate. To this end, isothermal cold-crystallization was measured experimentally and analysed with the Avrami equation. Although the cold-crystallization rate constant follows the Arrhenius equation, it drastically decreases near the glass transition region and diverges from the equation. Thermal history also influences the cold-crystallization behaviour. Increases in cooling end-temperature reduce the subsequent crystallization time and promote metastable polymorph formation. These findings stem from the peculiar energy landscape of erythritol in cross-linked sodium polyacrylate. The landscape is classified as kinetically strong and thermodynamically fragile, which facilitates long-term thermal energy storage. Consistent supercooling and cold-crystallization behaviour of the material enables predicting the time-dependent crystallization rate at different temperatures. This confirms applicability of the two-stage Arrhenius-VFT model for temperature dependence and supports storage design in real-life applications. • Cold-crystallizing PCM for long-term TES with 230–350 MJ/m 3 storage capacity. • Spherical cold-crystallization enables modelling and predicting the kinetics. • Cold-crystallization follows Avrami equation and combined Arrhenius-VFT dependency. • Crystallization rate decreases drastically when approaching glass transition region. • Reducing cooling temperature increases following isothermal crystallization rate.

Tri‐Layer Laminated Fabric‐Induced Sweating Surfaces for Passive Cooling

AbstractFabrics which can keep people cool in a hot climate have attracted considerable attention in recent years. Among various cooling strategies, fabric cooling by water evaporation is proved to be very safe, simple and sustainable. Here, a tri‐layer laminated fabric (TLF) inspired by perspiration is designed to realize passive cooling of human body. An interlayer fabric which is coated with crosslinked sodium polyacrylate can absorb and store a large amount of water. A moisture‐absorbing and quick‐drying fabric is used as the outer layer while a waterproof breathable fabric is used on the inside of the laminate in contact with skin. The prepared TLF shows decent evaporative cooling performance under dry heat conditions. The water absorbency of TLF is about 400% higher than that of pristine cotton after 1 h soaking in water. Under a 1 sun irradiation (1000 W m−2), the indoor temperature of a simulated room can be reduced by ≈5–7 °C compared with the other without a cooling system. Meanwhile, the evaporative cooling effect can be maintained up to 5 h. This cooling fabric shows broad application prospects in the fields of thermal cooling to human and buildings.

A versatile cell-friendly approach to produce PLA-based 3D micro-macro-porous blends for tissue engineering scaffolds

In this study we instituted an innovative, cost-effective, green and versatile methodology to produce a series of PLA-based open-pore porous blends with high porosity and interconnectivity as well physico-mechanical properties suitable for tissue engineering application. Parent poly-l-lactic acid (PLA) blend was prepared by melt-blending using crosslinked sodium polyacrylate particles as a porogen, commonly used as superabsorbent polymer (SAP). The obtained biphasic systems showed a regular distribution of SAP particles with diameters up to about 50 µm and, most importantly, retained their superabsorbent ability within the thermoplastic PLA based matrices that facilitated swelling followed by leaching out from PLA based matrices in aqueous environment generating very high porosity. Very importantly, versatility of this developed methodology was judged by accommodating different polymers, such as, poly (3-hydroxybutyrate) (PHB) poly (ɛ-caprolactone) (PCL) or poly (ethylene glycol) (PEG) or wood-cellulose microfiber (SP) to generate monophasic, biphasic, plasticized or reinforced blends, respectively, under identical benign condition. These blends were analyzed morphologically, thermally and mechanically to evaluate the degree of miscibility, thermal stability and mechanical property to apply as scaffolds in tissue engineering. Finally, all these scaffolds allowed good cell adhesion and proliferation during culture of mouse embryo fibroblasts cell line. Hence, this methodology of producing PLA-based polymeric system stunned with processability to accommodate other biocompatible polymers allows selectively modifying biomaterial properties for target application and appears very promising platform for several applications, particularly for scaffold production in tissue engineering.

