Method of Preparing Crosslinked Poly(vinyl Alcohol)

Crosslinked poly(vinyl alcohol) is a known water-loss agent in oil well drilling fluids.

The instant invention is directed to a novel process for preparing the crosslinked poly(vinyl alcohol) product.

In the processes of the prior art, crosslinked poly(vinyl alcohol) is made in two steps. In the first step, poly(vinyl acetate) is hydrolyzed and recovered. In the second step, the hydrolyzed product is treated with an aldehyde to crosslink it. The process of this invention combines both steps, thereby saving time, money, reactants and apparatus.

The following (simulated) examples demonstrate the inventive process.

One hundred grams of a poly(vinyl acetate) latex, containing 55% poly(vinyl acetate) by weight is acidified to pH 1.0 with HCl. 1.3 g of 37% formaldehyde is added and the mixture is heated to 80.degree. C. for 5 hours with stirring. The product is then recovered by salting out with Na.sub.2 SO.sub.4 and filtration, and dried at 70.degree. C. The dried product is ground to pass through a 16 mesh screen.

The product is tested for performance by adding 1.5% of the product by weight and mixing with a 6% sodium bentonite slurry. The API fluid loss is 7 ml compared to 14 ml for the bentonite without fluid loss controller.

The reaction described in Example 1 is carried out in a 16% Na.sub.2 SO.sub.4 aqueous solution. This results in the swelling of the polyvinyl alcohol instead of the dissolution. After the crosslinking reaction is completed, the product can be recovered by filtration.

In this variation, any liquid which results in a swollen polyvinyl alcohol can be used, but 16% Na.sub.2 SO.sub.4 is preferred. The Na.sub.2 SO.sub.4 concentration can vary by 2-3%, but 16% is close to saturation at ambient temperature.

The latex concentration can vary. It can be as high as 60%, or as low as desired, e.g., 5-60%. The pH can be anywhere on the acid side, the lower the pH, the quicker the reaction. pH 1.0-1.5 is preferred, but 0-4 can be used. The subject ratio of poly(vinyl acetate) solids:aldehyde solids can be about 50-200:1.

Slightly higher or lower levels of formaldehyde can be used, depending on the degree of crosslinking desired. Other aldehydes can also be used, especially the dialdehydes, glyoxal and glutaraldehyde. With the dialdehydes 0.1-0.05 g/100 g of 55% latex is preferred for effective crosslinking. Other suitable aldehydes include, for example, acetaldehyde, propionaldehyde, glycolaldehyde, glyoxylic acid and the like or polyaldehydes, i.e., organic compounds having more than one aldehyde group in the compound, such as glyoxal (already mentioned), paraformaldehyde and the like. Other suitable aldehyde reactants include aldehyde generating agents, i.e., known organic compounds capable of forming an aldehyde group in situ, such as melamine-formaldehyde monomeric products and derivatives such as tri and hexa(methylol) melamine. Such materials can be formed by known conventional methods. The alkyl blocked derivatives are commercially available, are stable to self polymerization and are, therefore, preferred. Of all of the aldehyde reactants, the preferred reactants are paraformaldehyde, formaldehyde, glyoxal, and glutaraldehyde.

The reaction temperature can be varied between ambient (e.g., 20.degree. C.) and 100.degree. C., with 60.degree.-80.degree. C. being preferred. Reaction time can vary between 30 minutes and 24 hours.

Any standard method of separating the final product from the liquid phase can be used, including filtration, decantation, or evaporation. Drying temperatures can vary between 50.degree. and 100.degree. C., with 70.degree.-80.degree. C. being preferred. Any preferred mesh size can be used for the final product.