Waterborne Polyurethane Dispersions Research Articles

Preparation of Waterborne Polyurethane-Based Macroporous Sponges as Wound Dressings.

Recently, eco-friendly and biologically harmless products of waterborne polyurethane (WPU) instead of solvent-borne polyurethane have been strongly progressed in both industries and research areas. Accordingly, we developed a WPU-based macroporous sponge as a skin tissue engineering matrix. Also, the WPU dispersion in water was modified by using a foaming agent in order to create creamy emulsion resulting in enlarging surface area wherein cells could adhere, grow, and proliferate. We investigated the effect of a foaming agent on the morphology of surface and internal structure, wettability. In vitro studies also confirmed enhanced adherence and proliferation of cells with increased metabolic rate. These results proved that the use of foaming agent could alter the internal structure, surface property, and biocompatibility.

Synthesis and properties of waterborne polyurethane dispersions for surface coatings on poly(vinyl chloride)

Recently, conventional solvent-typed polyurethanes are subject to many regulations due to emission of organic volatile compounds(VOCs) and researches have been focused on eco-friendly waterborne polyurethane dispersions(WPUDs) as an alternative of conventional solvent-typed ones causing poor working environment. PVC is widely used because of low price and good heat and fire resistance. To develop eco-friendly coatings on poly(vinyl chloride) (PVC), various WPUDs were synthesized by combination of polyol such as polyester, polycaprolactone, polyether or polycarbonate, hydrophilic compounds (dimethylol butanoic acid, DMBA), and reactive silicone. The structure and properties of synthesized WPUDs were characterized by FT-IR, particle size, contact angle, surface energy, tensile strength, elongation, and adhesion strength. Also, their particle sizes decreased while tensile strengths increased with increasing DMBA content. Surface energy and contact angle of WPUDs were strongly affected by the content of hydrophobic reactive silicone. The optimum properties of WPUDs were obtained by controlling their compositions, polyol, hydrophilic compound, and reactive silicone.

A highly-effective ionic liquid flame retardant towards fire-safety waterborne polyurethane (WPU) with excellent comprehensive performance

The flame-retardant waterborne polyurethane (WPU) has attracted more and more attentions from academia and industry. However, the addition of conventional flame retardants into WPU will damage the emulsion stability and introduce the potential further risk to demulsification and preparation failure. In this work, a novel flame-retardant approach is proposed, demonstrating outstanding efficiency, excellent compatibility and minimized side effect. A water-soluble ionic liquid 1-methyl-3-((6-oxidodibenzo[c,e] (Akindoyo et al., 2016; Chattopadhyay and Raju, 2007) [1,2]oxaphosphinin-6-yl)methyl)-1-H-imidazol-3-ium-4-methylbenzenesulfonate ([Dmim]Tos) is applied as the additive flame retardant for the WPU dispersions. The resulting WPUs (WPU/[Dmim]Toses) display excellent flame retardancy via a low loading content (max 6.0 wt%) and potential adhesion applicable to industries, while maintaining the major comprehensive performance, including storage stability, mechanical property, thermal stability, transparency, hydrophobicity, etc. Effort from this work, besides of overcoming the explicit drawback, also serves as reference of novel methodologies to solve the compatibility issue between additive agents and WPU.

Synthesis and molecular interaction of tung oil‐based anionic waterborne polyurethane dispersion

AbstractIn the present work, four types of anionic waterborne polyurethane dispersions (APUD) based on polytetramethylene ether glycol (PTMG) and two aliphatic diisocyanates, dicyclohexylmethane diisocyanate (HMDI) or isophorone diisocyanate (IPDI), were prepared by polymerization methods which for the first time controlled the location (soft or hard segment) of hydroxylated tung oil (HTO) incorporation into the final APUD. The resulting HTO‐containing APUD polymers (HTO‐APUDs) with postpolymerization crosslinking capability were characterized using FTIR, DMA, AFM and water imbibition methods, and compared to model compounds synthesized to have the same parts of chemical structural linkages for band assignment. A common PUD sample, as well as polypropylene oxide (PPG) with molecular weight similar to HTO (Mn = 400), was used to replace it for preparing control samples to highlight the role of long branched chains and conjugated double bonds in HTO. Based on the analysis of multiple H‐bond interactions, the relationship of HTO location in the APUD polymer structure to the soft/hard segment compatibility and the diisocyanate structure was further studied. This work is expected to provide basic data for properties regulation in practical applications by adjusting the chain and phase structure, as well as the intermolecular interactions, in these APUDs.