A Versatile Cell-Friendly Approach to Produce PLA-Based 3D Micro-Macro-Porous Blends for Tissue Engineering Scaffolds

In this study we instituted an innovative, cost-effective, green and versatile methodology to produce a series of PLA-based open-pore porous blends with high porosity and interconnectivity as well physico-mechanical properties suitable for tissue engineering application. Parent poly-L-lactic acid (PLA) blend was prepared by melt-blending using crosslinked sodium polyacrylate particles as a porogen, commonly used as superabsorbent polymer (SAP). The obtained biphasic systems showed a regular distribution of SAP particles with diameters up to about 50 μm and, most importantly, retained their superabsorbent ability within the thermoplastic PLA based matrices that facilitated swelling followed by leaching out from PLA based matrices in aqueous environment generating very high porosity. Very importantly, versatility of this developed methodology was judged by accommodating different polymers, such as, poly (3-hydroxybutyrate) (PHB) poly (ɛ-caprolactone) (PCL) or poly (ethylene glycol) (PEG) or wood-cellulose microfiber (SP) to generate monophasic, biphasic, plasticized or reinforced blends, respectively, under identical benign condition. These blends were analyzed morphologically, thermally and mechanically to evaluate the degree of miscibility, thermal stability and mechanical property to apply as scaffolds in tissue engineering. Finally, all these scaffolds allowed good cell adhesion and proliferation during culture of mouse embryo fibroblasts cell line. Hence, this methodology of producing PLA-based polymeric system stunned with processability to accommodate other biocompatible polymers allows selectively modifying biomaterial properties for target application and appears very promising platform for several applications, particularly for scaffold production in tissue engineering.

Influence of Effective Water-to-Cement Ratios on Internal Damage and Salt Scaling of Concrete with Superabsorbent Polymer.

Superabsorbent polymer (SAP) is attracting attention as a water-entraining admixture that reduces shrinkage or heals cracks in concrete. Cross-linked sodium polyacrylate SAPs, which are the most widely produced SAPs in the global market, are applicable as concrete admixtures. However, there have been contradictory results on the freeze–thaw resistance of concrete with SAPs. This study aims to clarify these results considering the water absorption behavior of SAPs in hardened concrete when effective water-to-cement ratios are different. Firstly, the absorbencies of one kind of cross-linked sodium polyacrylate SAP (SAP_SP) in pore solution and fresh mortar were measured by a tea bag test and flow test, respectively. Pore size distribution, capillary water absorption, and deformation during freeze–thaw cycles were analyzed for mortar samples with varying SAP_SP dosages. In the main tests, concrete samples with three different SAP_SPs/cement ratios (0.1%, 0.2%, and 0.3%) and a reference sample were prepared, and internal damage and salt scaling were measured under freeze–thaw cycles. Because SAP_SP absorbs water in fresh mixtures, additional water was added to the mixture considering the water absorbency of the SAP_SP. It was found that the used SAP_SPs prematurely release their stored water so the effective water-to-cement ratio was increased when a larger amount of SAP_SP was used. The higher effective water-to-cement ratio caused more internal damage and salt scaling due to the weaker cementitious matrix. In addition, mortar samples with a high SAP_SP content show a larger absorption of capillary water than the reference sample. The result can be interpreted by an observation that SAP_SP in air voids absorbs water and expands to relatively large capillary pores or neighbor air voids during the capillary water absorption process.

Features of aqueous polymer-stabilized foams particularly containing bentonite particles

Using self-foaming dispenser, wet aqueous foams were prepared from isoviscous solutions of sodium lauryl sulfate (SLS) with chemically distinct polymer stabilizers. Contribution of coalescence and Ostwald ripening to the foam decay was examined from photos and video data. The bubble coarsening was estimated by dispersion analysis using the Lifshitz–Slezov–Wagner equation. Water-soluble polymers were selected from typical thickeners and suspending agents. Xanthan gum, hydroxyethyl cellulose, polyacrylamide, cross-linked sodium polyacrylate, cross-linked and hydrophobically modified (meth)acrylate copolymers were tried as foam stabilizers. By the same way, xanthan gum and submicron bentonite particles were used as foam stabilizers. Stability of the foams containing mentioned polymers as well as xanthan plus bentonite studied by the photographs and dispersion analysis. The polymers characterize by their efficacy to stabilize the wet foam. Possible reasons for poor stabilization of the foam containing cross-linked polyacrylates, both hydrophilic and hydrophobically modified, are given. The behavior of polymer-containing foams and joint stabilizing action of xanthan and bentonite are explained by variations in the structure of foam films.

Cold-crystallization of polyelectrolyte absorbed polyol for long-term thermal energy storage

A lack of efficient crystallization methods and the metastability of supercooled liquids have limited the use of supercooling phase change materials (PCMs) in long-term thermal energy storage (LTES). Here, we propose a new supercooling PCM-polymer mixture that is not prone to spontaneous crystallization during the storage period. The material releases the stored thermal energy by cold-crystallization on re-heating. The PCM-polymer mixture is composed of supercooling polyol (erythritol or D-mannitol) dispersed in a cross-linked sodium polyacrylate (PAANa) matrix. PAANa efficiently prevents the conventional cooling crystallization of the PCM. Instead of crystallization, the melt polyol supercools and eventually vitrifies as an amorphous solid. Deeply supercooled or vitrified polyol is stable against crystallization below its cold-crystallization temperature. The heat charged and discharged remained similar in 100 repeated melting-crystallization cycles. Its good long-term performance and the stability of the supercooled polyol-PAANa against crystallization at low temperatures make the new material extremely promising for LTES.

