| HS Code | 335650 |
| Product Name | Ningxia Dadi PVA 2688 |
| Chemical Name | Polyvinyl Alcohol |
| Manufacturer | Ningxia Dadi Chemical Co., Ltd. |
| Grade | 2688 |
| Appearance | White granular or powder |
| Degree Of Hydrolysis | 86.0-89.0 mol% |
| Viscosity 4 Aqueous Solution 20 C | 50.0-60.0 mPa·s |
| Average Degree Of Polymerization | 2600 |
| Ph 4 Aqueous Solution | 5.0-7.0 |
| Volatile Content | ≤5.0% |
| Ash Content | ≤0.5% |
| Particle Size | 20-80 mesh |
| Water Solubility | Soluble in water with heating |
| Bulk Density | 0.4-0.6 g/cm³ |
As an accredited Ningxia Dadi PVA 2688 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Ningxia Dadi PVA 2688 is packaged in 25 kg multi-ply paper bags with an inner plastic liner for safe handling. |
| Container Loading (20′ FCL) | Description: Ningxia Dadi PVA 2688 is loaded into a 20-foot full container (FCL) in sealed bags, palletized, and securely braced. |
| Shipping | Ningxia Dadi PVA 2688 is shipped as a fine white powder in sealed, moisture-proof bags, cartons, or woven bags with liners. Keep dry, ventilated, and protected from humidity during transport. Non-hazardous, it ships as conventional cargo, though avoiding dust exposure during handling is recommended. |
| Storage | Store Ningxia Dadi PVA 2688 in a cool, dry, well-ventilated area, away from heat, open flames, and direct sunlight. Keep container tightly sealed to prevent moisture absorption, as polyvinyl alcohol is hygroscopic. Avoid dust accumulation and contact with oxidizing agents. Use appropriate personal protective equipment when handling. Under proper conditions, shelf life is typically two years. |
| Shelf Life | Shelf life is typically 12 months when stored in a cool, dry, sealed area away from moisture and direct sunlight. |
Ningxia Dadi PVA 2688 is a partially hydrolyzed polyvinyl alcohol grade with a nominal 4% aqueous viscosity of 45–55 mPa·s at 20°C and a saponification degree of 87.0–89.0 mol%. The following application profiles cover the grade’s established downstream segments where high molecular weight and controlled water sensitivity direct process design, formulation limits, and regulatory conformance.
Surface sizing of recycled white-top testliner and virgin kraft linerboard uses PVA 2688 as a high-molecular-weight co-binder with oxidized corn starch to raise surface strength and reduce linting on corrugating and printing lines. A typical size press working formulation contains 5–15 parts PVA 2688 per 100 parts oxidized starch on dry solids at a combined bath solids of 8–12 wt%; the polyvinyl alcohol is pre-dissolved separately at 10–15% solids in a jacketed cooker at 90–95°C, then blended into the starch solution at 65–70°C to avoid retrogressive viscosity drift. The metering system is a film press or puddle size press with rod or air-knife control, targeting a dry pick-up of 1.0–2.5 g/m² per side, after which the sheet is dried to 5.0–7.0% moisture. Compliance for food-contact paperboard rests on FDA 21 CFR 176.170 for aqueous and fatty foods, the EU Regulation (EC) 1935/2004 framework, and BfR Recommendation XXXVI for paper and board; surface strength is verified by Scott Bond TAPPI T 833 and edge wicking by TAPPI T 466. Terminal grades include high-performance corrugated medium and liner, recycled white-top testliner, gypsum board facing paper, and cupstock base sheets where the PVOH-starch film reduces porosity and improves print holdout. A documented mill bottleneck is viscosity instability if the PVA solution is discharged below 85°C into native starch; jacketed blend tanks are therefore specified for continuous delivery.
