Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/20—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the epoxy compounds used
  • C08G59/32—Epoxy compounds containing three or more epoxy groups
  • C08G59/3218—Carbocyclic compounds
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
  • C03C25/10—Coating
  • C03C25/24—Coatings containing organic materials
  • C03C25/26—Macromolecular compounds or prepolymers
  • C03C25/32—Macromolecular compounds or prepolymers obtained otherwise than by reactions involving only carbon-to-carbon unsaturated bonds
  • C03C25/36—Epoxy resins
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
  • C03C25/10—Coating
  • C03C25/24—Coatings containing organic materials
  • C03C25/26—Macromolecular compounds or prepolymers
  • C03C25/28—Macromolecular compounds or prepolymers obtained by reactions involving only carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C25/00—Surface treatment of fibres or filaments made from glass, minerals or slags
  • C03C25/10—Coating
  • C03C25/24—Coatings containing organic materials
  • C03C25/40—Organo-silicon compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/40—Glass
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K9/00—Use of pretreated ingredients
  • C08K9/04—Ingredients treated with organic substances
  • C08K9/06—Ingredients treated with organic substances with silicon-containing compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
  • C08L33/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
  • C08L33/04—Homopolymers or copolymers of esters
  • C08L33/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, which oxygen atoms are present only as part of the carboxyl radical
  • C08L33/062—Copolymers with monomers not covered by C08L33/06
  • C08L33/064—Copolymers with monomers not covered by C08L33/06 containing anhydride, COOH or COOM groups, with M being metal or onium-cation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L67/00—Compositions of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Compositions of derivatives of such polymers
  • C08L67/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
  • C09D133/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
  • C09J133/062—Copolymers with monomers not covered by C09J133/06
  • C09J133/064—Copolymers with monomers not covered by C09J133/06 containing anhydride, COOH or COOM groups, with M being metal or onium-cation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/40—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the curing agents used
  • C08G59/42—Polycarboxylic acids; Anhydrides, halides or low molecular weight esters thereof
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2363/00—Characterised by the use of epoxy resins; Derivatives of epoxy resins
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
  • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
  • C08J5/06—Reinforcing macromolecular compounds with loose or coherent fibrous material using pretreated fibrous materials
  • C08J5/08—Reinforcing macromolecular compounds with loose or coherent fibrous material using pretreated fibrous materials glass fibres
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2203/00—Applications
  • C08L2203/12—Applications used for fibers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/03—Polymer mixtures characterised by other features containing three or more polymers in a blend
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L63/00—Compositions of epoxy resins; Compositions of derivatives of epoxy resins
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
  • Y10T428/2913—Rod, strand, filament or fiber
  • Y10T428/2933—Coated or with bond, impregnation or core
  • Y10T428/2962—Silane, silicone or siloxane in coating

Definitions

• the present invention relates to the field of g lass fibre reinforced composites and, in particular, of silane based sizings for glass fibres en hancing the mechan ical properties of polymeric composites reinforced with glass fi bres coated with such sizing measu red both dry as moulded (DAM) and after ageing in moist conditions.
• the sizing composition of the present invention is suitable for coating glass fibres for reinforcing various types of polymeric matrices, most particularly thermoplastic polyesters such as PET. Background for the invention
• Fibre reinforced composites wherein approximately 6 to 25 ⁇ diameter fibres having high stiffness and /or strength, typically carbon, glass or aramide fibres, are embedded in a polymeric matrix have substantially h igher mechan ical properties allowing to reach very advantageous mechanical properties to density ratios.
• the reinforcing fibres may be short, long or continuous.
• the mechanical properties of continuous fibre reinforced composites can be very high, the geometry of parts made of such composites is limited mostly to thin wall geometries.
• the mechanical properties of short fibre reinforced composites are lower than the former, there is no li mit to the geometry of part man ufactured therewith, as they can be produced by extrusion or injection moulding.
• the fibres are coated with a sizing which com position depends on the nature of the reinforcing fibre to be sized and on the matrix the fibres are to be used with.
• Glass fibres are usually sized with a silane based composition since Si-O-Si covalent bonds can be formed between, on the one hand, the g lass fibre surface and silanols obtained by hydrolysing of the alkoxysilanes of the sizing and, on the other hand , between adjacent silanol grou ps, thus forming a crossl inked structure at the surface of the glass fibres.
• This crosslinked structure seems to enhance the fibre resistance to corrosion, typically to hydrolysis.
• Adhesion of the sizing with the matrix can be enhanced by the organic function of the silane coupling agent and by a fil m former, which nature depends on the matrix used.
• Sizing compositions usually comprise other add itive such as a lubricant, antistatic agents, and the like.
• Sizing compositions can be applied to the fibre surface at a single coating station or, can be formulated as a two-part composition to be applied at two coating stations.
• the latter techn ique permits to formulate sizing compositions combining components which are reactive with one another, which would be unsuitable for a one-station application process because of their limited shelf life.
