Copolyamide compositions comprising reinforcing fibers and having high modulus stability and uses thereof

A composition configured for injection molding, the composition comprising:

• from 35 to 70% by weight of at least one copolyamide,
• between 35 and 65% by weight of reinforcing fibers;
• from 0 to 10% by weight of at least one impact modifier;
• from 0 to 20% by weight of at least one filler;
• and
• from 1 to 5% by weight of at least one fluidifying agent;
• and
• from 0 to less than 2% by weight of additives,
• with the proviso that the ratio by weight of reinforcing fibers to copolyamide does not exceed 1.75 when the reinforcing fibers are non-circular in cross-section and have a cross-sectional area from 1.5 to 5.0×10−6 cm2;
• the sum of the proportions of each constituent of said composition being equal to 100%;
• and
• the copolyamide comprising at least two distinct units A and X1Y of the formula A/X1Y, wherein:
• A is a repeating unit obtained by polycondensation:
• of at least one C9 to C18 amino acid, or
• of at least one C9 to C18 lactam, or
• of at least one C4-C36 diamine Ca with at least one C4-C36 dicarboxylic acid Cb;
• said at least one diamine Ca being a linear or branched aliphatic diamine, and said at least one Cb diacid being a linear or branched aliphatic diacid, X1Y is a repeating unit obtained from the polycondensation of at least one C9 to C18 linear aliphatic diamine (X1) and at least one aromatic dicarboxylic acid (Y),
• wherein the flexural modulus or tensile modulus of the composition, measured after identical conditioning, does not vary by more than 20% in the temperature range from 20° C. to 40°° C.,
• wherein the fluidifying agent includes an amide prepolymer,
• wherein the amide prepolymer is obtained from a monoamine chain limiter.