Abstract:
A process for recycling polyoxymethylene polymers is disclosed. A polyoyxmethylene polymer is at least partially dissolved in an aprotic compound. The resulting solution or suspension (liquid mixture) is then contacted with a catalyst which causes the polyoxymethylene polymer to be converted into a cyclic acetal. The cyclic acetal can be separated, collected and used in other processes. In one embodiment, the cyclic acetal may be used to produce a polyoxymethylene polymer.
Abstract:
A process for producing cyclic acetals is described. A formaldehyde source is contacted with an aprotic compound in the presence of a catalyst to produce the cyclic acetals. The aprotic compound can increase conversion rates and/or efficiency. In one embodiment, the formaldehyde source is obtained from methanol. In particular, methanol can be converted into formaldehyde which is then converted into a cyclic acetal. In one embodiment, the cyclic acetal can then be used to produce oxymethylene polymers.
Abstract:
Process for manufacturing oxymethylene copolymers stabilized against thermal degradation, comprising the heating of the copolymer in a medium containing water and a disubstituted cellulose ether.
Abstract:
The alkali metal, ammonium and alkanol ammonium salts of polymeric acetal carboxylates are stable detergent builders under laundry use conditions but depolymerize at lower pH, making the polymer fragments more readily biodegradable in waste streams. Such polymeric acetal carboxylates can now be made by an improved process which includes the steps of bringing together in a reaction zone under polymerization conditions an ester of glyoxylic acid and a polymerization initiator, and adding an alkyl vinyl ether to the resulting polymer in the presence of a solvent having a dielectric constant of at least 15, such as an alkyl nitrile and a haloacetic acid catalyst, such as trifluoroacetic acid, to stabilize the polymer against rapid depolymerization in alkaline solution. The preferred solvent is acetonitrile.
Abstract:
Oxymethylene copolymer having heat and hydrolysis resistant terminal groups is prepared by heating the polymers present in a liquid phase, whereby a thermal degradation of the unstable terminal groups takes place. The degradation is advantageously effected in the presence of a calcium or magnesium salt of an aliphatic carboxylic acid of low molecular weight. The oxymethylene copolymers are suitable as engineering plastic for preparing semi-finished products and finished products.
Abstract:
A PROCESS FOR IMPROVING THE THERMAL STABILITY OF COPOLYMERS OF TRIOXANE WHICH CONTAIN AT LEAST 80% BY WEIGHT OF -O-CH2- GROUPS AND ISTRIBUTED IN THE POLYMER CHAIN IN AMOUNTS OF LESS THAN 20% BY WEIGHT (WITH REFERENCE TO THE COPOLYMER) OF (-)3C-C(-)3 GROUPINGS BY ELIMINATING UNSTABLE PORTIONS OF THE CHAIN BY HEATING WITH AQUEOUS SOLUTIONS OF ALKALI METAL OR ALKALINE EARTH METAL FLUORIDES.
Abstract:
A process for recycling polyoxymethylene polymers is disclosed. A polyoxymethylene polymer is at least partially dissolved in an aprotic compound. The resulting solution or suspension (liquid mixture) is then contacted with a catalyst which causes the polyoxymethylene polymer to be converted into a cyclic acetal. The cyclic acetal can be separated, collected and used in other processes. In one embodiment, the cyclic acetal may be used to produce a polyoxymethylene polymer.
Abstract:
A process for recovering volatile components from an oxymethylene polymer process is disclosed. The volatile components are removed from the process and the formaldehyde collected is converted to a cyclic acetal. The formaldehyde is converted to a cyclic acetal by contacting the formaldehyde with a catalyst in the presence of an aprotic solvent.
Abstract:
An improved method of stabilizing a polyoxymethylene copolymer, which comprises(1) heat-melting a crude copolymer of trioxane and a cyclic ether and/or a cyclic acetal to form a first stabilized copolymer having a decomposition ratio (D.sub.220.sup.60), determined when it is heated at 220.degree. C. for 60 minutes in vacuum, of up to 2% by weight, and then(2) bringing the first stabilized copolymer into contact with steam containing 0.01 to 5% by weight of a basic compound at a temperature of at least 100.degree. C. but not exceeding the melting point of the copolymer to form a second stabilized copolymer.
Abstract:
Oxymethylene copolymers molding compositions with low portions of residual formaldehyde are produced by heating the polymerizate melts treated with chemical stabilizers in an apparatus in which there are continuously presented new polymerizate surfaces under reduced pressure. The heating of the polymerizate melt takes place in a thin layer evaporator for highly viscous media during an average residence time of 30 to 120 seconds at an average rate of shear between 500 and 2000 s.sup.-1 and at a pressure P.sub.abs of at most 150 mbar. The escaping gases and vapors are drawn off countercurrent to the polymerizate melt.