Improving water resistance of waterborne polyurethane coating with high transparency and good mechanical properties

Polyester based waterborne polyurethane (WPU) dispersions modified with hydroxypropyl-terminated polydimethylsiloxane (HPDMS) and sulfonate polyester diol were synthesized. The water resistance of WPU coating improved significantly when 5% HPDMS was used for modification, but it also leads to the decreasing of dispersion stability and damages in the mechanical properties and transparency of WPU coating. It was found that incorporating ionic groups in soft segments (sulfonate polyester diol) of WPU can obtain a coating with good water resistance where only 0.5% HPDMS is needed. In this case, the water swelling of WPU coating decreased to 7.0% while the pure WPU was 15.2%. Meanwhile, the mechanical and optical properties of modified coating change slightly. Its tensile strength was 62.6 MPa, and its light transmittance at 532 nm was 83.8%. Zeta potential test indicated the introduction of sulfonate polyester diol could improve the stability of WPU dispersions. The water resistance improvement of the WPU coating could be ascribe to the decrease of surface free energy and the change of phase separation degree. The water swelling, X-ray photoelectron spectroscopy, and contact angle test results demonstrated the migration of HPDMS and sulfonate polyester diol segments on the coating surface. The phase separation of WPU coatings was measured by dynamic thermomechanical analysis. The modified WPU with excellent water resistance is promising in the application of transparent coatings.

Synthesis and Characterization of Environmentally-Friendly Self-Matting Waterborne Polyurethane Coatings

A series of self-matting waterborne polyurethanes (WPUs) were successfully prepared by introducing hydrophilic units into both soft and hard segments. By employing a polycaprolactone polyol containing carboxylate groups within the polymer chains to provide hydrophilicity directly, the matting performance of WPU films was greatly improved. The chemical structures of the WPU resins were confirmed by FTIR spectroscopy, and the morphology of WPU films was observed by SEM. The parameters of WPU preparation were investigated in detail. It was found that the surface gloss of WPU films as well as the particle sizes of WPU dispersions were closely associated with the content of hydrophilic units. As the content of carboxylates or sulfonates increased, the particle sizes of WPU decreased, while the gloss increased gradually. When the particle sizes of dispersions were greater than 3 μm, the gloss of WPU films coated on a leather surface was lower than 1. The results of TG showed that, the initial decomposition temperatures of WPU films were higher than 280 °C, which indicated these films also had good thermal stability. The prepared self-matting WPU coatings would have potential application prospects in the field of leather finishing.

Effect of different carboxylic acid group contents on microstructure and properties of waterborne polyurethane dispersions

The waterborne polyurethane (WPU) with different carboxylic acid group contents were prepared by a prepolymer method, adopting polycarbonate diol (PCDL) as soft segments and isophorone diisocyanate (IPDI) as hard segments. The different amounts of 2,2-dimethylolbutyric acid (DMPA) as hydrophilic chain extender were introduced into polyurethane molecular for studying the effect on microstructure and properties. The solid content, pH value and viscosity measurement were used to characterize the performance of WPU emulsion. The fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water contact angle tester and mechanical testing machine were utilized to measure the structure, crystallization performance, thermal stability, low temperature flexibility, wetting performance and mechanical properties of WPU films, respectively. The test value of impact, adhesive, flexibility and pencil hardness on tinplate of WPU coatings were obtained for observing film properties. The results indicated that the emulsification effect increase with the increased DMPA contents. The decomposition temperature of WPU films perform a slight decrease and the WPU films have excellence low temperature flexibility with the increased DMPA contents. The hydrophilic property of WPU films mainly are about 80°and the tensile strength value of 7 wt% WPU reaches 45 MPa and elongation at break at 420%.

