PVOH 552 is a fully hydrolyzed polyvinyl alcohol grade supplied as a free-flowing granular or fine powder. The degree of hydrolysis routinely exceeds
98.0 mol%, placing the polymer in the fully hydrolyzed classification according to
JIS K 6726 and
ASTM D 3554 typology. A 4 % aqueous solution prepared under reflux and cooled to
20 °C yields a Brookfield viscosity of
50–60 mPa·s when tested per
ISO 976. Residual acetyl groups are below
0.5 mol%, and the ash content (as Na₂O) is typically held to
≤ 0.5 %. Volatile matter at supply is
≤ 5.0 %, with a bulk density of
0.4–0.6 g cm⁻³. The number-average molecular weight M̄ₙ approximates
85 000–100 000 g mol⁻¹ as estimated by size-exclusion chromatography in aqueous eluent calibrated against narrow poly(ethylene oxide) standards.
Typical physical and chemical specification values for PVOH 552 as supplied.
| Property | Value | Test Method |
|---|
| Degree of hydrolysis | 98.0–99.0 mol% | ISO 15023-1 |
| Viscosity, 4 % solution at 20 °C | 50–60 mPa·s | ISO 976 |
| Ash (as Na₂O) | ≤ 0.5 % | ISO 3451-1 |
| Volatile matter | ≤ 5.0 % | ISO 3251 |
| pH of 4 % solution | 5.5–7.5 | ISO 976 |
| Bulk density | 0.4–0.6 g cm⁻³ | ISO 60 |
What Operational Boundaries Govern High-Solids Adhesive Formulations?
When PVOH 552 is cooked into aqueous adhesives at solids loads above
25 %, the solution viscosity at
60 °C can exceed
15 000 mPa·s. Such pastes are prone to skinning in open vessels; closed-tank cookers with swept-surface agitation are mandatory to maintain homogeneity. The gel-point temperature of a
20 % solution measured by dynamic oscillatory rheometry (
1 Hz,
2 °C min⁻¹ ramp) occurs at
36–39 °C, which confines adhesive transfer temperatures to
≥ 42 °C. Crosslinking with glyoxal or dialdehyde starches—common in bottle-labelling adhesives—shifts the onset of turbidity to higher pH values; formulations buffered to pH
4.5–5.0 with phosphoric acid exhibit pot lives of
8–12 h at
25 °C before viscosity doubling. Beyond
12 h, microgel formation leads to insoluble residue on roll-coater transfer plates, a failure mode repeatedly observed on
500 mm-wide rotary label lines running at
30 000 bottles h⁻¹. Interaction with borax must be avoided; even
0.02 % borax based on PVOH dry weight can elevate the storage modulus at
25 °C by an order of magnitude within minutes due to diol-borate complexation, rendering the adhesive un-pumpable.
In corrugated board lamination, PVOH 552 is co-formulated with
10–15 % plasticizer (glycerol or sorbitol) to suppress film embrittlement at low relative humidity. The equilibrium moisture content of the dried PVOH film at
50 % RH is
5.2 %, whereas at
80 % RH it rises to
12.8 %, causing plasticization and peel-strength fluctuation. Accelerated aging at
40 °C, 75 % RH for
7 days (
ASTM D 3611 ) typically reduces T-peel strength on kraft liner by
18–22 % unless a crosslinker is incorporated. Industrial experience on corrugator belts shows that adhesive pickup weight must stay below
4.5 g m⁻² (dry) to prevent washboarding; a
0.25 mm slotted-die coater operating at
120 m min⁻¹ achieves this with a rheologically stable solution at
28 % solids.
Surface sizing of alkaline fine paper represents a lower-complexity application. A cooked solution of PVOH 552 at
8–12 % solids is applied via a film-size press at
45–55 °C. Pickup of
0.8–1.2 g m⁻² dry polymer raises the surface strength as measured by IGT pick velocity (
ISO 3783) by
0.7–1.0 m s⁻¹ relative to unsized base stock. Because the polymer lacks the particulate nature of a synthetic surface-sizing agent, pore penetration into the sheet is greater, requiring a size-press nip load adjustment to
35–40 N mm⁻¹ to limit internal-sizing interference with AKD or ASA retention.
