CW40-718 Emulsão de VAE de alto etileno para flexibilidade e impermeabilização de baixa temperatura

Designated as a high-ethylene vinyl acetate-ethylene (VAE) copolymer dispersion, CW40-718 is supplied at a solids content of 55 ± 1 %, a Brookfield viscosity of 800–2 500 mPa·s (spindle 4, 20 rpm, 25 °C), and a pH range of 4.5–5.5. The polymer architecture incorporates an ethylene weight fraction exceeding 25 %, shifting the glass transition temperature to approximately –25 °C and yielding a minimum film formation temperature (MFFT) below 0 °C without external coalescents. Protected with a surfactant system free of alkylphenol ethoxylates (APEO), the emulsion forms translucent, low-tack films that absorb less than 5 % water after 24-hour immersion per ASTM D570, a direct consequence of the hydrophobic polyethylene-like segments in the backbone. In comparison to standard VAE grades with ethylene contents around 10–18 %, CW40-718 eliminates the need for high-boiling coalescing agents in cold-weather application, reduces water sensitivity in cured films, and retains more than 300 % elongation at –20 °C without migrating plasticizers.

Production-scale trials on reverse-roll and knife-over-roll coating lines have identified a processing window between 15 °C and 35 °C ambient temperature; rheology modifiers based on hydrophobically modified ethoxylated urethane (HEUR) or high-molecular-weight cellulose ethers are recommended to raise low-shear viscosity above 3 000 mPa·s for vertical holdout. Drying profiles should ramp from 40 °C to 90 °C over a residence time of 3–5 min to avoid surface skinning, which traps residual water and creates micro-blisters visible under 10× magnification. At relative humidity above 60 %, forced-air velocity must exceed 2 m/s to maintain a dew point margin of at least 5 °C below the film surface temperature. Typical line speeds of 8–15 m/min on a 2 m wide polyester nonwoven carrier produce dry coat weights of 100–250 g/m² for single-component flexible waterproofing membranes meeting the crack-bridging requirements of EN 14891:2017 at –10 °C.

When Does Low-Temperature Elasticity Surpass Conventional VAE and Acrylic Dispersions?

Systematic comparison of CW40-718 against a commercial VAE with 15 % ethylene (Std-VAE) and a styrene-acrylic copolymer (SA) designed for waterproofing coatings reveals a crossover in elastic performance at sub-zero temperatures that alters material selection criteria for cold-climate applications. The table below summarizes key property differences.

The 80–120 % elongation of Std-VAE at –20 °C is typically insufficient for crack-bridging applications under EN 14891 Class A4 (≥ 0.5 mm bridging at –10 °C), whereas CW40-718 achieves this without plasticizer addition. Plasticizer-free films avoids the well-documented embrittlement that occurs in external plasticized systems when dibutyl phthalate or benzoate esters migrate into the substrate over 6–12 months of service, as evidenced by thermomechanical analysis (TMA) with a penetration probe.

When formulating two-component cementitious flexible slurries, the high-ethylene VAE contributes to retarding portland cement hydration as indicated by isothermal calorimetry data; a retardation of initial set by 60–90 min is observed at 20 % polymer-cement ratio (p/c) compared to unmodified paste. This necessitates the addition of 0.05–0.15 % (by cement weight) of calcium formate or lithium carbonate accelerator to restore a final setting time below 6 h at 5 °C. Field experience on multi-story residential façade waterproofing has shown that omission of the accelerator leads to washout of the slurry under light rain when applied at thicknesses above 2 mm, because the surface remains water-sensitive beyond 8 h.

What Limits Film Clarity and Block Resistance in High-Ethylene VAE without Coalescents?

CM40-718 forms a coalescent-free continuous film at 0 °C, but this is coupled with a reduction in surface hardness—König pendulum damping time measured per ISO 1522 falls below 20 s for an unpigmented film, compared to 45–55 s for a 15 % ethylene VAE film formed with 3 % Texanol on total binder. The low Tg produces a tacky surface at ambient temperatures above 30 °C when applied without matting agents. In clear wood coatings or high-gloss waterproofing topcoats, this leads to dust pickup values exceeding 50 mg/cm² in the ASTM D3719 dirt pickup test after one week outdoor exposure in a suburban environment. To counteract excessive tack, formulators incorporate 2–5 wt% (on binder solids) of a high-Tg polyurethane dispersion or a silane-functional acrylic that undergoes moisture-triggered crosslinking during drying, raising the composite Tg to approximately –5 °C without sacrificing low-temperature crack bridging.

Dispersion of CW40-718 with high-speed dissolvers equipped with Ø 250 mm cowles blades at tip speeds above 12 m/s generates macro-shear that can break the protective colloid layer and cause microscopic coagulum formation if the temperature exceeds 40 °C. Processing recommendations derived from scale-up at 500 L batches in a planetary disperser include a pre-mix phase of 10 min at 200 rpm before filler addition, followed by gradual increase to 800 rpm under water jacket cooling to maintain temperature below 35 °C. Filler loadings up to 45 wt% calcium carbonate (d₅₀ 5 µm) yield stable, non-sedimenting pastes with Stormer viscosity of 90–110 KU, suitable for trowel application in basement waterproofing.

Mixing CW40-718 with amine-functional silane adhesion promoters or certain polyaziridine crosslinkers must be avoided; the slightly acidic pH (4.5–5.5) protonates amine groups and triggers premature gelation within the dispersion. This incompatibility was observed in a pilot compound for concrete repair mortar where addition of 0.3 wt% γ-aminopropyltriethoxysilane led to a viscosity spike from 2 500 mPa·s to over 50 000 mPa·s within 15 min of agitation. Epoxy-functional silanes, in contrast, remain stable for a pot life exceeding 4 h and provide equivalent wet adhesion improvement.

In roofing adhesive formulations subjected to cyclic temperature fluctuations from –30 °C to +80 °C, the high-ethylene VAE retains its flexibility but exhibits a drop in tensile strength to 2.5–3.5 MPa at +80 °C (measured by dynamic mechanical analysis at 1 Hz). For substrates with high thermal expansion coefficients such as polycarbonate sheets, this softening reduces the shear strength at the overlap joint below 0.2 MPa as measured by EN 1465, posing a risk of cohesive failure. Reinforcement through blending with 10–20 % hydrophobically modified polyvinyl alcohol or a hard VAE (Tg +10 °C) is practiced to lift the service temperature window.

Storage Stability and Microbial Susceptibility in Plant Conditions

CW40-718 is biostabilized with a combination of benzisothiazolinone (BIT) and methylisothiazolinone (MIT) to satisfy the EU Biocidal Products Regulation (BPR) and maintains a shelf life of 12 months when stored in sealed HDPE totes at 5–30 °C. Bulk storage in 10 000 L stainless steel tanks must be agitated slowly (20 rpm, anchor stirrer) every 48 h to prevent syneresis. Freeze-thaw stability is limited: more than one cycle of freezing to –5 °C results in irreversible coagulation; tank heating systems must be interlocked to maintain a setpoint of 10 °C during winter transport. Plant audits have reported that exposure of an opened tote to ambient air for longer than 14 days in high-humidity warehouses (RH >85 %) led to surface skinning and the growth of Aspergillus niger on the dried skin, even though the liquid phase retained active biocide. Overhead covers and nitrogen blanketing are effective countermeasures.