Effect of DMPA Content on Colloidal Stability of Jatropha Oil-based waterborne Polyurethane Dispersion

Driven by the increase of oil price in the market as well as environmental concerns by the society, a renewable raw material such as vegetable oil becomes the alternative to produce bio-based polyol to replace non-renewable polyols in polyurethane production. The recent development of aqueous polyurethane dispersion proves that environmentally waterborne PUD offers an efficient alternative to the solvent-borne PUD for the application in ink, adhesives, and coatings. In this study, the jatropha oil has been successfully functionalized to polyol (JOL) by epoxidation and oxirane ring opening steps. Jatropha oil-based waterborne polyurethane (JPU) dispersions were produced by polymerizing the JOL with isophorone diisocyanate (IPDI) and dimethylolpropionic acid (DMPA). The colloidal stability of JPU dispersions was studied in terms of particle size and zeta potential. Varying DMPA content from 5.0-7.0 wt.% resulted in small average particle size of dispersion from 39.40 nm to 133.2 nm. High zeta potential obtained in a range of -52 mV to -65 mV indicates the particles in the dispersion are sufficiently separated and therefore stable. Eventually, the study provides an overview of vegetable oil-based waterborne polyurethane dispersion with good stability for surface coating application.

Bio-based waterborne polyurethanes reinforced with cellulose nanocrystals as coating films

In this study, two different bio-based waterborne polyurethanes (WBPUs) that use castor oil and tartaric acid in their formulations were modified by the incorporation of a renewable reinforcement, cellulose nanocrystals (CNC), to be further applied as metal coatings of tailored properties. Different mixed suspensions were prepared by blending aqueous suspensions of CNC with the WBPU dispersions to achieve CNC concentrations of 5 wt. % and 10 wt. % (dry basis). The viscosities of the mixed suspensions were adjusted, so that they could be used in dip-coating of aluminum plates, used as substrates. The coatings were tested using macroscopic methods such as knife and tape tests and contact angle. Microscopic techniques such as nanoindentation, nanoscratch and nanowear were carried out. The results showed the feasibility of using these nanocomposite WBPUs as coatings and the utility of the microscopic techniques in the characterization of the resulting surfaces.

New Waterborne Polyurethane-Urea Synthesized with Ether-Carbonate Copolymer and Amino-Alcohol Chain Extenders with Tailored Pressure-Sensitive Adhesion Properties.

New waterborne polyurethane-urea dispersions with adequate adhesion and cohesion properties have been synthesized by reacting isophorone diisocyanate, copolymer of ether and carbonate diol polyol and three amino-alcohols with different number of OH groups chain extenders using the prepolymer method. The waterborne polyurethane-urea dispersions were characterized by pH, particle-size distribution, and viscosity, and the polyurethane-urea films were characterized by attenuated total reflectance infrared (ATR-IR) spectroscopy, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and plate-plate rheology (temperature and frequency sweeps). Polyurethane-urea pressure-sensitive adhesives (PUU PSAs) were prepared by placing the waterborne polyurethane dispersions on polyethylene terephthalate (PET) films and they were characterized at 25 °C by creep test, tack and 180° peel test. The waterborne polyurethane-urea dispersions showed mean particle sizes between 51 and 78 nm and viscosities in the range of 58–133 mPa·s. The polyurethane-urea films showed glass transition temperatures (Tgs) lower than −64 °C, and they showed a cross of the storage and loss moduli between −8 and 68 °C depending on the number of OH groups in the amino-alcohol chain extender. Different types of PUU PSAs (removable, high shear) were obtained by changing the number of OH groups in the amino-alcohol chain extender. The tack at 25 °C of the PUU PSAs varied between 488 and 1807 kPa and the 180° peel strength values ranged between 0.4 and 6.4 N/cm, and their holding times were between 2 min and 5 days. The new PUU PSAs made with amino-alcohol chain extender seemed very promising for designing environmentally friendly waterborne PSAs with high tack and improved cohesion and adhesion property.

The Puncture and Water Resistance of Polyurethane- Impregnated Fabrics after UV Weathering.

Polyurethane is a polymer adaptable to different scientific and industrial requirements; nevertheless it is also extremely susceptible to UV radiation, which compromises the physical and mechanical functionality. In this framework, our study investigated the effect of waterborne polyurethane dispersion (WPUD) applied to a polyester (PET)-based fabric, through the impregnation method, on the puncturing and water resistance of the pristine material, before and after UV weathering. Results confirmed an increment of both features in the prepared fabrics, attributed to the PUR textile treatment; but a partially loss of the gained properties in the samples due to the UV weathering. In order to improve the efficiency of the impregnating dispersions, in protecting the durability of the treated materials, the addition of different UV light stabilizers, or/and of crosslinking agent into WPUD was also tested. From the experimental data, it can be concluded that formulations based on WPUD, containing both the crosslinker and UV organic absorber, have displayed an increment of their perforation and water resistance for the treated samples with respect to the starting textile, and contemporary have preserved the features against the UV light. Finally, microscopic and spectroscopic analyses have been performed as further characterization techniques of the samples surface.

