PVOH 8548

Polyvinyl alcohol grade PVOH 8548 belongs to the partially hydrolysed, medium-viscosity class of polyvinyl alcohol homopolymers, typically specified for applications requiring a balance between tensile strength development in films and manageable solution viscosity during aqueous compounding. The numerical designation encodes a hydrolysis degree in the range of 86.0–89.0 mol% and a 4 % solution viscosity at 20 °C of 48–56 mPa·s when tested in accordance with JIS K6726. Unlike low-viscosity grades such as PVOH 5-88, which exhibit faster dissolution but inferior film strength, and high-viscosity types such as PVOH 24-88, which demand extended dissolution times and impose higher torque on mixing equipment, PVOH 8548 occupies a processing window that permits rapid solvation in water at temperatures as low as 40 °C while still delivering cohesive film properties suitable for cast and blown extrusion.

Product Specification and Analytical Profile

The base resin is supplied as a free-flowing white to off-white granulate with a bulk density of 0.55–0.70 g/cm³. Particle size distribution is controlled to optimise wetting: retention on a 500 µm sieve does not exceed 5 %, while the fraction passing through 63 µm is maintained below 10 % to minimise dust formation during pneumatic conveying. Volatile matter, determined by weight loss after drying at 105 °C for 3 hours per ISO 15023:2018, is specified at ≤ 5.0 %. Ash content after sulfated ignition per JIS K6726 remains ≤ 0.5 %, a value that translates to negligible deposit formation on sizing reeds, calender rolls and die lips. The pH of a 4 % aqueous solution falls between 5.0 and 7.0, indicating near-neutral residual acetate salt content. Methanol content, a residue from the alcoholysis process, is controlled below 0.5 wt% to reduce volatile organic compound contributions in downstream converting operations. Rheological characterisation of the aqueous solution using a Brookfield LVF viscometer with UL adapter at 20 °C and 60 rpm yields the nominal 48–56 mPa·s range. The viscosity-temperature coefficient follows an Arrhenius relationship, with an apparent activation energy of flow of approximately 22 kJ/mol between 20 °C and 60 °C, allowing predictable thinning under heated coating conditions. The polymer exhibits a glass transition temperature of 58–62 °C by differential scanning calorimetry at 10 K/min, and a melting endotherm peak at 180–190 °C when fully hydrolysed domains re-crystallise during heating. Pre-drying to a residual moisture level of ≤ 0.3 % in a dehumidified hopper dryer at 80 °C for 4–6 hours is mandatory before melt extrusion to prevent bubble defects and hydrolytic chain scission in the barrel.

How Does PVOH 8548 Perform in Cast Film Extrusion for Water-Soluble Packaging?

Cast monolayer film processing on a single-screw extruder with L/D 30:1 and a barrier screw design delivers optimal melt quality when the barrel temperature profile is set from 180 °C at the feed throat to 210 °C at the adapter, with a melt temperature measured at the die entry not exceeding 215 °C. Residence time above 200 °C is limited to less than 2 minutes to prevent acetaldehyde generation and discolouration. A flex-lip die with a gap of 0.5–0.8 mm and a chill roll maintained at 10–15 °C produces film of 25–75 µm thickness. Under these conditions, tensile strength at break, tested per ASTM D882 at 500 mm/min jaw separation, reaches 38–45 MPa in the machine direction and 28–35 MPa in the transverse direction, with elongation at break of 200–300 % and 180–260 % respectively. A critical differentiator is gel particle load. In PVOH 8548, post-polymerisation filtration through sintered metal media with a nominal pore size of 5 µm reduces insoluble gel counts to fewer than 5 gels/m² for particles larger than 150 µm in a 50 µm film, when inspected by automated optical gel counter per ASTM F3597. Competing medium-viscosity grades that omit this filtration step routinely show counts above 20 gels/m², which produce visible fish-eyes and compromised seal integrity in water-soluble unit-dose detergent packs. The film dissolves completely in agitated water at 20 °C within 45 seconds for a 50 µm thickness, measured by the time to clear solution in a dip-dissolution test. Interlayer adhesion during lap-seal formation via thermal or ultrasonic welding is maintained, with seal strengths of 8–12 N/25 mm at a seal temperature of 140–160 °C and dwell time of 0.5 seconds. In air-jet weaving operations where warp yarn abrasion resistance is critical, PVOH 8548 is compounded with polyacrylic acid and lubricating waxes at a solids content of 8–12 %. The size film casts onto cotton or polyester–cotton blends using a single-box slasher at 85–95 °C and squeezed to a wet pick-up of 80–120 %. PVOH 8548 develops a film with a tensile strength exceeding 40 MPa and an elongation at break of 150–200 %, reducing warp breakage rates on high-speed looms operating at 800–1000 picks per minute. Desizing is accomplished with a mild enzymatic or oxidative scour, leaving no persistent residues that would interfere with subsequent dye affinity. The ash content below 0.5 % minimises deposits on yarn guides and reed wires, contributing to a interval between cleaning cycles of over 300 loom-hours in typical operations.

