Composite polyamide article
Uses of low molecular mass, non-evolutive polyamide resins for making composite articles are described. Articles obtained from such resins having good mechanical properties, such as rigidity, breaking load, impact resistance, and fatigue behavior in particular, even when the articles are manufactured according to cycles shorter than those usually used, and without any processing before or after the manufacture of the composite articles, are also described.
1. A process for the manufacture of a composite article by molding, the process comprising at least the following steps:
a) obtaining a composition comprising a non-evolutive polyamide resin having a weight-average molecular weight Mw of between 5000 g/mol and 25000 g/mol and a concentration of amine terminal groups (ATG) of less than or equal to 5 meq/kg and a concentration of carboxylic terminal groups (CTG) of between 100 and 1000 meq/kg, or a concentration of carboxylic terminal groups (CTG) of less than or equal to 5 meq/kg and a concentration of amine terminal groups (ATG) of between 100 and 1000 meq/kg,
b) impregnating at least one reinforcing cloth with the composition comprising the non-evolutive polyamide resin in a molten state; and
c) cooling and then recovering the composite article,
wherein the polyamide has been subjected to a finishing step under vacuum, and
wherein the molecular weight of the non-evolutive polyamide resin does not change during the manufacture of the composite article.
2. The process as claimed in claim 1 , wherein the polyamide is selected from the group consisting of polyamides obtained by polycondensation of at least one linear aliphatic dicarboxylic acid with an aliphatic or cyclic diamine, or between at least one aromatic dicarboxylic acid and an aliphatic or aromatic diamine, polyamides obtained by polycondensation of at least one amino acid or lactam with itself, blends thereof, and (co)polyamides thereof.
3. The process as claimed in claim 1 , wherein the polyamide resin has a weight-average molecular weight Mw of between 10000 g/mol and 15000 g/mol.
4. The process as claimed in claim 1 , wherein the impregnation of the reinforcing cloth with the polyamide composition is carried out by bringing the polyamide composition in the molten state into contact with the reinforcing cloth.
5. The process as claimed in claim 1 , wherein the impregnation of the reinforcing cloth with the polyamide composition is carried out by bringing the reinforcing cloth into contact with the polyamide composition in the form of a powder or of a film and then melting said polyamide composition.
6. The process as claimed in claim 1 , wherein the article comprises between 25% and 70% by volume of reinforcing cloth, relative to the total volume of the article.
7. The process as claimed in claim 1 , wherein the reinforcing cloth comprises reinforcing yarns and/or fibers selected from the group consisting of yarns and/or fibers of carbon, glass, aramids, polyimides, flax, hemp, sisal, coir, jute, kenaf and mixtures thereof.
8. The process according to claim 1 , wherein the polyamide is selected from the group consisting of PA 6.6, PA 6.10, PA 6.12, PA 12.12, PA 4.6 and MXD 6.
9. The process according to claim 8 , wherein the polyamide is PA 6.6.
10. The process according to claim 1 , wherein the concentration of amine terminal groups (ATG) is less than or equal to 5 meq/kg and the concentration of carboxylic terminal groups (CTG) is between 100 and 1000 meq/kg.
11. The process according to claim 10 , wherein the concentration of amine terminal groups (ATG) is 0 meq/kg.