Classifications

• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
  • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
  • D06M13/184—Carboxylic acids; Anhydrides, halides or salts thereof
  • D06M13/192—Polycarboxylic acids; Anhydrides, halides or salts thereof

Definitions

• the present invention relates to a method of improving the adhesion properties of polyamide fibers and products derived therefrom, by means of a chemical treatment.
• Polyamide fibers possess numerous favourable properties such as a high elasticity and high tensile strength. In particular, they are suitable for producing fibers because of their high tenacity, rigidity, and wear and abrasion resistance. Fibers of aromatic polyamides excel in particular in having a high modulus, a high strength and a high thermal stability. Therefore, they are pre-eminently suitable for use as a reinforcement in composite materials (composites).
• Takayanagi et al. Polymer J., 19, 467-474 (1987) have described a process for treating the surface of poly-p-phenylene terephthalamide (PPTA)-fiber used as a reinforcement for epoxy resin.
• PPTA poly-p-phenylene terephthalamide
• DMSO dimethylsulfoxide
• the deprotonated (metalated) PPTA is reacted with an alkyl halide or an epoxide resulting into a PPTA fiber having functional groups.
• Reactions of the deprotonated PPTA with other compounds such as acrylonitrile and propylene oxide were also described by Takayanagi et al. (J. Polym. Sci. Polym. Chem.
• the method according to the invention is characterized in that the polyamide fibers or the products derived therefrom are treated with at least one acid halide in an inert, polar, aprotic solvent.
• the acid halide will react with the amide function of the polyamide, substituting a hydrogen atom by an acyl group. This side group may as such or after a further treatment, depending on the nature of the acid halide used, bring about the improved adhesion to matrix materials.
• any acid halide is suitable for the present method.
• the acid halide will be chosen depending on the reactivity of the polyamide, on the desired degree of adhesion improvement and on the nature of the material with which the polyamide fibers are combined.
• an acid halide activated by a second functional group preferably a diacid halide
• a second functional group preferably a diacid halide
• the halide is advantageously a chloride or bromide.
• oxalyl chloride is used.
• the treatment according to the invention is carried out in a solvent which dissolves the acid halide, but which does not react with it to any noticable extent, and which, if necessary, makes the polyamide accessible for chemical reaction. Making the polyamide accessible can be effected by allowing the surface layer of the polyamide fibers to swell somewhat in the solvent; however, the polyamide should not dissolve in the solvent.
• solvents are understood to comprise also mixtures, at least one component of which is polar. Suitable solvents are halogenated hydrocarbons, ethers, ketones, esters, organic nitro compounds, sulfoxides, sulfones, amides and similar solvents. Useful examples of these are chlorobenzene, o-dichlorobenzene, nitromethane, nitrobenzene, tetramethylene sulfone (sulfolane), N-methylpyrrolidone and acetone. In case of aliphatic polyamides, the solvent may be weakly polar or even apolar, like carbon tetrachloride. In case of aromatic polyamides, the solvent should be more polar; preferably sulfolane, optionally combined with another solvent, is used. If desired, the solvent may contain an acid binding agent, but this is not necessary.
• the ratio between acid halide and solvent is not critical and can be, for example, between 2 and 50 vol.% of acid halide in the mixture, but also outside this range if desired.
• the amount of acid halide to be used with respect to the polyamide depends on the desired degree of adhesion improvement, i.e. on the number of amide groups that should be substituted; in general, an excess of acid halide is used.
• the reaction time and the reaction temperature are also chosen according to the desired degree of adhesion improvement.
• the treatment can take a few seconds up to several hours.
• the reaction can be performed at ambient temperature or at elevated temperature, provided that the properties of the polyamide do not decrease.
• the upper limit is usually between 200 and 300°C. If required, the reaction Is performed under pressure.
• the polyamide fibers treated with the acid halide can be used as such for reinforcing the matrix materials, especially if the acid halide has a second functional group which can form bonds with groups present in the matrix material. Such a second functional group can also be used, however, to introduce another, desired, function into the side chain thereby increasing the adhesion properties even further.
• the treated polyamide contains a second acid halide function, it is preferably reacted with a compound containing hydroxy, amino and/or mercapto groups used as a coupling agent, whether or not in an organic solvent.
• This agent may contain other functional groups ensuring a coupling with the matrix material.
