Nylon Blends with Reduced Moisture Absorbance

Polyamides, such as nylon 6 and nylon 6,6 and mixtures thereof, show good affinity for polyester resins bearing sulfonate salt functionality. Sulfonate salt functional groups, even when present at low levels (0.5 mole %) help to compatibilize the sulfonate salt resin with nylon. Such blends have a very fine morphology and also show reduced moisture content compared to the base nylon.

The extent of moisture reduction will depend of the amount of polyester in the blend Higher levels of polyester will give less moisture uptake. The Table 1 shows the reduce moisture uptake immersed in water at room temperature for a 1:1 blend of nylon 6,6 with a PBT resin with 1 mole % sodium sulfo isophthalate functionality (SPBT). Blends of polyamides made be made with, for example 1-90 wt% sulfonate polyesters, blends of from 10-50 wt% maybe be preferred in some cases where the polyamide is desired as the continuous phase.

Weight Gain %
Days 50 % RH	1:1, 1%SPBT:PA6,6	PA 6,6
0	0	0
1d	0.85	1.5
2d	1.25	3.1
6d	1.9	4
8d	2.3	5.7
14d	2.9	7.3

This blend technology can give shaped article, especially fibers, with reduced moisture absorption and less change in properties with moisture content compared to unblended polyamides.

Sulfonate salt modified polyesters, sometimes called polyester ionomers and their bends with polyamides are described in many references, for instance US 6,495,079 and references therein.

DESCRIPTION OF SULFONATE POLYESTERS

The term polyester ionomer, or sulfonate polyester or metal sulfonate polyester, refers to polyester polymers derived from the reaction residue of an aryl carboxylic sulfonate salt, an aromatic dicarboxylic acid, an aliphatic diol or any of their ester forming derivatives. The ionomer polyester polymers comprise some monovalent and/or divalent sulfonate salt units represented by the formula IA:

or formula IB:

(M⁺ⁿ O₃S)_d-A-(OR”OH)_p

wherein p=1-3; d=1-3, and p+d=2-6, and A is an aryl group containing one or more aromatic rings: for example, benzene, naphthalene, anthracene, biphenyl, terphenyl, oxy diphenyl, sulfonyl diphenyl or alkyl diphenyl, where the sulfonate substituent is directly attached to an aryl ring. These groups are incorporated into the polyester through carboxylic ester linkages. The aryl groups may contain one or more sulfonate substituents; d = 1-3 and may have one or more carboxylic acid linkages; p = 1-3. Groups with one sulfonate substituent (d =1) and two carboxylic linkages (p = 2) are preferred. M is a metal, n = 1-5. Preferred metals are alkaline or alkaline earth metals where

n = 1-2. Zinc and tin are also preferred metals. R” is an alkyl group: for example,

-CH₂CH₂-, -CH₂CH₂OCH₂CH₂-, -CH(CH₃)CH₂-, CH₂CH₂CH₂-, -CH₂CH₂CH₂CH₂-

Typic...