When PVOH 552 Replaces Partially Hydrolyzed Grades in Water-Soluble Packaging Films
Film producers substituting a partially hydrolyzed grade (hydrolysis
87–89 mol%) with PVOH 552 encounter a pronounced shift in solubility kinetics. Dissolution time of a
50 µm cast film in water at
10 °C increases from
45 s to
210 s; at
40 °C the discrepancy narrows to
12 s versus
18 s. The film requires a minimum water temperature of
35 °C for complete disintegration in under
30 s, limiting its use in cold-water laundry sachets. Tensile properties, however, benefit from the higher crystallinity imparted by near-complete hydrolysis: Young’s modulus at
50 % RH rises from
2.8 GPa to
3.6 GPa, and elongation at break drops from
200 % to
140 %. Blown film extrusion on a single-screw extruder (
L/D = 30, compression ratio
3.5:1) with a die gap of
0.8 mm requires a barrel temperature profile of
185 °C (feed) to
210 °C (die), and melt pressure excursions beyond
180 bar demand the addition of
15 % glycerol to bring the melt flow index under
ISO 1133-1:2022 (
190 °C, 2.16 kg ) into the range of
4–8 g (10 min)⁻¹. Pre-drying of the compound to
≤ 0.3 % moisture is essential at ambient relative humidity above
60 %; failure to pre-dry yields bubble defects and hydrolysis-induced chain scission measurable as a
15–25 % drop in weight-average molecular weight after a single extrusion pass.
A direct comparison with a medium-viscosity partially hydrolyzed grade (designated here as PVOH P) and a lower-viscosity fully hydrolyzed grade (PVOH F) is captured in the following table for blown film processed with
15 % glycerol on identical equipment.
Comparative blown-film properties of PVOH 552 and two reference grades ( 50 µm thickness, conditioned at 50 % RH ).
| Property | PVOH 552 | PVOH P (87 mol% hydro, 45 mPa·s) | PVOH F (98 mol% hydro, 25 mPa·s) | Test Method |
|---|
| Tensile strength (MD) | 78 MPa | 52 MPa | | ISO 527-3 |
| Elongation at break (MD) | 140 % | 220 % | 90 % | ISO 527-3 |
| Water contact angle (static, s) | 61° | 54° | 63° | ASTM D 5946 |
| Disintegration time, 20 °C water | 340 s | 55 s | 240 s | Internal method (stirred beaker) |
| Oxygen transmission rate (OTR) at 23 °C, 0 % RH | 0.5 cm³ m⁻² day⁻¹·atm⁻¹ | 1.2 cm³ m⁻² day⁻¹·atm⁻¹ | 0.4 cm³ m⁻² day⁻¹·atm⁻¹ | ASTM D 3985 |
Regulatory conformity of PVOH 552 aligns with indirect food-contact applications under
FDA 21 CFR 176.170 (components of paper and paperboard in contact with aqueous and fatty foods) when the dried film is not intended for direct ingestion. The grade is registered under
REACH (EC) No 1907/2006 and contains no substance of very high concern (SVHC) listed on the current Candidate List. Heavy-metal content falls below the limits prescribed by
EN 71-3 (migration of certain elements) and the material satisfies the substance restrictions of
EU Directive 2011/65/EU (RoHS). Published toxicological profiles show an acute oral LD₅₀>
5 000 mg kg⁻¹ (rat), confirming classification as non-hazardous. Combustion releases primarily carbon dioxide and water; thermal decomposition in air begins at approximately
230 °C, as determined by thermogravimetric analysis (
10 °C min⁻¹, nitrogen atmosphere). Any off-gas containing acetic acid at elevated processing temperatures must be vented, but under standard thermoplastic processing windows (
≤ 210 °C), release remains below the odor threshold that would breach industrial hygiene monitoring per
ISO 16000‑6.
Controlling Gelation During Hot-Melt Adhesive Compounding
When PVOH 552 is plasticized with glycerol and extruded into reactive hot-melt rods, gel particle generation becomes the dominant quality defect. In a co-rotating twin-screw extruder (
L/D = 40, screw diameter
27 mm ) with a temperature profile of
110 °C (zone 1) to
195 °C (die), the low free volume of the fully hydrolyzed polymer limits plasticizer diffusion. A split feeding of glycerol—
60 % at the feed throat and
40 % injected at barrel zone 6 via a gear pump—reduces the residual crystalline fraction detected by modulated DSC from
18 % to
4 %. Screw configurations employing kneading blocks with
90° staggering over two elements followed by a reverse-flight element generate localized specific mechanical energy inputs of
0.25–0.30 kWh kg⁻¹, which suffices to disrupt crystallite lamellae without triggering chain degradation. Any hold-up in the die adapter at temperature above
205 °C for more than
3 min promotes cross-esterification with residual acetate groups, forming micro-gels visible as fish-eyes in
0.5 mm cast films. This failure mode has been documented on commercial compounding lines where downstream pelletizing-water temperature fluctuated above
30 °C, causing pellet agglomeration and requiring offline screening through a
500 µm sieve. Optimal pellet quality, defined as a yield of particles between
250 µm and
800 µm exceeding
92 %, is achieved with an underwater pelletizer inlet water temperature held at
12–15 °C and a die-plate temperature of
195 °C.