• This second functional group can be chosen according to the nature of the matrix material.
• a hydroxy group or epoxy group, or possibly an amino group or thiol group can be selected; for polycarbonates, an amino group is suitable and for other thermoplasts such as poly(vinylchloride), polyolefines, polyacrylates and the like, a vinyl group and a long alkyl group are also suitable; for polyimides, polyamide-imides and polyether-imides, an amino group or a vinyl group is suitable as a bonding improving group; for polysulfones and polyether-sulfones, a thiol group or an amino- or vinyl group combined with a phenylene group is suitable; for poly( ⁇ henylene oxide), a thiol group and for poly(alkylene terephthalates) a methacrylate group, a thiol group or an epoxy group; for elastomers, such as styrene-butadiene rubber, polyurethanes
• the acid halide in the second treatment, can thus be reacted with water, alcohols, carboxylic acids, amines, thiols and such compounds and in particular with bifunctional compounds such as water, diols, hydroxycarboxylic acids, aminoalcohols, diamines, mercaptoalcohols, dithiols, unsaturated alcohols, haloalcohols and epoxyalcohols, whereby the two functions are preferably substituted at the ends of the molecule.
• the bifunctional compounds can also contain a phenylene group or an ester group in their chain.
• Examples are 3-aminopropanol, ethylenediamine, trimethylenediamine, 4-aminobenzyl alcohol, 1,2-ethanedithiol, 1,3-propanedithiol, allyl alcohol, 4-vinylphenol, glycidol, 2-hydroxyethyl methacrylate, 3-chloropropanol etc.
• a possible excess of the acid halide is preferably removed first, in order to avoid possible formation of other polymers.
• water or glycidol is used for epoxy resins and polyesters.
• the polyamide fibers and the products derived therefrom may comprise any kind of polyamide, i.e. both homopolymers and copolymers.
• the polyamides can be derived from aminocarboxylic acids as well as from diamines and dicarboxylic acids.
• the method according to the invention is of particular advantage for fibers of aromatic polyamides, i.e. polyamides containing p- or m-phenylene groups and/or other aromatic groups such as thiazolylene and benzimidazolylene groups in the chain.
• the preferred polyamide Is poly-p-phenyleneterephthtalamide, known under the trade names Kevlar (DuPont) and Twaron (AKZO).
• the process of improving the adhesion properties of polyamide fibers according to the invention may, if desired, be performed continuously.
• the fibers are then passed through a solution of the acid halide and subsequently, if necessary, through a bath containing the coupling compound.
• the fibers Prior to the treatment with acid halide, the fibers can be passed through a bath, optionally heated, containing a solvent only, such as sulfolane, in order to improve the accessibility of the fibers for the acid halide.
• the present invention also relates to the polyamide fibers and products derived therefrom which are thus obtained, having improved adhesion properties.
• the present invention also relates to a method of producing composite materials (composites) wherein polyamide fibers or products derived therefrom having improved adhesion properties are incorporated into a matrix material such as an epoxy resin, a polyester, a polyurethane, a thermoplast, an elastomer and the like, thus transferring the mechanical properties of the polyamide fibers to the composite.
• the present invention therefore also relates to the composites thus produced.
• the process of improving the adhesion of polyamide fibers according to the present invention with respect to matrix materials does not adversely affect the mechanical properties of the polyamide fibers; this is shown by the high tensile strength of the polyamides treated according to the method of the invention which is unchanged with respect to that of the corresponding untreated polyamide fibers.
• SEM scanning electron microscopy
• the nature of the binding with the matrix material ensuring the increased adhesion can vary: full chemical bonding such as by reaction of, for example, an amino or hydroxyl group with an acid chloride group or an epoxy group or of an epoxy group with a carboxylic acid group in the matrix; hydrogen bridging, for example, between a hydroxyl group and an ester or amide group; and lipophllic and similar interactions.
• full chemical bonding provides the greatest improvement in adhesion properties.
• the adhesion or bonding strength can be measured by means of mechanical tests such as pull out tests, providing the maximum force which can be applied on the fiber without the fiber being pulled out of the matrix. This force divided by the embedding depth of the fiber is a measure of the adhesion.
• the bonding strength can also be determined by means of bending tests such as the ILSS (interlaminar shear strength) or on the basis of the fatigue behaviour. In the matrix materials prepared according to the invention, the bonding strength appears to be 20-60% higher than in corresponding materials comprising the polyamide fibers which have not been treated. High temperature curing of the materials (for example 140°C) does not adversely affect the adhesion of the polyamide fibers previously treated according to the invention.