On cotton and polyester/cotton warps with high yarn hairiness, PVA 2688 is used in size formulations at 8–12% bath solids, where it commonly replaces 30–70% of modified starch dry solids. A production recipe for 40/1 Ne combed cotton warp uses 10 kg PVA 2688, 5 kg modified starch, and 1 kg acrylic size per 100 L of size liquor; the PVA is cooked separately at 90–95°C for 30–45 min before transfer to the size box maintained at 85–90°C. The slasher applies size at 30–60 m/min with a squeeze roll pressure of 8–15 kN/m, followed by cylinder drying at 100–130°C and moisture control to 6–8% residual on yarn. For textile compliance, the size must satisfy Oeko-Tex Standard 100 and ZDHC MRSL Version 3.1 when desizing effluent is assessed under REACH Annex XVII; yarn strength retention is measured by ISO 13934-1:2013, and hairiness reduction by ASTM D5647. Desizing is performed with amylase at 80–90°C and requires monitoring of COD in wash water because PVA 2688 is not readily biodegradable under anaerobic textile effluent conditions. Terminal products include rigid denim, poplin shirting, bed linen warp, workwear twill, and terry toweling where weaving efficiency depends on abrasion resistance at heald frames. A documented field failure on high-speed slashers is edge gel formation on size-box rolls when bath temperature falls below 85°C; recirculating jacketed size boxes are therefore used for temperature stability.
Vinyl acetate-ethylene and vinyl acetate homopolymer latices rely on partially hydrolyzed PVOH with 87.0–89.0 mol% hydrolysis to provide steric stabilization and control viscosity build during semi-batch polymerization. PVA 2688 is pre-dissolved at 10–15 wt% in demineralized water at 90–95°C, cooled to reactor temperature, and charged at 2–6 wt% based on total vinyl acetate monomer; for VAE grades, an emulsifier supplement of 0.5–2.0 wt% nonionic surfactant is used to adjust particle size. Polymerization proceeds in a jacketed stainless-steel reactor with an anchor impeller at 150–300 rpm, an ethylene pressure ramp of 20–80 bar, and a redox initiation system consisting of hydrogen peroxide and sodium formaldehyde sulfoxylate dosed over 3–5 h at 60–80°C. The resulting latex typically has a solids content of 50–55 wt%, a Brookfield viscosity of 3000–8000 mPa·s at 25°C measured per ISO 2555:2018, and a grit level below 0.05% on a 180 µm sieve. Regulatory anchor points for adhesive applications include FDA 21 CFR 175.105, FDA 21 CFR 176.170, and EN 204/205 D3/D4 wood adhesive classification; latex intended for packaging adhesives is assessed under EU 10/2011 if there is direct food contact. Terminal products include D3/D4 wood assembly adhesives, paper lamination and packaging adhesives, wallpaper and carpet-backing binders, and road-marking paint modifiers. A scale-up constraint with DP 2600 grades is the increase in latex viscosity when protective colloid feed exceeds 6 wt%; in reactors without external coolers, heat removal then becomes limiting and monomer feed must be slowed.
For dry-blended cementitious systems, the addition of PVA 2688 as a water-retention and green-strength additive is controlled at 0.3–1.0 wt% of the total dry mortar; the upper boundary of 1.5 wt% is not exceeded because high-DP PVOH can extend open time but reduce 28-day compressive strength when tested according to EN 1015-11:2019. Dry blending is performed in a horizontal ribbon or ploughshare mixer after the cellulose ether and redispersible polymer powder are premixed; mixing time is 3–5 min at 15–25°C and 40–60% RH to avoid moisture pickup. The dry powder is then mixed on site with water at 0.20–0.28 L/kg depending on the base formulation; PVA 2688 modifies rheology and reduces surface skinning before tile embedment. Compliance is anchored to EN 12004:2017 for C2TE/S1/S2 tile adhesives, EN 13813 for screed materials, EN 998-1:2016 for render, and CE marking under Construction Products Regulation (EU) 305/2011. Sag resistance, open time, and tensile adhesion after water immersion are tested according to the relevant annexes of EN 12004:2017; adhesion values for C2 classification must remain at or above 1.0 MPa after the specified conditioning cycles. Terminal products include C2TE/S1 cementitious tile adhesive, self-leveling underlayment, repair mortar, EIFS basecoat, and gypsum plaster. Borate-containing retarders must be avoided because reversible crosslinking between PVOH and borate can produce uncontrolled viscosity rise during batch mixing.