Shrinkage and swelling behavior of archaeological waterlogged wood preserved with slightly crosslinked sodium polyacrylate

In this article, the conservation of archaeological waterlogged wood (WW) of Afzelia sp. (medium degraded: Umax = 385%) was impregnated in vacuum with an aqueous solution of acrylic acid (AA), sodium acrylate monomer (AANa), crosslinking agent (MBA) and catalyst (V-501). The simultaneous in situ polymerization and crosslinking resulted in slightly crosslinked sodium polyacrylate (PAANa) in the wood structure. The results showed that untreated WW had only a very limited ability to re-swell to recover its original dimensions from a collapsed condition, while WW protected by crosslinked PAANa could almost fully recover its original shape and size even after several drying–rewetting cycles. From microscopic observations, treated wood was found to maintain its original cell structure, form and shape even after repeated drying–rewetting cycles. PAANa was observed to be densely localized near the middle lamella, the cell corners, and the cell lumina by transmission electron microscopy observation. These observations suggest that our PAANa treatment provides reasonable strength as well as favorable hydrophilicity to avoid hornification of the cell wall upon drying, thus providing unique shape recovery properties.

Preparation and Characterization of Biodegradable Hydrogels Based on Ulvan, a Polysaccharide from Green Seaweeds

Preparation of superabsorbent hydrogels based on ulvan, a polysaccharide extracted from green seaweed Ulva, was investigated by crosslinking ulvan with divinylsulfone (DVS) under alkaline aqueous condition. Extraction of ulvan from Ulva was performed at room temperature or at 80°C. Gelation was observed constantly when ulvan obtained at 80°C was crosslinked with DVS, but not always when that obtained at room temperature was used. The optimal preparation condition of hydrogels was investigated by changing the feed amount of DVS. Among those examined, the highest water absorbency was obtained with the sample for DVS feed ratio of 20 wt%. Maximum absorbency in pure water was 80 g/g, which was considerably lower than that of crosslinked sodium polyacrylate, commercially available (300 g/g). Biodegradation speed of the hydrogels in the present study depended on the feed amount of DVS.

Development of solid super desiccants based on a polymeric superabsorbent hydrogel composite

The innovative design of cross-linked sodium polyacrylate based solid super-desiccant is demonstrating 276 ± 20% 24 h vapor absorption capacity at 99% RH.

Study on preparation and properties of water swellable rubber modified by interpenetrating polymer networks

A novel water swellable rubber (WSR) has been prepared by blending nitrile rubber (NBR), carbon black and other additives with cross-linked sodium polyacrylate (CSP), which was modified by interpenetrating polymer network technology with cross-linked P(AA-co-BA). The structure of WSR was characterised by SEM. The mechanical properties, water swelling ratio by mass and the percentage loss of CSP in the WSR were investigated. The results showed that the modified CSP grains can be dispersed well in the NBR and that it resulted in increase of mechanical properties and water swelling ratio and in decrease of percentage loss of CSP compared with the unmodified one. When the percentage content of cross-linked P(AA-co-BA) used to modify CSP reached 30%, the tensile strength, elongation at break and water swelling ratio of WSR exhibited a maximum value, and percentage loss of CSP exhibited a minimum value. When the content of CSP in WSR was 30 phr, the tensile strength, elongation at break, water swelling ratio and percentage loss of CSP of the WSR containing CSP modified were 11·3 MPa, 1943%, 532% and 5·8% respectively.

Preparation, water absorbent and mechanical properties of water swellable rubber

Water swellable rubber was prepared by blending styrene butadiene rubber as a matrix, cross-linked poly sodium polyacrylate (PAANa) as a high absorbent water resin, copolymer styrene maleic anhydride as a compatibiliser and polyethylene glycol as an absorbent accelerant. The preparation process was described. The effects of various preparation conditions, such as amount of sulphur, ratio of silicon dioxide to nanocalcium carbonate, amount of PAANa and amount of compatibiliser, on its water absorbency and mechanical properties were investigated by orthogonal tests. The optimal reaction conditions were 2 portion (phr) sulphur, 28∶12 silicon dioxide/nanocalcium carbonate, 60 phr PAANa and 5 phr compatibiliser. Furthermore, the vulcanisation property of the rubber was measured.