Recyclable, remendable and healing polyurethane/acrylic coatings from UV curable waterborne dispersions containing Diels-Alder moieties

The aim of the present work is to increase the sustainability of UV curable waterborne polyurethane dispersions using the Diels-Alder chemistry. In this way, the obtaining of crosslinked polyurethane coatings presenting healing and recycling properties is proposed.Thus, waterborne polyurethanes were obtained by the acetone process replacing the chain extender by a diol containing the Diels Alder adduct and using acrylic chain ends that allowed the UV cross-linking. Photo-DSC results showed that the Diels Alder adduct did not prevent the UV cross-linking of the coating. In addition, FTIR, DSC and rheological experiments confirmed the occurrence of the DA and retro DA reaction (at 60 °C and 120 °C respectively) in the cross-linked polymer. Thanks to this reaction, the materials obtained by this methodology could be healed and reprocessed when increasing the temperature as shown by the maintenance of the mechanical properties and carbon dioxide permeability after repairing. These results can be of great interest towards the development of more sustainable waterborne polyurethane coatings.

Cationic graphene oxide nanosheets intercalated with polyaniline nanofibers: A promising candidate for simultaneous anticorrosion, antistatic, and antibacterial applications

Development of a coating with simultaneous anticorrosion, antistatic, and antibacterial properties is an important issue which has gained attention from both academic and industrial societies. Multifunctional Polyaniline /cationic reduced graphene oxide (P-RGO+) nanohybrid has been synthesized to induce these properties in waterborne polyurethane (WPU) coatings. The cationic reduced graphene oxide nanosheets (RGO+) were obtained through the in-situ reduction and functionalization with Dimethylformamide (DMF). The cationic reduced graphene oxide nanosheets were intercalated with Polyaniline nanofibers (PANI) to prepare a binary nanohybrid (P-RGO+). This nanohybrid was characterized through the FTIR, XRD, FESEM, and zeta potential techniques and its effect on anticorrosion, antistatic, antibacterial, and mechanical properties of the waterborne polyurethane coatings was studied. The results of Tafel and EIS plots exhibited that the modified coatings have an improved performance in term of protecting steel substrates against corrosion. Moreover, in the presence of the nanohybrid, the electrical surface resistance of the obtained coating reduced to reach 9.8 × 10+6 Ω/sq so that it can be counted as an antistatic coating. Moreover, utilizing P-RGO+ nanohybrid in the WPU dispersion not only improved antibacterial activity against both gram positive and gram negative bacteria but also caused the enhanced mechanical properties of the modified coating compared with the pristine coating.

The effect of silica/polyurethane waterborne dispersion on the perforating features of impregnated polypropylene-based fabric

In an attempt to improve the puncturing behavior of a commercial technical textile, this study investigated the effects of fabric impregnation with waterborne polyurethane dispersions (WPUDs). The infusing solutions were prepared by mixing a commercially available WPUD with other components, such as water, hydrophilic and hydrophobic silica (SiO2) nanoparticles, and a crosslinker. Quasi-static perforation tests were performed on a dynamometer machine equipped with a spherical spike and pointed blade as piercing probes. The results showed that the polyurethane impregnation augmented the puncture performances of the treated textiles. Then, further improvements in the spike and blade strength of the impregnated fabrics were obtained by adding hydrophilic silica nanoparticles and crosslinker into WPUDs, respectively. No effect of silica functionalization (hydrophilic or hydrophobic) has been verified on the mechanical features of the respective treated samples for the tested filler contents of 3% and 5% in wt. The best fabric features (blade strength increase of +63% and puncture strength increase of +71% compared to the neat material) were obtained by combining the two additives, nano SiO2 and crosslinker, into the polyurethane. The performances of these last systems were also superior to those obtained by doubling the amount of polymeric dispersion applied to the neat materials. The discussion of the results was supported by electron scanning microscopy, infrared spectroscopy, and further measurements of the cutting resistance. Finally, the mass per unit area of the substrate for the impregnated samples was measured in order to assess weight gain due to treatment.