Partially hydrolyzed PVA 2688 is used as the high-strength fraction in cast water-soluble film for detergent unit-dose and agrochemical sachets; because an 88 mol% hydrolysis grade alone shows delayed cold-water dissolution, it is typically compounded with lower-hydrolysis or lower-DP PVOH grades, plasticizer, and surfactant rather than used as the sole resin. A cast-film formulation contains 70–85 wt% total PVOH resin of which PVA 2688 may be 20–50 wt% of the resin phase, with 8–15 phr glycerol or sorbitol plasticizer, 0.1–0.5% release agent, and residual moisture controlled at 6–10%. Film dissolution is tested by the time required for a 1 g sample to dissolve in 500 mL water at 25°C under 100 rpm stirring; film tensile performance is measured by ISO 527-3:2018 and water content by ISO 3251:2019. Regulatory compliance for detergent unit-dose packaging includes child-resistant packaging requirements under 16 CFR 1700 and the Detergents Regulation EC 648/2004; food-contact grade cast film for dry food sachets is assessed under FDA 21 CFR 177.1670 and EU Regulation 10/2011. The casting process requires deaerated 20–30 wt% aqueous PVA solution at 85–95°C delivered to a steel belt or drum dryer at 75–90°C; drying rate and winding tension are critical because residual moisture below 6% increases brittleness while moisture above 10% leads to blocking. Typical final film thickness is 50–80 µm, and hot-filling survival is influenced by plasticizer selection and seam seal geometry. Terminal products include laundry detergent unit-dose pouches, automatic dishwasher tablet wraps, agrochemical water-soluble sachets, and dye transfer inhibitor sheets.
In alumina and cordierite powder processing, PVA 2688 functions as a temporary organic binder that adsorbs onto ceramic particle surfaces and is burned out before sintering; the typical addition is 0.5–3.0 wt% of dry ceramic powder, dissolved into the slip as a 5–15 wt% aqueous solution at 90–95°C and mixed before spray drying. Spray drying is performed with inlet air at 180–220°C and outlet air at 90–110°C, yielding granules with 0.5–1.5% residual moisture and a target granule size of 50–250 µm. Green bodies are compacted on hydraulic or isostatic presses at 100–200 MPa; green strength is measured by three-point bending using ASTM C674, and dried piece density by ASTM C373-18. Compliance for electronic ceramic substrates is anchored to RoHS 2011/65/EU and REACH Annex XVII; binder burnout is conducted at 450–600°C in an oxidizing tunnel kiln with residual carbon controlled below 0.1 wt% as an industrial acceptance threshold. A documented production risk is overdosing PVA 2688 above 3.0 wt%, which raises slurry viscosity and creates hollow granules during spray drying; another is burnout above 600°C, where localized exothermic decomposition can crack thin-walled honeycomb bodies. Terminal products include alumina electronic substrates, cordierite honeycomb catalyst carriers, piezoelectric ceramic discs, and refractory kiln furniture.
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Ningxia Dadi PVA 2688 is a partially alcoholysed polyvinyl alcohol resin in the high-viscosity segment of the manufacturer’s alcoholysis series. The grade code separates into a nominal degree of polymerization of 2600 and a nominal alcoholysis degree of 88 mol%. Supplier certificates of analysis for the grade typically list a 4% aqueous solution viscosity of 44.0–52.0 mPa·s at 20 °C under GB/T 12010.3-2010, volatile matter not exceeding 5.0 wt%, ash not exceeding 0.5 wt%, and a pH of 5.0–7.0 in a 4% aqueous dispersion. The resin is supplied as white to off-white granules. Because the alcoholysis degree is intermediate, the material is classified as partially hydrolysed; because the chain length is high, it generates more viscous aqueous solutions than lower degree-of-polymerization grades such as PVA 2488 and dissolves more readily than fully hydrolysed PVA 1799.
The primary differentiating variable is molecular weight. In dilute aqueous solution, PVA 2688 exhibits higher solution viscosity than PVA 2488 at equal solids because the longer chain increases hydrodynamic radius and entanglement density. The residual acetate content of 12 mol% disrupts interchain crystallites and lowers the minimum dissolution temperature relative to PVA 1799, but the high degree of polymerization still requires controlled heating for complete solubilisation. Film tensile properties measured by GB/T 13022-1991 generally increase with degree of polymerization at constant alcoholysis degree, although direct quantitative comparison between 2688 and 2488 requires identical plasticizer content and conditioning at 23 °C and 50% relative humidity. Published data for the exact tensile increment of Ningxia Dadi 2688 over 2488 is limited; substitution trials should therefore include cast-film testing rather than relying solely on solution viscosity.