• Two part sizing compositions are usually composed of a precursor applied first to the surface of the fibres, and of a binder applied thereafter. They are most suited for chopped fibres, wherein the precursor is applied to the fibre surface as they are drawn out of a bushing. The precursor coated fibres are then chopped and collected into a container wherein they are coated with the binder, usually by spraying thus forming fibre pellets.
• a thermal treatment is then applied to the fibre pellets to evaporate water and to react the components of the sizing composition with the glass fibre surface and with one another.
• the sized fibre pellets can advantageously be blended with a thermoplastic polymer in the screw of an extruder, wherein the fibre pellets are disrupted and the length of the fibres further decreased while they are homogenously mixed with the polymer;
• An extruded profile generally in the shape of a wire, is chopped to form composite pellets of the polymer loaded with short glass fibres. Said composite pellets can be melted and shaped into a final part by injection moulding or extrusion.
• the present invention proposes sizing compositions for glass fibres which yield high mechanical properties measured both dry as moulded (DAM) and after ageing in moist conditions.
• DAM dry as moulded
• the sizing is particularly effective with thermoplastic polyester matrices.
• the present invention is defined in the appended independent claims. Preferred embodiments are defined in the dependent claims.
• the present invention concerns a two-part sizing composition comprising:
• a binder comprising a multifunctional epoxy resin of functionality, F > 3
• the anhydride contained in said polymer or copolymer is maleic anhydride
• the carboxilic acid contained is said polymer is polyacrylic acid.
• the total amount of polymer or copolymer containing carboxylic acid and/or anhydride of functionality, F > 3 is preferably present in the dry composition in an amount comprised between 5.0 and 60.0 wt.%, more preferably between 1 5.0 and 30.0 wt.%
• said multifunctional epoxy resin may comprise a novolac type epoxy, preferably epoxy phenol novolac (EPN) or epoxy cresol novolac.
• Said multifunctional epoxy resin is preferably present in the dry composition in an amount comprised between 30 and 90 wt.%, more preferably between 50 and 70 wt.%.
• the aminosilane is preferably selected from one or more of an;
• aminodialkoxysilane such as ⁇ -aminopropylmethyldiethoxysilane, N- -(Aminoethyl)-gam ma-am inopropylmethyldimethoxysi lane, ⁇ - ⁇ - (Aminoethyl)-y-aminopropyl-methyldimethoxysilane, N- -(Aminoethyl)- y- aminoisobutylmethyldimethoxy-silane, y-am inopropylmethyldimethoxysi lane, N- -(Aminoethyl)- y -aminopropyl-methyldiethoxysilane, and/or
• aminotrialkoxysilane such as y-aminopropyltriethoxysilane, y- aminopropyltrimethoxysilane, N- ⁇ -(Aminoethyl)- y-aminopropyl-tri- methoxysilane, N- -(Aminoethyl)- y-aminopropyltriethoxysilane, diethylene- triaminopropyltrimethoxysilane, Bis-(y-trimethoxysilylpropyl) amine, N- phenyl- y-am inopropyltrimethoxysi lane, y-amino-3,3-dimethylbutyltri- methoxysilane, y -aminobutyltriethoxysilane, polyazamide silane.
• aminotrialkoxysilane such as y-aminopropyltriethoxysilane, y- aminoprop
• Said aminosilane is preferably present in the dry composition in an amount comprised between 2.5 and 20.0 wt.%, more preferably between 5.0 and 1 5.0 wt.%.
• the sizing of the present invention may also comprise a film former.
• Film formers preferably comprise a polyurethane or a (meth-)acrylate polymer or co-polymer, or mixtires thereof, said film former being preferably present in the precursor in a n amount of 0.1 to 50.0 wt.% with respect to the total dry weight of the composition, more preferably 1 0.0 to 30.0 wt. %;. It may further comprise additives selected from on e or more of:
• pH adjusters such as bases, preferably ammonia or sodium hydroxide, and acids, preferably acetic acid or phosphoric acid
• a non-ionic lubricant preferably a fatty alcohols ethoxylated or fatty acid monoester of polyethylene glycol, such as PEG 200 Monolaurate, PEG 600 Monooleate, PEG 600 Monostearate, PEG 400 Monostearate PEG 400 Monooleate, PEG 600 Monolaurate
• the non-ionic lubricant being preferably present in an amount of 0.1 to 30.0 wt.% solids, more preferably from 1 .0 to 20.0 wt.% solids, most preferably from 2.0 to
• a cationic lubricant such as a polyethyleneimine polyamide salt
• a cationic lubricant is preferably present in the size composition in an amount from 0.1 to 30.0 wt.% solids, more preferably from 1 .0 to 20.0 wt.% solids, most preferably from 2.0 to 5.0 wt.% solids,
• an antistatic agent such as a quaternary ammonium, a tetraethylammonium chloride, or lithium chloride, and is preferably present in an amount of 0.1 to 5.0 wt.% solids, preferably from 0.5 to 1 .5 wt.% solids.