Ionizable polyol from cottonseed oil for anionic waterborne polyurethane-silanol dispersions

A novel cottonseed oil-based ionizable polyol was introduced as ionic soft segment in waterborne polyurethane dispersion (PUD) synthesis. The ionizable polyol was synthesized by ring opening of epoxidized cottonseed oil (ECSO) with 4-aminobenzoic acid (PABA) and blended with hydroxylated cottonseed oil polyol (HCSO) in different weight ratios to develop a series of mixed polyols having different hydroxyl numbers viz., 146, 130 and 114 mg KOH/g. Three different PUDs were synthesized using the mixed polyols, isophorone diisocyanate, and 3-aminopropyltriethoxysilane. The chemical structure, thermo-mechanical properties, and surface properties of cured PUD films were examined using Fourier-transform infrared spectroscopy (FTIR), Dynamic mechanical thermal analysis (DMTA), universal testing machine (UTM) and contact angle measurements respectively. The effect of Si–O–Si cross-linking network density, which increases with an increase in OH values of the mixed polyol was also investigated. All the PUDs prepared in this study exhibited good storage stability (>4 months), and the average particle sizes of PUDs ranged from 18 to 124 nm. The highest hydroxyl mixed polyol derived PUD film (PUD-35 film) exhibited high thermal stability, mechanical strength; Tg value, water contact angle value, chemical, and abrasion resistance properties due to the extended siloxane cross-link network structure. The introduction of ionizable polyol into the soft segment led to an improvement in hard and soft segment phase mixing of PUDs, and this strategy could enrich the exploration of new synthetic methodologies in the field of bio-based PUD manufacturing.

Fabrication and Properties of Superhydrophobic Waterborne Polyurethane Composites with Micro-Rough Surface Structure Using Electrostatic Spraying.

Waterborne polyurethane (WPU) coatings hold advantages of good toughness, low cost and environmental protection. However, the low water contact angle (WCA), poor wear and corrosion resistance make them unsuitable for application in the superhydrophobic coatings such as antipollution flashover coatings for transmission lines, self-cleaning coatings for outdoor equipment and waterproof textiles. A series of superhydrophobic WPU composites (SHWPUCs) with micro-rough surface structure was prepared by electrostatic spraying nano-SiO2 particles on WPU composites with low surface energy. It showed that as the hydrophobic system content rose the WCAs of the composites first increased and then remained stationary; however, the adhesion and corrosion resistance first increased and then decreased. An appropriate addition of the hydrophobic system content would lead to a dense coating structure, but an excessive addition could increase the interfaces in the coating and then reduce the coating performance. When the mass ratio of the WPU dispersion, polytetrafluoroethylene (PTFE) particles and modified polydimethylsiloxane was 8:0.3:0.4, 10 g/m2 nano-SiO2 particles were sprayed on the uncured coating surface to construct the SHWPUC with a WCA of 156°. Compared with pure WPU coating, its adhesion and corrosion resistance increased by 12.5% and one order of magnitude, respectively; its wear rate decreased by 88.8%.

Study of waterborne polyurethane materials under aging treatments. Effect of the soft segment length

Coatings made of waterborne polyurethane dispersions are a promising alternative to solvent-borne ones but their mechanical and thermal properties under harsh outdoor conditions such as high temperature and humidity are somewhat limited. In this work saturated polyesters (PBA) with different molecular weights (800–2600 g/mol) were synthesized by reacting adipic acid with 1,4 butanediol. These polyols, an internal emulsifier, and an aliphatic diisocyanate were used as raw materials to synthesize polyurethane (PU) aqueous dispersions with solids contents of 29–38 wt%. The increase of the molecular weight of the polyol decreased the mean particle size of the PU dispersions from 308 to 78 nm.Polyurethane (PU) films were obtained by water evaporation of the PU dispersions and they were annealed at 80 °C for 2 h. Accelerated aging studies were performed by submerging the PU films in the water at 80 °C for 2 h. The PU films synthesized with the polyols with lower molecular weight exhibited enhanced phase miscibility, giving place to storage and loss moduli of similar magnitudes in a wide temperature range and they were less susceptible to hydrolytic degradation. Microphase miscibility was favored when shorter polyols are used. Contact angle measurement and cross-hatch adhesion test on PU coatings placed on stainless steel plate, before and after annealing and water aging were carried out. All PU coatings retained the adhesion to the substrate after aging, the PU coatings synthesized with shorter polyols exhibited enhanced adhesion.

