Celvolit 1426 VAE Emulsão

Celvolit 1426 is a carboxylated vinyl acetate-ethylene (VAE) copolymer emulsion supplied by Celanese as a ready-to-use aqueous dispersion with a typical solids content of 55 ± 1% by weight determined by ASTM D2369-22. The polymer architecture couples an ethylene content in the range of 17–20 wt% of the monomer feed with poly(vinyl acetate) blocks, yielding a glass transition temperature (Tg) near −15 °C (midpoint by differential scanning calorimetry, ISO 11357-2:2020). The intrinsic flexibility conferred by the ethylene segments reduces or eliminates the demand for external plasticizers in many adhesive formulations, minimising volatile organic compound (VOC) contributions and long-term migration risks. Within the Celvolit portfolio, grade 1426 occupies a mid-point between the lower-ethylene Celvolit 1400 (Tg ~+10 °C) and the ultra-high-ethylene Celvolit 1490 (Tg < −30 °C), delivering a balance of cohesive strength and low-temperature adhesion that is particularly suited for flexible packaging laminations, wood-veneer bonding, and wet-lamination of paperboard.

How Does the Ethylene Content in Celvolit 1426 Modify Polymer Chain Dynamics?

The incorporation of 17–20 wt% ethylene as random comonomer units interrupts the stereoregularity of the vinyl acetate sequences, suppressing crystallinity to less than 5% as estimated by wide-angle X-ray scattering. This internal plasticisation manifests in dynamic mechanical analysis as a pronounced drop in storage modulus beginning at −5 °C and a tan δ peak centred at −10 °C, characterising the glass transition. On a production-scale adhesive coated at 50 g/m² dry weight on a pilot reverse-roll coater (width 1.2 m, line speed 80 m/min), films dried above the minimum film formation temperature develop elongation at break exceeding 800% (microtensile test at 100 mm/min crosshead speed, ASTM D882-18). This extensibility translates directly into wet tack on fibrous substrates: when formulated with a glycerol rosin ester tackifier dispersion at 30% on binder solids, loop tack values on kraft paper reach 4.0–5.5 N/25 mm (TLMI Test L-IB2). In contrast, an all-acrylic dispersion of comparable Tg requires a significantly higher tackifier loading to achieve equivalent adhesion on board, and the acrylic system often suffers from plasticizer migration into the cellulose fibres over time, a phenomenon suppressed in VAE binders because the low Tg is permanently built into the backbone.

The minimum film formation temperature (MFFT) of neat Celvolit 1426 is reported at 0 °C (ASTM D2354). At drying temperatures below 5 °C, latex particles fail to coalesce into a continuous film without the addition of 2–5 wt% (on emulsion weight) of a high-boiling coalescent such as 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate. Incomplete coalescence yields micro-cracked films where peel adhesion on aluminium/polyester laminates drops by 30–45% (ASTM D903) and water resistance is compromised due to capillary wicking along crack boundaries. This constitutes a critical processing window: large-format gravure laminators operating at ambient conditions between 5 °C and 12 °C must actively pre-heat the web or the backing roll to > 15 °C, or else batch-to-batch bond-strength variability exceeding ±20% is frequently recorded.

Physical Property Specification and Standardized Test Methods

The values reflect production-scale batch averages from 10 m³ stirred-tank reactors equipped with pitched-blade impellers; tighter consignments are possible through end-use qualification protocols.

Formulated adhesive systems based on Celvolit 1426 are sensitive to pH-induced rheology control. Upon raising the system pH from the supplied 4.0–5.0 to 7.5–8.5 by gradual addition of dilute ammonium hydroxide or amino-functional silanes, ionisation of the backbone carboxyl groups drives a viscosity increase from approximately 2000 mPa·s to values exceeding 15 000 mPa·s. This alkali-swellable behaviour permits knife-over-roll and curtain coating application without external associative thickeners. On a high-speed packaging line filling 20 L pails via a double-diaphragm pump, however, a viscosity spike beyond 25 000 mPa·s has been observed to cause cavitation and intermittent flow. Inline monitoring with a Brookfield viscometer fitted with an SC4-27 spindle at > 100 s⁻¹ shear rate, combined with a pH-controlled dosing loop, is recommended to maintain viscosity within 12 000–18 000 mPa·s. Incompatibilities must be observed: addition of amine-containing hardeners such as polyfunctional aziridines or polyethylenimine causes instantaneous gelation through ionic crosslinking; polyvalent metal cations (e.g., Al³⁺ from aluminium sulfate) cause coagulation and grit formation. The emulsion is stabilised by a mixed anionic/nonionic surfactant system without poly(vinyl alcohol) colloid; therefore, borate ions do not induce the pre-gelation typical of PVOH-protected grades, but exposure to strong cationic surfactants results in irreversible flocculation. Storage must be kept between +5 °C and +40 °C; one freeze-thaw cycle destroys colloidal stability, and sustained storage above 45 °C accelerates hydrolysis of pendant acetate groups, liberating acetic acid and trace acetaldehyde, with a concomitant drift in pH and odour.

Equipment conditions also impose boundaries. During sustained roll-coating runs on a 2.5 m wide laminator at 120 m/min, the emulsion’s built-in defoamer package suppresses macro-foaming. Nevertheless, when the adhesive recirculation loop employs a centrifugal pump with a tip speed above 8 m/s, micro-bubble entrainment re-emerges, leading to pinhole defects in the adhesive layer. Installing a static mixer immediately downstream of the pump, and sizing the return line diameter to keep fluid velocity below 2.5 m/s, mitigates this effect. Coating head pressure fluctuations exceeding ±0.2 bar cause intermittent streaking, a failure mode linked to the emulsion’s shear-thinning index of 0.45–0.55 (power-law index between 10 s⁻¹ and 1000 s⁻¹, measured with a cone-and-plate rheometer, ISO 3219).

If Adhesion to Untreated Polypropylene Must Rival Solvent-Based Systems

The surface energy of neat polypropylene typically lies near 30 mN/m, well below the wetting threshold of aqueous VAE emulsions, which require a substrate surface energy above approximately 38 mN/m for spontaneous spreading. Without a corona pre-treatment raising the dyne level to at least 42 mN/m, peel strength of Celvolit 1426 on biaxially oriented polypropylene film does not exceed 0.5 N/25 mm (ASTM D3330). When blended with a water-borne chlorinated polyolefin adhesion promoter at 5% of binder solids, adhesion values can reach 1.8–2.5 N/25 mm following heat lamination at 80 °C, still falling short of solvent-borne polyurethane benchmarks (> 5 N/25 mm). This limitation defines the application envelope: Celvolit 1426 is engineered for high-energy substrates—wood, paper, aluminium foil, corona-treated polyolefins, and surface-oxidised polyester. Differences among grades in the Celvolit series are summarised below.

In practice, Celvolit 1426 is often selected over Celvolit 1425 when bondline flexibility must be maintained at sub-ambient temperatures encountered in refrigerated transport chains, while Celvolit 1475 is reserved for extreme flexibility at the cost of elevated surface tack and reduced shear resistance. 1426 retains a carboxyl functionality level that allows subsequent crosslinking with water-dispersible polyisocyanate or epoxy silane additives to improve heat resistance and solvent resistance, a route less effective in the high-ethylene 1475 due to its intrinsically low cohesive energy density. For formulations requiring compliance with indirect food contact regulations, the emulsion can be supplied in grades meeting FDA 21 CFR 175.105 and 176.170 compositional requirements, subject to end-use migration testing.