• anti-foaming agents such as polysiloxane derivatives, the anti-foaming agent being preferably present in amount of less than 0.1 % of total weight of sizing without water, ⁇ an isocyanate based cross-linker, such as an isocyanurate, biuret, carbodiimide, the isocyanate based cross-linker being preferably present in amount of 0.1 to 50% of total weight of sizing without water, more preferably between 1 0 and 30.0 wt.%;
• a boron-containing compound selected from the group consisting of boric acid, boron oxide, sodium tetraborate, potassium metaborate, potassium tetraborate, ammonium biborate, ammonium tetrafluoroborate, butylammonium tetrafluoroborate, calcium tetrafluoroborate, lithium fluoroborate, potassium tetrafluoroborate, sodium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate and zinc tetrafluoroborate;
• the boron containing compound is preferably present in an amount of 0.1 to 50.0% with respect to the total dry weight of the composition, more preferably between 1 0.0 to
• the present invention further concerns a glass fibre at least partially coated with the reaction product of a sizing composition as discussed above.
• the two-part sizing of the present invention may be applied to the surface of glass fibres with the following steps: (a) Forming glass fibres out of a bushing,
• the glass fibres are chopped into short fibres after the application of the precursor, which is preferably applied with a roller, and before the application of the binder, which is preferably applied by spraying.
• Glass fibres according to the present invention are advantageously used in a fibre reinforced composite comprising a polymeric matrix, which preferably comprises a thermoplastic polymer such as a polyester, more preferably PBT or PET, and most preferably PET.
• a polymeric matrix in a fibre reinforced composite material is meant herein as the binding phase of a fibre reinforced composite. It comprises a polymer or blend of polymers and may comprise various additives, such as plasticisers, antiflame agents, pigments, and the like.
• the reinforcing glass fibres can be continuous, long, or short, and can be aligned following a given pattern or can be randomly distributed in the matrix.
• short, chopped glass fibres are generally blended with a polymeric melt in an extruder, a composite wire is drawn out of the extruder die and chopped to form short fibre reinforced polymeric pellets or granules, the two terms being considered herein as synonymous.
• Such composite pellets can then be melted again in the screw of an injection moulding machine or of an extruder to form final short glass fibre reinforced composite parts or continuous profiles, respectively.
• composite pellets reinforced with glass fibres according to the present invention are formed in an extruder as explained supra by blending a thermoplastic polyester, preferably PET of relatively low molecular weight. After formation of the composite pellets, these are subjected to a solid state post condensation process (SSPC). This sequence has revealed an unexpected rise in the hydrolysis resistance, compared with the usual sequence of subjecting the polyester polymer to the SSPC before compounding it with glass fibres.
• SSPC solid state post condensation process
• the SSPC step is preferably carried out by exposing the composite pellets to a temperature comprised between 1 60°C and 245°C, more preferably between 1 70°C and 240°C, and preferably in an inert gas atmosphere at a pressure of less than 1 0 kPa, more preferably less than 1 kPa, even more preferably less than 500 Pa.
• the stabilizer is preferably added in an amount between 0.1 and 3.0 wt.% , more preferably between 0.5 and 1 .5 wt.%, and should be selected from polycarbodiimide and/or an epoxy group containing stabilizer.
• the epoxy group containing stabilizer is preferably an epoxidized fatty acid ester or ether, preferably an epoxidized vegetable oil such as epoxidized soybean oil or talloil, or most preferably epoxidized linseed oil.
• nucleating agents are often necessary in PET, to increase the crystallization rate to values compatible with typical injection moulding process cycles. It is preferred that, if a nucleating agent is needed, it should be inorganic. Typical nucleating agents that can be added to a PET matrix reinforced with glass fibres according to the present invention are:
• metal oxides such as, titanium dioxide, magnesium dioxide, silicon dioxide, antimony trioxide, and/or
• silicates such as mica, kaolin or talc, and or
• the weight average particle size of the nucleating agent is preferably comprised between 0.5 and 5.0 ⁇ , more preferably between 0.7 and 2.0 ⁇ . It may be present in an amount of 0.02-1 .0 wt.%, more preferably of 0.05-0.2 wt.%.
• a sizing according to the present invention enhances the mechanical properties measured dry as moulded (DAM) or measured after ageing in moist conditions (i.e., conditions promoting hydrolysis).
• DAM dry as moulded
• Figure 1 shows graphs of un-notched Charpy test results (a) as a function of hydrolysis time and (b) after 72 h hydrolysis, measured on GF-PET composites according to the prior art (P.A.1 &P.A.2) and according to three embodi ments of the present invention (INV1 -3).
• Figure 2 shows graphs of the (a) tensile strength as a function of hydrolysis time, (b) tensile strength after 72 h hydrolysis, (c) tensile strain as a function of hydrolysis ti me, and (d) tensile strain after 72 h hydrolysis, measured on GF-PET composites according to the prior art (P.A.1 &P.A.2) and according to three embodi ments of the present invention (INV1 -3).
