Celvol polyvinyl alcohols have many characteristics which make them useful in a wide range of applications. By choosing among the many Celvol polyvinyl alcohol grades available, it is possible to obtain the performance properties required for your specific applications-properties such as water solubility, abrasion resistance, tensile strength, adhesive and bonding properties, grease or oil resistance and film forming qualities. Our highly skilled technical service group can help you with Celvol polyvinyl alcohol grade selection.

Changes Occurring in the Properties of Polyvinyl Alcohol
as the Degree of Hydrolysis and Molecular Weight Change


Physical Properties
Celvol polyvinyl alcohol combines high tensile strength with ease of film formation. Additionally, Celvol resins show excellent adhesive and bonding characteristics. Partially hydrolyzed grades have better adhesion to hydrophobic surfaces.

The degree of hydrolysis affects the water sensitivity of both the resin and film. Water resistance increases with increasing hydrolysis. The super hydrolyzed grades should be used when maximum water resistance and humidity resistance are desired.

Celvol polyvinyl alcohol resins are generally unaffected by greases, petroleum hydrocarbons and animal or vegetable oils. Resistance to organic solvents increases with the degree of hydrolysis. Celvol polyvinyl alcohol film can be plasticized with glycerol or the lower molecular weight glycols. These materials generally act as humectants, holding water in the film.

Physical Properties of Polyvinyl Alcohol

Appearance	White-to-cream granular powder
Bulk Density	40 lbs/cu ft
Specific Gravity
— of solid	1.27 - 1.31
— of 10 wt % solid at 25°C	1.02
Thermal Stability	Gradual discoloration about 100°C; darkens rapidly above 150°C; rapid decomposition above 200°C
Thermal Conductivity, W/(m•K)3	0.2
Electrical Resistivity, ohm•cm	(3.1 - 3.8) x 107
Specific Heat,
J/(g•K)b	1.5
Melting Point
(unplasticized), °C	230 for fully hydrolyzed grades; 180-190 for partially hydrolyzed grades
Tg, °C (dry film)	75-85
Storage Stability (solid)	Indefinite when protected from moisture
Flammability	Burns similarly to paper
Stability to Sunlight	Excellent

Notes
a.  To convert W/(m•K) to (Btu•in)/(h•ft2•F), divide by 0.1441.
b.  To convert J to cal, divide by 4.184.

Chemical Reactions
Polyvinyl alcohol resins react in a manner similar to other secondary polyhydric alcohols. Esterification reactions of polyvinyl alcohol can be carried out with a number of compounds. A commercially important reaction is the formation of tackified PVOH using boric acid or borax to form cyclicesters. This reaction is very sensitive to pH, and an insoluble gel is formed above 4.5-5.0.

Other esterification reactions include those with chloroformate esters to yield polyvinyl carbonate, with urea to yield a polymeric carbamate ester, and with isocyanates to form substituted carbamate esters.

Another commercially important reaction is acetalization with aldehydes. Polyvinyl butyral is produced by the reaction of polyvinyl alcohol with butyraldehyde and is used in the production of the inner adhesive film for safety glass. Reaction with dialdehydes such as glyoxal or gluteraldehyde can be used to crosslink polyvinyl alcohol. Other reactions include ethoxylation, propoxylation and cyanoethylation.

Crosslinking
All polyvinyl alcohol grades are crosslinkable through their secondary hydroxyl functionality. Even lower hydrolysis grades—which are so exceptional on paper surfaces for oil, grease and organic solvent resistance and Gurley porosity—can be made water resistant. Degrees of water resistance vary from grade to grade. The table below shows the effect of glyoxal, a commonly used and favored crosslinker for polyvinyl alcohol. When glyoxal was added to Celvol grades 540, 350 and 165 polyvinyl alcohol at 20% dry-on-dry, significant water resistance improvements resulted. Note that the wet tensile of Celvol 540 polyvinyl alcohol increased from no measurable wet strength uncrosslinked to 6.1 pli when crosslinked. Also, the wet tensile of crosslinked Celvol 350 polyvinyl alcohol was more than double that of uncrosslinked Celvol 350, and crosslinked Celvol 165 polyvinyl alcohol was 28% higher than uncrosslinked Celvol 165.

A vast array of crosslinkers or insolubilizers are available. They include several classes: (1) aldehydes, of which glyoxal, a simple dialdehyde, is the most common, along with higher aldehydes, such as gluteraldehyde and hydroxyadipaldehyde; (2) thermosetting resins, such as urea-formaldehyde and melamineformaldehyde; and (3) salts of multivalent anions, such as zirconium ammonium carbonates.

More recently, there has emerged a growing interest in zero-formaldehyde, or low-formaldehyde-type crosslinkers. Two such products are Polycup 172, a water soluble, polyamide-epichlorohydrin-type resin, and Bacote-20, a zirconium ammonium carbonate salt. The results in the table below indicate that the addition of Polycup 172 to Celvol 165 polyvinyl alcohol at 5% dry/dry parts was as effective as glyoxal added at 20%, both resulting in a 26% wet tensile improvement. The addition of 5% Bacote-20 resulted in an 11% wet tensile improvement.

Effect of Glyoxal on Polyvinyl Alcohol Wet Tensile Strength Chromatography Base Paper*

Celvol Grade	% Hydrolysis Spec. Range	% Glyoxal Dry/Dry	Wet Tensiles, pli (3 Min in 1% Aerosol OT Solution)
540	87-89	None	0.0
540	87-89	20	6.1
350	98-98.8	None	3.2
350	98.98.8	20	6.6
165	99.3+	None	6.7
165	99.3+	20	8.6

Note:
* 9 add-on level based on fiber; cure 5 min @ 149°C.

Effect of Crosslinker Type on Wet Tensile of Celvol 165 Polyvinyl Alcohol-Saturated Paper*

Crosslinker	% Dry/Dry	Instron Wet Tensile (CMD) pli
None	—	6.4
Glyoxal	20	8.0
Bacote-20	5	7.1
polycup 172	5	8.1

Note:
*  Whatman No. 4 chromatography paper
10% Celvol 65 add-on
Drying Conditions were 5 min @ 149°C.