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This thermoplastic characteristic provides several advantages for using SBCs in adhesive formulations: compounds can be obtained with excellent physical properties without vulcanization; adhesive compounds can be formulated by a thermal processing technology (hot-melt adhesives); and adhesives can be formulated by dissolving ingredients in organic solvents (solventborne adhesives). SBCs synthesized using solvent-based technology also offer narrower molecular weight distribution; this allows the polymers to dissolve directly into organic solvents without a pre-mastication process, such as those employed in the production of chloroprene rubber (CR), emulsion SBR, or natural rubber (NR) based adhesives.
Dynasol produces several SBCs with different structures and compositions for various market segment requirements (see Table 1).
SBCs in Solventborne AdhesivesSolventborne adhesive are mainly used in applications where higher cohesive strength is required, such as those found in the building and construction markets.
SBCs are widely used in solventborne adhesive formulations due to their advantages over other elastomeric structures. They develop faster solubility than other polymer bases, such as CR, NR, or emulsion SBR, without the need for additional processes (such as pre-mastication) due to their narrow molecular weight distributions. This, in turn, reduces operating costs and increases productivity. SBCs also develop lower solution viscosities, allowing formulators to increase the formulation’s solids content and reduce VOC evaporation levels. This leads to a decrease in solvent volume, as well as lower handling, transportation and storage costs.
Table 2 compares SBC-based solventborne formulations with a commercial 25%-solids CR-based adhesive. The first formula (F-01) was based on a radial medium-molecular-weight copolymer. The second (F-02) used a blend of a high-molecular-weight radial copolymer and a linear SBS containing 20% diblock. The third formula (F-03) was a CR commercial adhesive. All were applied using the same procedure and the same adhesive weight for the bond.
SBCs in Hot-Melt AdhesivesThe formulation and use of hot-melt adhesives offer a cost benefit and environmentally friendly option to adhesive manufacturers; they eliminate the drying process and, therefore, the equipment and energy requirements of solvent- or water-borne adhesives. In addition, organic solvents are not required, which reduces VOC emissions. Productivity is improved by reducing cooling time. SBCs can be easily formulated as hot-melt adhesives due to their thermoplastic nature, allowing them to melt by increasing the process temperature in order to incorporate all of the ingredients to obtain adhesive properties.
Table 3 shows a typical hot-melt adhesive formulation. An elastomeric base (SBC) was used to absorb debonding energy as elastic deformation and develop cohesive strength; a midblock tackifying resin was used to improve adhesion to different substrates; an endblock tackifying resin was used to reinforce styrenic domains cohesively; a plasticizer was used to modify polymer viscosity, thus improving adhesive wetting; and a stabilizer was used to extend the life of the ingredients.
Additives, such as viscosity modifiers and other non-reinforcing fillers, can be incorporated into the adhesive formulation to reduce cost, as well as to adjust rheological adhesive performance and other characteristics for improved productivity.
- Thermoplastic characteristics allow SBCs to be used in the formulation of either solventborne or hot-melt adhesives.
- The availability of products with different structures and compositions helps optimize performance according to the specific requirements of each application.
- SBCs can be used at a higher solids content than other polymers, such as CR and NR. They can achieve the same or better adhesive performance, thereby reducing VOC emissions and cost related to solvents use.
- New multi-arm structure copolymers offer improved adhesive performance over higher-styrene-content copolymers.
- S-SBR can be used as a substitute for SIS copolymer in adhesive formulations, improving properties such as shear and adhesive viscosity, and reducing formulation costs.