A renewable and multifunctional eco-friendly coating from novel tung oil-based cationic waterborne polyurethane dispersions

Bio-based waterborne polyurethanes (WPUs) as a novel kind of economic and eco-friendly coating have attracted more attention in recent decades due to their sustainability, availability, and low toxicity advantages. In this work, a tung oil based polyol (TOP) is effectively fabricated without complicated purification process under a relative low reaction temperature, and subsequently used to prepare a series of cationic waterborne polyurethane dispersions (WPUDs) with different TOP contents. The effect of TOP content on the particle size, zeta potential and storage stability of WPUDs is detailly investigated by zeta-sizer and centrifugation measurement. The post-curing behavior of these cured films is tested by tracing the gel content. Thereafter, the WPUDs coating properties including mechanical properties, thermal resistance, hydrophobicity, morphology, pencil hardness, adhesion and solvent resistance are also carefully investigated which demonstrate that more introduction of TOP into the dispersions may help improve tensile strength, thermal stability, hydrophobic capability, phase compatibility, pencil hardness for the cured films. More importantly, antibacterial experiments demonstrate that these WPUDs dispersions exhibit well inhibition effect toward Escherichia coli and Staphylococcus aureus. This study may provide a reference for developing highly effective, renewable, multifunctional and eco-friendly coating.

Silver(I) complex with a Schiff base ligand extended waterborne polyurethane: A developed strategy to obtain a highly stable antibacterial dispersion impregnated with in situ formed silver nanoparticles

In this study, as a novel strategy to overcome gel formation and coagulation problem of waterborne polyurethane (WPU) dispersions containing silver ions, a Schiff base ligand (SBL) derived from 2,4-dihydroxybenzaldehyde and Bis(3-aminopropyl)amine was synthesized and utilized as chain extender in fabrication of WPUs. The effect of SBL incorporation into WPU chains and subsequent complex formation with Ag ions on the storage stability and particle size of the dispersions were studied. The UV–vis spectroscopy results of prepared dispersions confirmed the formation of Ag NPs within the WPUL/Ag sample through in situ reduction of Ag ions by PTMG (polytetramethylene glycol) polyol as a non-toxic reducing agent. Transmission electron microscopy (TEM) images of WPUL/Ag dispersion demonstrated that the formed Ag NPs exhibited a spherical shape with a size below 10 nm. Furthermore, X-ray diffraction (XRD) analysis of WPUL/Ag film affirmed the presence of Ag NPs within the WPUL matrix. Scanning electron microscopy (SEM) photographs of WPUL/Ag film also displayed a homogeneous dispersion for in situ formed Ag NPs. Antibacterial assays showed an excellent activity for WPUL/Ag film against S. aureus and P. aeruginosa bacteria. Besides, in vitro cytotoxicity studies confirmed that the WPUL/Ag sample possess a good biocompatibility toward L929 cells.

Synthesis and Properties of Waterborne Polyurethane Acrylates using Reactive Silicone

Since most of the coatings have been prepared by organic solvents, there are many regulations because of the environmental and health hazards caused by volatile organic compounds. As an alternative to organic solvent-based polyurethanes which are broadly used in coatings, waterborne polyurethane dispersions are receiving great attendance due to their harmless to humans and environment. In this study, water-dispersed UV-curable polyurethane acrylates were synthesized by varying content of reactive silicone which gives surface hydrophobic. The physical properties of the synthesized polyurethane acrylates were measured as a function of content of silicone. The molecular structure and physical properties of the synthesized water-dispersed UV-curable polyurethane acrylates were investigated by FT-IR and contact angle, surface energy, particle size, tensile strength, and elongation. The results showed that as the content of reactive silicone increased, the surface energy of the cured coating decreased due to hydrophobicity of silicone. The optimum physical properties were obtained by controlling content of reactive silicone.