PVA 2688 belongs to the 26-series; the first two digits denote nominal degree of polymerization, and the final two digits denote nominal alcoholysis degree. The 88 mol% hydrolysis level is commonly selected for adhesives, sizing, and emulsion polymerization because it balances cold-water solubility with film water resistance. Fully hydrolysed 99 mol% grades require hot-water dissolution and are used where water resistance after drying is critical. Within the 88 mol% series, degree of polymerization is the main lever for solution viscosity and film strength.
Compared with PVA 1788, the 2688 grade has a longer chain and consequently higher aqueous viscosity at equivalent concentration. The practical difference is most visible in sizing and emulsion applications where the low-viscosity 1788 pumps more easily but contributes less film toughness, while 2688 increases machine load and wet pick-up. The substitution ratio is not linear; a direct equal-solids replacement can raise measured viscosity to an extent that depends on concentration, temperature, and shear rate. Published data for the exact shear-thinning index of Ningxia Dadi 2688 is limited, so pilot-scale viscosity measurement under the intended shear regime is required.
Dissolution behaviour is the main process constraint. The powder is best pre-slurried in cold water of 10–30 °C using a high-speed disperser at 500–800 rpm before steam heating to 85–95 °C. In a jacketed stainless-steel vessel with an anchor agitator running at 30–60 rpm, complete dissolution of an 8 wt% solids solution typically requires 45–60 min after the slurry reaches 90 °C. Above 10 wt% solids, vortex formation in unbaffled tanks can entrain air; a baffled vessel with low-shear impeller and vacuum degassing at −0.06 to −0.08 MPa reduces microbubble defects in subsequent film or size-press applications. The solution is shear-thinning, and the measured viscosity is dependent on spindle speed and thermal history, so the certificate value should be reproduced with the same rotational viscometer configuration before lot acceptance.
Production-scale dissolution failures usually originate from adding dry granules directly into hot water. The outer gel layer hydrates rapidly and prevents water penetration, producing semi-swollen fish-eye defects. Cold-water pre-dispersion at 10–30 °C minimizes this, and the powder should be added at a controlled rate that maintains visible surface turnover. The viscosity peak during dissolution occurs before complete solubilisation because swollen granules create transient high resistance; anchor agitator torque is typically highest around 60–70 °C before the granules fully dissolve. Monitoring torque rather than time provides a more reliable endpoint.
Typical certificate-of-analysis parameters for Ningxia Dadi PVA 2688 follow the supplier’s control ranges. The values below are representative ranges reported in technical literature for 26-series partially hydrolysed polyvinyl alcohol; they are not batch-specific guarantees.
| Parameter | Typical range | Test basis |
|---|---|---|
| Degree of polymerization, nominal | 2600 | Supplier grade designation |
| Alcoholysis degree | 87.0–89.0 mol% | GB/T 12010.2-2010 |
| Viscosity, 4% aqueous, 20 °C | 44.0–52.0 mPa·s | GB/T 12010.3-2010 |
| Volatile matter | ≤ 5.0 wt% | ISO 3251:2019 |
| Ash | ≤ 0.5 wt% | GB/T 12010.2-2010 |
| pH, 4% solution | 5.0–7.0 | GB/T 12010.2-2010 |
Ash and volatile matter are relevant for continuous gravimetric feeding. Moisture uptake at storage relative humidity above 60% can raise volatile matter beyond the certificate limit and reduce the exact polymer content delivered to a loss-in-weight feeder. If storage humidity exceeds 60%, drying at 60–80 °C for 2–4 h in a forced-air tray dryer restores the targeted solids content. Batch-to-batch variance in solution viscosity of ±3 mPa·s can shift wet pick-up in size-press operations; incoming material should be checked against the internal specification at 4% solids and 20 °C before formulation adjustment.
The certificate parameters do not include molecular weight distribution. Even when degree of polymerization is fixed at 2600, the breadth of the distribution can affect high-shear viscosity and film properties. Published data for the molecular-weight distribution of this specific grade is limited; requests for gel permeation chromatography data should be directed to the supplier when the resin is used in critical high-extension film or controlled-release applications.