• Figure 3 shows a graph indicating the %-residual properties after 72 h hydrolysis relative to DAM for un-notched charpy, tensile strength and strain for the same samples as in Figures 1 &2.
• Figure 4 shows g raphs of the tensile strength as a function of hydrolysis ti me measu red on GF-PET composites with (a) glass fibres of the prior art (GF) and according to the present invention (GF*) for two different types of PET matrices, and (b) glass fibres accord ing to the present i nvention (GF*) with five d ifferent types of PET matrices.
• Figure 5 shows a graph of the tensile strength after 72 h hydrolysis of the samples represented in Figu re 4.
• the sizing composition of the present invention is a two part composition comprising a precu rsor and a binder, which are applied to the surface of the glass fi bres separately, in that order.
• the precursor comprises an aminosilane and a polymer or copolymer containing carboxylic acid and /or anhydride, both having a fu nctionality, F > 3.
• the binder comprises a multifunctional epoxy resin of functionality, F > 3, so that, upon crosslinking, it can form a tri-dimensional network.
• Preferred multifunctional epoxy resins are epoxy phenol novolac (EPN) or epoxy cresol novolac (ECN), which should be present in the dry composition in an amount comprised between 30 and 90 wt.%, more preferably between 50 and 70 wt.%.
• the aminosilane coupling agent preferably comprises monomeric or oligomeric ( ⁇ 6 units) silanes.
• Trialkoxysilanes are usually used as they permit to form a tri-dimensional network of Si-O-Si covalent bonds at the surface and around the surface of the glass fibres.
• Dialkoxysilanes decrease the amount of inter-silane chains covalent bonds, and form a hair like structure at the surface of the glass fibres.
• a tridimensional silane network is generally recognized as improving resistance to hydrolysis of the fibre by the formation of a densely crossilnked protective sheath around the fibres, it also tends to form fibre clusters by reaction between silanes of adjacent fibres, which a polymeric matrix melt cannot impregnate completely.
• dialkoxysilanes do not form a densely crossilnked protective sheath around the fibres, but facilitates impregnation of the fibre bundles and wetting of the individual fibres by a polymer melt.
• dialkoxysilanes With a lower polarity than trialkoxysilane, dialkoxysilanes reduce the hydrophilicity of the surface of the glass fibres which is believed to contribute to an enhancement of the resistance to hydrolysis to a level comparable to trialkoxysilane based silanes.
• trialkoxysilanes, dialkoxysilanes, and mixtures thereof can be used to form the silane coupling agent of the sizing, so that the crosslinking density around the glass fibres can be optimized at will.
• the silane based coupling agent should be present in an amount of 2 to 40 wt.% of total weight of sizing without water, preferably from 2.5 to 20.0 wt.%, more preferably from 5.0 to 1 5.0 wt.%.
• aminodialkoxysilane such as ⁇ -aminopropylmethyldiethoxysilane, N- -(Aminoethyl)- gam ma-am inopropylmethyldimethoxysi lane, N- -(Aminoethyl)-y-aminopropyl- methyldimethoxysilane, N- -(Aminoethyl)- ⁇ -aminoisobutylmethyldimethoxy-silane, ⁇ -aminopropylmethyldimethoxysilane, N- -(Aminoethyl)- ⁇ -aminopropyl- methyldiethoxysilane, and/or
• aminotrialkoxysilane such as ⁇ -aminopropyltriethoxysilane, y-aminopropyltri- methoxysilane, N- ⁇ -(Aminoethyl)- ⁇ -aminopropyl-trimethoxysilane, N- ⁇ -
• a polymer or co-polymer containing anhydride, in particular maleic anhydride and/or a carboxylic acid of functionality greater than 2 (F > 3) are used as crosslinker of the sizing composition.
• Maleic anhydride and multifunctional epoxy resins of functionality, F > 3, such as EPN or ECN, have been used individually as alternative crosslinkers in many sizing compositions disclosed in the documents cited in the BACKGROUND ART section supra. To our knowledge, they have, however, never been used in combination before. The reasons for this are very simple. First, they are considered as alternative crosslinkers, fulfilling the same function, so that there is no apparent reason to mix them.
• a (co-)polymer containing maleic anhydride which is soluble in water would generally form a highly unstable dispersion with any multifunctional epoxy resins, yielding a composition with limited reproducibility and shelf life.
• the latter problem is solved in the present invention by separating the maleic anhydride present in the precursor from the multifunctional epoxy resin present in the binder, such that the two components enter in contact with one another on the surface of the glass fibres.
• Examples of (co-)polymers containing anhydride comprise a copolymer ethylene-alt-maleic anhydride for example OC1 00LW.E from Michelman, copolymer butadiene-alt-maleic anhydride such as Maldene from Lindau Chemical, copolymer isobutylene-alt-maleic anhydride such as Isobam from Kuraray, copolymer acrylates-maleic anhydride such as Dicnal from DIC, and the like.
