Ningxia Dadi PVA 2699

Ningxia Dadi PVA 2699 is a fully hydrolyzed polyvinyl alcohol resin whose grade code follows the conventional Chinese PVA nomenclature. The prefix 26 identifies a nominal degree of polymerization of 2600, and the suffix 99 identifies a nominal alcoholysis degree of 99.0 mol%. The resin is supplied as white to off-white granules or powder with bulk density commonly reported in the range of 0.40–0.60 g/cm³. It is intended for aqueous solution processing rather than direct melt extrusion; the as-received polymer is not melt-dispersible without plasticizer and controlled thermomechanical treatment. Dissolution requires hot water and shear, normally 85–95 °C, because the fully hydrolyzed acetate-to-alcohol conversion reduces cold-water affinity relative to partially hydrolyzed grades such as 2695. The combination of high molar mass and high hydrolysis degree raises solution viscosity, increases dry-film tensile strength, and reduces cold-water solubility relative to lower-DP or lower-hydrolysis PVA grades. Lot-specific release testing should be based on the supplier’s certificate of analysis; published data for Ningxia Dadi PVA 2699 as an independent grade is limited.

The representative grade-class specification matrix is shown below. Actual release limits are lot-specific and should be confirmed against the producer’s certificate of analysis.

Release limits for ash and volatile matter can vary with production campaign and packaging type. For applications requiring food-contact compliance, the formulator must verify the supplier’s compliance declaration against the target market regulation, such as EU 10/2011 or FDA 21 CFR 175.300, because the base resin grade alone does not establish finished-article compliance.

For solution make-down, the 4% viscosity range of 60–70 mPa·s is a grade-class reference; at 8% solids, the viscosity increases disproportionately because chain entanglement in the concentrated regime scales with concentration raised to a power greater than one. High-shear mixing equipment should therefore be selected with a low-shear impeller sweep and a high-shear rotor-stator zone to break up partially swollen granules without creating excessive mechanical shear that can reduce molar mass. The temperature ramp should not exceed 2 °C/min below 90 °C; too-rapid heating produces a viscous skin on the granule surface that encloses dry polymer and forms fisheyes. Once the solution reaches 95 °C, a hold time of 30–45 min under moderate agitation is common in open kettles, but jet cookers with high turbulence can achieve full dissolution in 15–20 min. Filtering the solution through 60–100 mesh before use is a practical control for undissolved gel specks. These operating windows are equipment-dependent; published data for this specific grade in all mixer geometries is limited.

What Distinguishes the 2699 Grade from Adjacent PVA Grades?

The nominal degree of polymerization 2600 places the product above PVA 1799, PVA 2099, and PVA 2499 in molar mass and solution viscosity. The fully hydrolyzed character remains close to PVA 1799 and PVA 2499, so the primary difference is rheological and film-strength related rather than alcoholysis related. A higher molar mass increases chain entanglement, which raises the 4% solution viscosity from approximately 25–31 mPa·s for PVA 1799 to 60–70 mPa·s for PVA 2699 under identical aqueous solution conditions. This increase permits lower use concentration in warp size and adhesive formulations, but it requires longer cooking time and more aggressive agitation. The comparative matrix below collates grade-class values commonly reported in technical data sheets; it is not a statement of equivalence across producers.

Published data for direct side-by-side comparison is limited; the table collates grade-class values commonly reported in technical data sheets rather than lot-specific release data. When Ningxia Dadi PVA 2699 is compared with a partially hydrolyzed 2695 grade, solubility and surface activity differ: 2699 requires higher dissolution temperature and yields films with higher water resistance, while 2695 hydrates more readily at lower temperature and is preferred where cold-water solubility or surface activity in emulsion polymerization dominates.

In cotton and polyester-cotton warp sizing, Ningxia Dadi PVA 2699 is cooked in a jet cooker or open kettle at 92–98 °C before delivery to the size box of a slasher. Size-box temperature is maintained at 85–90 °C to prevent surface skinning, and wet pick-up is controlled by squeeze-roll pressure of 8–12 kN/m across the warp width. At 4% solids, the grade yields a highly viscous solution with mild shear thinning; viscosity drift outside ±5% of the target value can shift add-on percentage and alter weaving efficiency. The high molar mass contributes to film toughness, but it also raises the minimum cooking temperature compared with PVA 1799, which must be considered when converting existing size-kitchen equipment from low-viscosity grades. Sized-yarn tensile retention is commonly assessed by ASTM D2256-22; abrasion resistance is evaluated on a loom or abrasion tester rather than by a single universal standard. Batch-to-batch viscosity variation is controlled by the supplier’s certificate of analysis, but mills operate under closed-loop size-box solids monitoring to compensate for evaporation and yarn water uptake. Overshooting the cook temperature above 98 °C for extended periods can induce polymer chain scission, which lowers size viscosity and weakens the sized yarn under high-speed weaving.

When High-Hydrolysis PVA Is Used in Emulsion Polymerization

In vinyl acetate and vinyl acetate-ethylene emulsion polymerization, PVA protective colloids are usually selected from partially hydrolyzed grades because their residual acetate groups increase surface activity and reduce aqueous solution viscosity at equivalent molar mass. Ningxia Dadi PVA 2699 can be used when the dried adhesive film requires high water resistance or when the formulation can tolerate higher cook temperature and higher reactor viscosity. The polymer is dissolved in the water phase at 90–95 °C before radical initiation; insoluble gel particles must be removed by filtration through 80–120 mesh stainless steel screens to avoid seed instability. The high degree of hydrolysis increases the onset temperature of phase separation relative to partially hydrolyzed grades, and the solution must be held above 60–70 °C during transfer to prevent gelation. Reactor viscosity during polymerization may rise more rapidly than with 2695; published data for this specific configuration is limited, so pilot-scale evaluation is required before full production. Residual salt content, particularly sodium acetate from hydrolysis, can interact with ionic initiators and should be tracked against the certificate of analysis limit when reactor reproducibility shifts.