If Rapid Dissolution at 25°C Is Required, PVOH 8548 Outperforms Fully Hydrolyzed Homopolymers

Fully hydrolysed PVOH grades (hydrolysis > 98.0 mol%) require water temperatures above 70 °C for complete dissolution and often form gel agglomerates when added directly to ambient water. PVOH 8548, with a hydrolysis window of 86.0–89.0 mol%, achieves 95 % dissolution within 15 minutes at 25 °C under low-shear agitation (200 rpm in a paddle dissolver) at 4 % solids, as confirmed by turbidity measurements below 5 NTU. The cold-water solubility facilitates preparation of aqueous adhesives for paper converting without the expense of heated make-down vessels. However, care must be taken to add the granules to the vortex of rapidly stirred water to prevent “fish-eye” formation. The solution viscosity remains stable between pH 4.0 and 9.0; outside this range, hydrolysis accelerates, leading to a drift in viscosity during storage. Hard water containing > 300 ppm CaCO₃ equivalent may cause slight cloudiness due to insoluble salt formation with the residual acetate groups, though this does not impair adhesion. The dissolution rate can be further influenced by the particle size distribution mentioned earlier. The controlled fines content prevents the formation of gelled skins on the surface of liquid, a phenomenon common in grades with high sub-63 µm fines. In adhesive formulators using continuous in-line injection systems, PVOH 8548 can be drawn into a Venturi eductor and wetted uniformly, yielding lump-free slurry for downstream dissolution in less than 20 minutes of recirculation.

What Process Boundaries Apply When Crosslinking PVOH 8548 with Glyoxal in D2 Wood Adhesives?

When formulating two-part crosslinking wood adhesives meeting DIN EN 204 durability class D2, PVOH 8548 is typically reacted with glyoxal at a stoichiometric ratio of 0.8:1.0 to 1.2:1.0 based on the accessible 1,2-diol content of the polymer backbone. The crosslinking reaction is acid-catalysed, requiring a pH of 3.5–4.5 maintained by addition of a buffering agent such as citric acid monohydrate at 0.5–1.0 wt% of the liquid adhesive. At 20 °C, the pot life of the catalysed mixture is limited to 6–8 hours, after which the viscosity doubles from an initial 8,000–12,000 mPa·s (Brookfield RVT, spindle 6, 20 rpm) to a non-processable paste. Processing is typically performed on roller coaters with wet-film deposition of 80–120 g/m². Pressing conditions of 0.7–1.0 N/mm² for 2–4 hours at ambient temperature are required to achieve a shear strength exceeding 10 N/mm² on beech substrates. PVOH 8548 provides superior wet tack compared to lower-viscosity grades, reducing assembly time slippage to less than 2 mm at open times of 10 minutes. Incompatibility arises with amine-based co-solvents or additives—including triethanolamine or morpholine—which neutralise the acid catalyst and halt crosslinking progression, leaving unreacted glyoxal that acts as a plasticiser. Furthermore, storage of the glyoxal-crosslinked film above 40 °C triggers retro-aldol cleavage, resulting in embrittlement and loss of water resistance after 72 hours. Therefore, bonded assemblies must be conditioned below 35 °C during initial curing. For formulations requiring longer pot life, alternative dialdehyde crosslinkers with a slower hydrolysis profile may be considered, though they demand an application-specific adhesion validation using EN 302-1 lap-shear specimens.

Viscosity and Hydrolysis Do Not Vary Independently – A Side-by-Side Tabulation

Property	Test Method	PVOH 5-88	PVOH 8548	PVOH 24-88
Hydrolysis degree	JIS K6726	86.0–89.0 mol%	86.0–89.0 mol%	86.0–89.0 mol%
Viscosity (4 % aq., 20 °C)	JIS K6726 / DIN 53015	4.5–6.0 mPa·s	48–56 mPa·s	44–50 mPa·s (note 1)
Volatile matter	ISO 15023	≤ 5.0 %	≤ 5.0 %	≤ 5.0 %
Ash content	JIS K6726	≤ 0.5 %	≤ 0.5 %	≤ 0.5 %
Tensile strength (film)	ASTM D882	20–28 MPa	38–45 MPa	42–52 MPa
Elongation at break	ASTM D882	100–180 %	200–300 %	250–350 %
Dissolution time (95 %, 25 °C, 4 %)	Internal turbidimetric	8–12 min	12–18 min	30–45 min
Gel count (>150 µm, 50 µm film)	ASTM F3597	typically <5 gels/m²	<5 gels/m²	variable, 10–30 gels/m² without filtration

Note 1: High-viscosity designation 24-88 typically exhibits viscosity 44–50 mPa·s for the 4 % solution when the degree of polymerisation is targeted for film-strength parity; conventional 24-88 grades with higher viscosity (e.g., 60–68 mPa·s) also exist but were not included for this direct comparison. All measurements at 20 °C. The juxtaposition reveals that PVOH 8548 delivers 85–90 % of the tensile strength of the high-viscosity analog while requiring only around 40 % of its dissolution time. This positions the grade as a versatile compromise for mixed-process manufacturing environments where both film strength and rapid make-down are required. PVOH 8548 complies with FDA 21 CFR 175.300 for use as a component of resinous and polymeric coatings for paper and paperboard in contact with aqueous and fatty foods, and with FDA 21 CFR 176.170 for components of paper and paperboard in contact with dry food. It is registered under REACH (EC 1907/2006) with a fully up-to-date registration dossier. The substance does not contain candidates for the SVHC Authorisation List above the 0.1 % threshold. The ash value, consistently below 0.5 %, meets the inherent mineral residue requirements referenced in EN 13432 for compostable packaging components, although PVOH itself is biodegradable only in specific activated sludge environments and not in cold marine habitats.