• Examples of (co-)polymers comprising carboxylic acid include polyacrylic acid such as Glascol C95 available from BASF. (Co-)polymers containing anhydride and carboxylic acid can be used alternatively or in combination.
• (Co-)polymers containing anhydride are preferred.
• the total amount of polymer or copolymer containing carboxylic acid and /or anhydride of functionality, F > 3 present in the dry composition is preferably comprised between 5.0 and 60.0 wt.%, more preferably between 1 5.0 and 30.0 wt.%.
• polyurethanes usually used in combination with either a maleic anhydride or an epoxy novolac in the sizing compositions of the prior art, are themselves quite sensitive to hydrolysis. This could explain why such sizing compositions offer a weaker protection against hydrolysis to composite materials.
• the maleic anhydride groups prevent the multifunctional epoxy resin from migrating into the polymeric matrix during the compounding or blending step in an extruder. It is important that as little multifunctional reactive components as possible migrate into the polymeric matrix, lest covalent bonds are formed in the matrix, which would increase the viscosity of the matrix. During the subsequent injection moulding operation, the shear forces generated increase with the viscosity of the blend, leading to the breakage of more glass fibres to the detriment of the mechanical properties of the thus injection moulded parts.
• a sizing according to the present invention preferably comprises a film former.
• a film former interacts with both the silane coupling agent and the matrix upon impregnation of the fibres. The film former must therefore be compatible with the matrix to be used.
• a film former protects the glass fibre from damage during processing (e.g., weaving, knitting, braiding, etc.) and promotes compatibility of the fibres with the matrix.
• Fibre reinforced composites are very sensitive to hydrolysis, and the mechanical properties of a composite exposed to hydrolysis conditions may drop by over 60% or more compared with the same properties measured dry as moulded (DAM). This substantial drop in mechanical properties upon exposure to hydrolysis conditions represents a major drawback of fibre reinforced composites. In many applications, such as outdoor applications in moist environments, or high temperature under the hood applications, the parts must be dimensioned taking account of these losses in mechanical properties, thus often becoming financially and technically (heavier) less competitive than alternative materials such as metals.
• Preferred film formers for a sizing according to the present invention comprise a polyurethane or a (meth-)acrylate polymer or co-polymer, or mixtures thereof.
• Other possible film formers preferably admixed to one of the foregoing film formers, but also usable alone, comprise: an epoxy resin emulsion, preferably based on any of an epoxy bisphenol A or epoxy bisphenol F; an epoxy ester resin ; an epoxy urethane resin; a polyamide; or mixtures thereof.
• the film former or mixture of film formers is preferably present in the precursor in an amount of 0.1 to 50.0 wt.% with respect to the total dry weight of the composition, more preferably 1 0.0 to 30.0 wt. %;.
• the sizing composition of the present inventions may comprise a number of additives, such as any of the following taken alone or in any combiation:
• pH adjusters such as bases, preferably ammonia or sodium hydroxide, and acids, preferably acetic acid or phosphoric acid,
• a non-ionic lubricant preferably a fatty alcohols ethoxylated or fatty acid monoester of polyethylene glycol, such as PEG 200 Monolaurate, PEG 600 Monooleate, PEG
• the non-ionic lubricant being preferably present in an amount of 0.1 to 30.0 wt.% solids, more preferably from 1 .0 to 20.0 wt.% solids, most preferably from 2.0 to 5.0 wt.% solids;
• a cationic lubricant such as a polyethyleneimine polyamide salt, and is preferably present in the size composition in an amount from 0.1 to 30.0 wt.% solids, more preferably from 1 .0 to 20.0 wt.% solids, most preferably from 2.0 to 5.0 wt.% solids,
• an antistatic agent such as a quaternary ammonium, a tetraethylammonium chloride, or lithium chloride, and is preferably present in an amount of 0.1 to 5.0 wt.% solids, preferably from 0.5 to 1 .5 wt.% solids.
• anti-foaming agents such as polysiloxane derivatives, the anti-foaming agent being preferably present in amount of less than 0.1 % of total weight of sizing without water,
• an isocyanate based cross-linker such as an isocyanurate, biuret, carbodiimide, the isocyanate based cross-linker being preferably present in amount of 0.1 to
• a boron-containing compound selected from the group consisting of boric acid, boron oxide, sodium tetraborate, potassium metaborate, potassium tetraborate, ammonium biborate, ammonium tetrafluoroborate, butylammonium tetrafluoroborate, calcium tetrafluoroborate, lithium fluoroborate, potassium tetrafluoroborate, sodium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetraethylammonium tetrafluoroborate and zinc tetrafluoroborate;
• the boron containing compound is preferably present in an amount of 0.1 to 50.0% with respect to the total dry weight of the composition, more preferably between 1 0.0 to 30.0 wt.%, most preferably between 2.5 and 1 0.0 wt.%;
• a hypophosphite containing compound such as a hypophosphite salt or phosphite containing compound such as: sodium hypophosphite, ammonium hypophosphite, calcium hypophosphites, trisnonylphenyl phosphite.