In packaging and paper-converting adhesives, Ningxia Dadi PVA 2699 is formulated with plasticizers such as glycerol or sorbitol, defoamer, and preservative to produce remoistenable or water-activated adhesive layers. A typical high-shear dispersion step uses a sawtooth dissolver with tip speed of 10–15 m/s at 80–90 °C; polymer is added slowly under vortex to prevent fish-eye formation. The high viscosity of the 4% solution supports adhesive film build on coaters running at 30–80 m/min, depending on rod or roll coating configuration. The fully hydrolyzed grade has limited solubility in alcohol-rich solvent blends; formulators should keep ethanol content below the point of polymer precipitation and avoid combination with borate ions, which can induce viscosity spikes and gelation through diol-borate complexation. Open time and set speed depend more on substrate absorptivity and plasticizer level than on polymer viscosity; formulation-specific testing per TAPPI T 441 om-20 for water resistance is required when moisture contact is specified. For remoistenable grades, dried film block resistance is affected by equilibrium moisture uptake above 60% RH, and storage in sealed polyethylene-lined sacks is recommended for the as-supplied resin.

Film Mechanical Properties and Plasticizer Migration Boundaries

Cast films from Ningxia Dadi PVA 2699 are evaluated after conditioning at 23 °C and 50% RH because moisture acts as a plasticizer and reduces tensile strength. Film tensile properties are measured according to ISO 527-3; the fully hydrolyzed backbone increases crystallinity and reduces equilibrium moisture regain relative to partially hydrolyzed grades, but the exact tensile modulus depends on drying temperature, draw ratio, and plasticizer content. Glycerol addition at 10–20 wt% lowers the glass transition and improves flexibility, but migration of plasticizer to the film surface can occur at relative humidity above 60%, changing surface tack and seal behavior. For water-soluble packaging applications, this grade dissolves slowly at 20–30 °C and more rapidly above 70 °C; if cold-water solubility is required, a partially hydrolyzed lower-DP grade should be substituted. The high crystallinity of the dried film also limits heat-seal initiation temperature and may require the addition of lower-hydrolysis PVA or polyethylene glycol to widen the seal window. Thickness control below 25–30 µm is critical when the film is used as an interleaving layer because uneven caliper creates local stress concentration during transverse stretching.

Surface sizing on a film press or rod metering size press uses Ningxia Dadi PVA 2699 at dry pick-up of 2–6 g/m² to improve surface strength, oil-holdout, and print quality on packaging grades and release base papers. The size solution is cooked separately and blended with oxidized starch at 10%–30% PVA on starch dry basis; continuous Brookfield or Viskomat viscosity measurement at 50 °C is used to maintain constant film-press transfer. High molar mass increases film-forming capability but also raises size-press misting at machine speeds above 1200 m/min; equipment with enclosed nip and mist extraction is preferable. The product’s fully hydrolyzed nature reduces rewetting and helps meet oil-holdout requirements measured by TAPPI T 559 or ISO 16532-1 for grease resistance. Overdosing above the starch compatibility limit can produce film splitting and rod streaks; a jar test at target solids and temperature is a standard pre-run control. Addition of a defoamer is often required because high-viscosity size solutions entrain air during return-flow pumping, and entrained air reduces size-press metering uniformity.

Thermal Degradation in Alkaline Size Formulations Follows a pH-Dependent Pathway

In alkaline textile or paper formulations, PVA 2699 is sensitive to chromophore-forming degradation reactions when the size-kitchen pH exceeds 9 and the cook temperature remains above 95 °C for more than 2–3 h. The fully hydrolyzed backbone can undergo chain scission and oxidation at the secondary alcohol positions, producing conjugated unsaturation and a yellow-brown tint. The degradation rate is influenced by dissolved oxygen, alkali concentration, and the presence of starch or reducing sugars; closed cookers with nitrogen blanketing and temperature control below 95 °C reduce viscosity loss. Because the 2699 grade has a higher initial viscosity, the relative viscosity loss after thermal aging is more visible than in lower-DP grades. Processors using caustic starch thinning should avoid simultaneous PVA addition until the starch slurry is neutralized or cooled, as the combination of high pH and high temperature accelerates polymer degradation. If the final size film exhibits discoloration, the fault is commonly traced to alkali over-addition rather than to the PVA resin itself.

Storage of Ningxia Dadi PVA 2699 should follow closed-warehouse conditions at 5–35 °C and relative humidity below 60% RH. The resin is hygroscopic; moisture uptake increases caking tendency and can reduce the accuracy of gravimetric dosing. The product is not classified as a hazardous substance under GHS in the supplier’s safety data sheet, but airborne dust can form combustible dust clouds. Handling systems should use conductive grounding and dust extraction designed for organic particulate, with an ignition source excluded from the vicinity of open bag unloading. Pallets should not be stacked more than the supplier’s specified layer count because granule compaction under load increases the proportion of fused agglomerates that require longer cook times. Where high-humidity ambient conditions exceed 60% RH, the resin should be kept in sealed polyethylene-lined sacks and conditioned before use only to the extent necessary to avoid static discharge.