Stabilized polyamide
The present invention relates to the use of a polyhydric alcohol in a polyamide polymerization process for giving the modified polyamide obtained increased stability toward heat, light and/or bad weather. The invention also relates to a polyamide modified in this way, and also to polyamide compositions that may be used for the preparation of specific articles liable to be subjected to high temperatures.
1. A process for making a modified polyamide used in articles made for applications exposed to temperatures of greater than or equal to 80° C., comprising:
polymerizing polyamide precursors in a polymerization reactor to form a polyamide; and
adding, before or during the polymerization, a polyhydric alcohol selected from the group consisting of tripentaerythritol, tris(hydroxymethyl)aminomethane and/or a salt thereof, to the precursors and/or polyamide in the polymerization reactor,
wherein, compared to a polyamide made by an analogous process wherein the polyhydric alcohol is added after polymerizing the polyamide precursors, the modified polyamide exhibits improved retention of tensile strength and of impact strength after ageing for 1000 hours at 170° C.; and
wherein a mole proportion of the added polyhydric alcohol that is covalently bonded to the polyamide is between 10% and 100%.
2. The process of claim 1 , characterized in that the hydroxyl groups of the polyhydric alcohol are borne by aliphatic carbons of the polyhydric alcohol.
3. The process of claim 1 , wherein the amount of polyhydric alcohol added before or during the polymerization is from 0.05% to 20% by weight of polyhydric alcohol relative to the total weight of the polyamide and/or precursors thereof.
4. The process of claim 1 , wherein the amount of polyhydric alcohol added before or during the polymerization is from 0.05% to 20% by weight of polyhydric alcohol relative to the total weight of the composition.
5. The process of claim 1 , wherein the polyamide is a semicrystalline polyamide with an apparent melt viscosity of the polyamide of between 0.5 and 1200 Pa·s, measured according to standard ISO 11443 at a shear rate of 1000 s −1 at a temperature equal to 20° C. above the melting point of the polyamide.
6. The process of claim 1 , further comprising: forming the article; and
using the article at temperatures of greater than or equal to 80° C.