• the method according to the invention can also be used for coupling other groups than adhesion promoting groups to polyamide fibers.
• polyamide fibers and products derived therefrom can be made hydrophobic by reaction of the polyamide treated with acid halide, with a long chain alcohol, optionally in combination with phenyl groups.
• dyes can also be coupled to polyamides, thus providing fibers having a desired colour.
• the method can also be used to make fibers fire resistant by 4544pling the fibers with halogen and/or phosphorous containing groups.
• (meth)acryloyloxyalkyl groups can for example De coupled to the polyamides, whereby the shear strength of the aohesive layer is increased as a result of the cross-linking.
• the epoxy system was that of Ciba-Geigy: epoxy: LY556; curing agent: HT972; cure treatment: (1) from room temperature to 80°C by 2°C/min.; (2) 2 hours at 80°C; (3) from 80°C to 120°C by °C/min.; (4) 2 hours at 120°C; (5) from 120°C to room temperature by 62 ⁇ 3 °C/min.
• Tne bonding strength of the multifilament was determined by means of a bundle pull-out test. Thereby, the end of the fiber is fixed on a hook, which is connected to the force recorder of the tensile strength tester. After the multifilament has been twisted by 1 turn/cm, the epoxy disc is fixed on a specially engineered clamp by applying a slight (pre)strain. The final testing takes place at a rate of 10 mm/min. At the same test configuration and test performance, the pull-out force divided by the embedded length is a measure of the adhesion between fiber/ir.ultifilament and matrix. For a comparison of the bonding strength of the f ibers with different denier/ tex values , it is necess ary to determine the shear strength (N/mm 2 ) defined by
• ILSS values are measured using test rods, made by immersing a fibre bundle in a resin mixture without inclusion of air.
• the number of yarns in the fibre bundle is such that the fibre content of the rods is 50 % by volume.
• the resin is degassed and curing conditions are as described above.
• Example 1 The procedure of Example 1 was followed, with the exception that the fibers treated with sulfolane/oxalyl chloride were not held in water, but instead in methanol. The corresponding results are summarized in Table A.
• Example 3 The procedure of Example 1 was followed, with the exception that the sulfolane/oxalyl chloride treated fibers were not held in water but were first rinsed with dry dichloromethane in order to remove any remaining oxalyl chloride, then held in ethylenediamine, and finally rinsed with dichloromethane again.
• Table A The corresponding results are summarized in Table A.
• Example 1 The procedure of Example 1 was followed, with the exception that the sulfolane/oxalyl chloride treated fibers were not held in water but were first rinsed with dry diethyl ether in order to remove any remaining oxalyl chloride, then immersed in a mixture of glycidol and diethyl ether (1/10 vol/vol) and then again rinsed with diethyl ether.
• Table A The corresponding results are summarized in Table A.
• Example 5 The procedure of Example 4 was followed, with the exception that the fibers were held in the sulfolane/oxalyl chloride bath for only 5 min. (Example 5) and 1 min. (Example 6) respectively, instead of 1 hour.
• Example 1 The procedure of Example 1 was followed, with the exception that the vol/vol-ratio of sulfolane/oxalyl chloride in the bath was 5:1
• Example 7 N/mm (Example 7) and 83 N/mm (Example 8) respectively.
• Example 1 was repeated with the exception that the fibers were held in the sulfolane/oxalyl chloride bath for only 1 min.
• the pull-out force and shear strength values were 78.9 N/mm and 25.3 N/mm 2 respectively.
• Examples 1 and 3 were repeated, with the exception that after the hardening of the epoxy resin, a hot curing treatment at 140°C for 4 hours was performed. The pull-out force was unchanged.
• PPTA-fabric (Kevlar 49-mats from Ten Cate, Type VD 230, extracted) was treated with oxalyl chloride/sulfolane according to the procedure of Example 1 and subsequently, according to Examples 1, 2, 3 and 4, with water, methanol, ethylenediamine and glycidol, respectively.
• the measured carbon, nitrogen and oxygen content of the dry, treated fabrics is summarized in Table C.
• the results of the treated fabrics correspond with those obtained with fibers (compare Table A).

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• Engineering & Computer Science (AREA)
• Textile Engineering (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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• 1988
  • 1988-05-13 NL NL8801252A patent/NL8801252A/nl not_active Application Discontinuation
• 1989
  • 1989-05-10 EP EP19890906196 patent/EP0425504A1/de not_active Withdrawn
  • 1989-05-10 WO PCT/NL1989/000035 patent/WO1989010996A1/en not_active Application Discontinuation
  • 1989-05-10 AU AU36865/89A patent/AU3686589A/en not_active Abandoned

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