• the sizing composition can be applied to the surface of glass fibres as they are formed out of a bushing as an aqueous composition. It must be applied in two stages: a first coating station, generally comprising a roller contacting the fibres as they are running out of a bushing, for applying a precursor as discussed above, and a second station, applying a binder as discussed above.
• a first coating station generally comprising a roller contacting the fibres as they are running out of a bushing
• a second station applying a binder as discussed above.
• the precursor is usually applied to the fibres as they continuously run out of a bushing, whilst the binder is usually sprayed onto the chopped fibres
• the coated fibres are dried to evaporate the water to let the sizing composition react to form a sizing at the surface of the glass fibres.
• Sizing is generally applied to the surface of the glass fibres in an amount of 0.4 to 1 .2 wt.% with respect to the total weight of glass fibres, preferably between 0.6 and 1 .0 wt.%, more preferably between 0.8 and 09 wt.%. Unless otherwise indicated, all amounts of sizing and components in a sizing composition are expressed with respect to the total weight of sizing composition without any added water. In some cases, specifically indicated, as in the foregoing instance,
• Glass fibres according to the present invention, coated with a sizing as discussed above, are advantageously used to reinforce a polymeric matrix in composite materials.
• they can reinforce thermoplastic matrices in amounts comprised between 5 and 65 wt.%, preferably between 20 and 50 wt.%.
• the sizing of the present invention gives particularly good results with thermoplastic polyester matrices.
• Thermoplastic polyesters suitable for the present invention may be amorphous or a semi-crystalline.
• the thermoplastic polyester is a semi-crystalline polyester.
• Said semi-crystalline polyester is generally derived from at least one aromatic dicarboxylic acid or an ester-forming derivative thereof and at least one aliphatic, cycloaliphatic or aromatic diol, and includes homo- as well as copolymers.
• suitable aromatic diacids include terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, etc., with terephthalic acid being preferred.
• Suitable diols include alkylane diols, benzene diol, dihydroxyphenyl, naphthalene diol.
• Alkane diols like ethylene glycol, propylene glycol, 1 ,4-butane diol, neopentyl glycol, and cyclohexane dimethanol are preferred.
• These semi-crystalline polyesters may further comprise small amounts of, for example, aliphatic dicarboxylic acids, monofunctional alcohols and / or carboxylic acids and three or higher functional alcohols and/or carboxylic acids, provided that these polyesters remain melt-processable.
• the content of other monomers in these polyesters is below 20 wt.%, more preferably below 1 0 wt.%, even more preferably below 5 wt.%, relative to the total weight of the polyester, to ensure the semi-crystallinity of the polyester.
• Suitable thermoplastic polyesters that may be used in fibre reinforced composites according to the invention are, for example, polyalkyleneterephthalates, polyalkylene naphthalates, and polyalkylene bisbenzoates and any copolymers and any mixtures thereof. These polyesters can be derived from alkane diols and, respectively terephthalic acid, naphthalene dicarboxylic acid and 4,4'-diphenyldicarboxylic acid.
• the polyalkyleneterephthalate is poly(l ,4-cyclohexane-dimethylene terephthalate) (PCT) or a poly(alkylene terephthalate) based on an aliphatic diol with 2 to 6 carbon atoms, like polyethyleneterephthalate (PET), polytrimethyleneterephthalate (PTT), and poly(l ,4-butylene terephthalate) or simply called polybutylene terephthalate (PBT).
• Suitable poly(alkylene naphthalate)s include polyethylenenaphthalate (PEN) and polybutylenenaphthalate (PBN).
• Suitable polyalkylene bisbenzoates include polyethylenebisbenzoate (PEBB) and polybutylenebisbenzoate (PBBB).
• PEBB polyethylenebisbenzoate
• PBBB polybutylenebisbenzoate
• these semi-aromatic thermoplastic polyesters comprise a minority content of another dicarboxylic acid or diol.
• PET and PBT and any mixture or copolymer thereof are preferred. More preferably the thermoplastic polyester is PET.
• Glass fibres according to the present invention being coated with a sizing as described supra provide enhanced hydrolysis resistance to composite materials reinforced therewith, compared with glass fibre currently available on the market.
• resistance to hydrolysis also depends very much on the matrix.
• the matrix is a thermoplastic polyester which has been subjected to a solid state post condensation process after blending with the glass fibres.
• a solid state post condensation (SSPC) process makes it possible to produce in a first step a thermoplastic polyester having a relatively low molecular weight and thus a correspondigly low viscosity. Because of the low viscosity glass fibre breakage is reduced during mixing of the glass fibres with the molten polyester.
• the so obtained mixture may be granulated to form pellets and cooled down.
• the actual solid state post condensation is carried out to increase the molecular weight of the polyester by subjecting the glass fibre reinforced polymer composition to a heat-treatment, preferably at a temperature close to, but below the melting point of the polyester, under reduced pressure and/or a flow of an inert gas.