The grade should be dissolved with pH control during prolonged heating. At pH above 9.0 and temperatures above 80 °C, residual acetate groups can undergo further hydrolysis, shifting the effective alcoholysis degree and changing solution viscosity. Acid-catalysed chain scission may also occur if the solution is held below pH 3.0 at elevated temperature. These boundaries define the safe cooking window for processes that require extended holding before application.
In vinyl acetate and vinyl acetate-ethylene emulsion polymerization, PVA 2688 functions as a steric protective colloid when the aqueous phase is preheated and charged before initiation. Common published recipes use 0.5–5.0 phr on monomer; the high molecular weight raises latex viscosity and improves colloid stability under shear, but also increases reactor torque. In a jacketed reactor with a retreat-blade impeller below 120 rpm, adding PVA 2688 at the upper end of that range can reduce heat transfer because wall-film viscosity increases. High-shear rheology should be measured with a capillary viscometer at 10,000–100,000 s⁻¹ when the latex is formulated for blade coating.
Particle nucleation is influenced by colloid concentration. At high PVA 2688 loadings, homogeneous nucleation can be suppressed and the particle size distribution may broaden, altering the final latex rheology. Published data for the exact particle-size shift in vinyl acetate-ethylene systems using this grade is limited; pilot-scale polymerizations at 1 L and 10 L scale are recommended before production-scale commitment.
Substitution of PVA 2688 for PVA 2488 increases dissolution time and working viscosity; therefore agitation speed and heating time are typically increased. In a dual-blade size press, higher solution viscosity at equal solids can raise blade load and reduce machine speed unless solids are reduced by 1–2 wt%. Replacement of PVA 1799 by PVA 2688 is chosen when lower dissolution temperature and easier clean-up are required, but the dried film will have lower water resistance because residual acetate groups reduce crystallinity and increase swelling.
| Grade | Nominal degree of polymerization | Alcoholysis degree | 4% aqueous viscosity at 20 °C | Key processing difference |
|---|---|---|---|---|
| PVA 2688 | 2600 | 87.0–89.0 mol% | 44.0–52.0 mPa·s | Higher film strength when tested by GB/T 13022-1991; slower dissolution |
| PVA 2488 | 2400 | 87.0–89.0 mol% | 36.0–42.0 mPa·s typical published range | Lower viscosity, easier pumping, moderate film strength |
| PVA 1799 | 1700 typical | ≥99.0 mol% | Not fully soluble at 20 °C; viscosity usually measured at 95 °C | Cold-water-insoluble, higher water resistance after drying |
For paper surface sizing, PVA 2688 is typically run at 6–12 wt% solids in the size press at 50–60 °C. The high molecular weight promotes film continuity and surface strength as evaluated by TAPPI T459 on conditioned handsheets, but the actual pick value is furnish-dependent and is not predicted solely from PVA viscosity. In textile warp sizing, blends with starch at 10–12 wt% total solids are used; PVA 2688 contributes film toughness and abrasion resistance, while the addition rate is limited by sizing-box viscosity and squeeze-roll pickup control.
For water-soluble film and adhesive compounding, PVA 2688 is typically used at 4–8 wt% solids after cooking; the high molecular weight increases open time and film cohesion but also reduces flow and wet-out compared with lower-viscosity grades. Formulations for paper tubes, cores, and carton adhesives may need wetting-agent adjustment because the high solution viscosity can reduce penetration into porous substrates.
Regulatory compliance is formulation-dependent. Polyvinyl alcohol is a polymer under REACH; the supplier safety data sheet is the normative source for registration status. In food-contact adhesive and paper applications, the formulated article must comply with the applicable positive-list requirements such as FDA 21 CFR 175.300, and the resin alone does not confer finished-article compliance.
Incompatibilities include borate ion and certain multivalent metal salts at elevated pH; boric acid at concentrations above a system-specific threshold causes gelation through diol complexation. The grade should not be combined with amine-based additives that shift pH above 9.0 during prolonged heating because ester groups can hydrolyse further and change the effective alcoholysis degree. Storage should avoid temperatures above 40 °C and relative humidity above 60% to prevent lumping and moisture pickup. Prolonged heating above 95 °C under alkaline conditions may shift the hydrolysis distribution and viscosity; therefore cooking should be stopped once the solution clears and no undispersed particles remain.