• the heat treatment preferably is carried out at a temperature between 1 60°C and 245°C, more preferably between 1 70°C and 240°C. The advantage of a higher temperature is that the time needed for obtaining the desired molecular weight is shorter.
• the inert gas atmosphere has a pressure of less than 1 0 kPa, more preferably less than 1 kPa, even more preferably less than 500 Pa.
• a lower pressure has the advantage that the required molecular weight is obtained in a shorter time. This allows a more efficient production process with a higher yield, without the need of extending the production installation.
• the SSPC of the polymer composition according to the invention may be carried out by any mode and in any apparatus suitable for that purpose.
• the process may suitably be carried out as a batch process, for instance in a tumble dryer, or as a continuous process, for instance in a moving bed reactor.
• a nucleating agent is often needed. This is especially true if the polyester is PET.
• a nucleating agent was found to be somewhat detrimental to the hydrolysis resistance of fibre reinforced polyester composites. It was discovered, however, that the drop in hydrolysis resistance of polyester composites comprising nucleating agents could be limited if an inorganic nucleating agent was used.
• inorganic nucleating agents include metal oxides, like for example titanium dioxide, magnesium dioxide, silicon dioxide, antimony trioxide, silicates like for example mica, kaolin and talc, as well as boron nitrides. Preferably talc is used.
• the weight average particle size of the nucleating agent is 0.5-5.0 ⁇ , more preferably 0.7-2.0 ⁇ .
• the concentration is preferably 0.02- 1 wt.%, more preferably 0.05- 0.2 wt.%. It was surprisingly discovered that a large increase in hydrolysis resistance of a glass fibre reinforced thermoplastic polyester composite could be obtained if the polyester matrix contains a stabilizer selected from a carbodiimide and/or an epoxy group containing stabilizer The addition of small amounts of such stabilizer even permits to compensate any drop in hydrolysis resistance caused by the use of a nucleating agent.
• the epoxy group containing stabilizer is preferably an epoxidized fatty acid ester or ether.
• epoxidized vegetable oils are suitable, such as epoxidized soybean oil or talloil, or most preferably epoxidized linseed oil. Mixtures of various of the foregoing epoxydized vegetable oils can be used.
• a stabilizer is preferably present in an amount of 0.1-5.0 wt.%, more preferably of 0.5-2.0 wt.% with respect to the total weight of matrix. Good results are obtained if the epoxidized stabilizer contains between 0.1 and 5 wt.% of oxirane oxygen, preferably between 0.3 and 5 wt. %.
• the stabilizer -preferably an epoxidized vegetable oil- is preferably dusted or sprayed onto the surface of the granulated composition after the SSPC step is completed. In this way no unwanted reactions between the epoxidized vegetable oil or the epoxidized modified vegetable oil can take place during the SSPC step.
• Figures 1 to 3 graphically illustrate mechanical tests results carried out on 35 wt.% chopped glass fibre reinforced PET composites using glass fibres of the prior art and fibres according to the present invention. All the samples comprised the same PET matrix: a PET homopolymer of relative viscosity of 1.34, measured according to ISOl 628-5 on 1 g polymer dissolved in 125 g dichloroacetic acid at 25°C.
• the glass fibres of the prior art samples P.A.I were glass fibres available on the market from PPG (ChopVantageTM HP 3786).
• the composition of the prior art glass fibres P.A.I is not known but it is indicated as being optimized for reinforcing PET.
• A.2 and the ones according to the present invention were sized with different sizing compositions as listed in Table 1.
• Glass fibres and PET were blended using a lab size ZSK30 twin-screw extruder from Werner&Pfeiffer with a barrel temperature of 260-310 °C.
• the PET polymer was dried before use (moisture content below 0.01%).
• the glass fibres were introduced via a side-feeder into the polymer melt. Extruded strands were cooled in water and granulated to form granules (or pellets) of PET reinforced with 35 wt.% of glass fibres.
• Test samples were produced by injection moulding the thus produced glass fibre-PET g ranules.
• the samples were tested dry as moulded (DAM) and after 24, 48, 72 h accelerated ageing in water steam (500 ml demineralised water) at 1 1 0°C at a pressure of 1 .4 bar (1 40 kPa) in a pressure vessel. Each mechanical value is the average over ten repetitions of the test.
• Table 1 compositions of the sizings on glass fibres of samples INVl -3 represented in Figures 1 to 3.
• Silane ⁇ -aminopropyl triethoxysilane, Al 1 00 from Momentive.
• EMA copolymer of ethylene maleic anhydride OC1 00LW.E from Michelman.
• EPN Epoxy phenol novolac, Epirez 5054 from Momentive.
• PU406 polyether based polyurethane from Bayer.
• Figu re 1 (a) plots the results as a function of exposure time to hydrolysis conditions, and Figure 1 (b) represents the UN- Charpy values measured after 72 h exposure to hydrolysis conditions, correspond ing to the last points on the right hand side of Figure 1 (a).
• Figure 2 represents the tensile tests values measured according to ISO 527-2 on dog bone samples of the same composite materials as discussed with respect to Figure 1 .
• the tensile strength measured DAM is not substantially affected by the type of sizing used (cf. Figure 2(a)).
• the tensile strength after hydrolysis is much improved with the sizing according to the present invention compared with the commercial composite P.A. I , and a little better than P.A.2 sample, with 5 to almost 1 0 MPa higher strength values for the inventive samples than for the P.A.2 after 72 h hydrolysis (cf. Figure 2(b)).
• Figure 3 shows in the last two groups of columns in the right hand side, that the residual tensile strength and strain after 72 h is much inferior for the commercial product P.A. I than for the inventive samples INV1 -3 which have values comparable with the ones of P.A.2 sample.
• Example 1 and Figu res 1 to 3 demonstrate the advantageous effect of sizings according to the present invention on the mechanical properties measured both DAM and after exposure to accelerated hysdrolysis conditions on composites reinforced with various embodi ments of g lass fi bres according to the present invention and of the prior art reinforcing the same PET matrix.
• Example 2 wil l show how the increase in properties of the inventive composites can further be enhanced by mod ifying the matrix to adapt it to the sizing .
• Table 2 compositions of the samples of Example 2 and Figures 4&5
• GF* is a glass fibre sized with a composition according to INV1 (cf. Table 1 )
• (2) GF is a commercial glass fibre ChopVantageTM HP 3786, available from PPG Industries Fibre Glass.
• Glass fi bres and PET were blended using a ZE40A UTX twin-screw extruder from Berstorff with a barrel temperature of 260-31 0 °C, screw speed of 300 RPM and a yield of 1 80 kg / hour.
• the PET base polymer was dried before use (moistu re content below 0.01 %).
• Com ponents such as PET, nucleating agent and mould release agent (0.35 wt.% of Carnauba wax available from Paramelt) were dosed to the hopper as a pre-blend.
• the glass fibres were introduced via a side-feeder into the polymer melt.
• Extruded strands were cooled in water and granulated to form pellets of PET reinforced with 35 wt.% of glass fibres.
• Some of the glass fibre-PET pellets were heat treated according to a preferred embodiment of the present invention to provoke solid state post condensation (SSPC).
• SSPC was performed in a 1 00 litre tumble-drier unit. The drier was charged with 25 kg glass fibre-PET granules and pressure was reduced to 80 mbar (8 kPa), vented with pure, dry nitrogen and temperature raised initially to 1 20°C. After 1 hour at 1 20°C pressure was reduced to 4 mbar and temperature was raised to 1 35°C.
• a stabilizer was added to the granule surface of some of the samples after the SSPC treatment.
• the stabilizer was epoxydized linseed oil (ELO) added to the glass fibre-PET pellets in a tumble-drier at 23°C under a nitrogen flow, and then heated up to 1 40°C while rotating. After 2 hours the material was cooled down to room temperature.
• ELO epoxydized linseed oil
• Tensile test dogbone testbars according to the ISO 527- 1 A standard were injection moulded from pre-dried (1 0 hours at 1 20°C under vacuum with nitrogen flow) granules on an Arburg 1 1 0 injection moulding machine, with temperature settings 260-270°C, and mould temperature of 1 40°C. Some of the tensile testbars were exposed to accelerated hydrolysis conditions in a hot steam atmosphere in an autoclave at a temperature of 1 1 0°C and a pressure of 1 .4 bar for various times: 24, 48, and 72 hours.
• Figure 4(a) illustrates the tensile strength as a function of hydrolysis time for various samples according to the invention (black and white circles) and to the prior art (black and white squares), wherein glass fibre-PET granules underwent only an SSPC step (cf. white symbols) and were dusted with 0.5 wt.% ELO after SSPC (black symbols). It can be seen that the DAM properties are approximately constant for all the samples represented in the Fig ure. Tensile strength after 72 h hyd rolysis, however, is much superior for the composite samples reinforced with glass fibres according to the present invention (cf. circles), than for the prior art samples (cf. squares) confirming the results discussed in Example 1 .
• Figure 4(b) represents the tensile strength as a fu nction of hydrolysis time for samples all reinforced with g lass fi bres according to the present invention, and with the same PET matrix, but the latter was treated according to various preferred embodiments.
• talc was used, yielding a 25% drop of the tensile strength after 72 h hyd rolysis, as can be seen by comparing samples "I NV GF-(PET+SSPC+0.5 ELO)" and "INV GF- (PET+SSPC+0.5 ELO+talc)" in Figure 5 , from 1 53 MPa down to 1 1 4 MPa.
• Replacing talc by an organ ic nucleating agent, viz., sod ium benzoate dropped the mechanical properties even lower down to a tensile strength of 74 MPa (not shown in the Fig ures). For this reason, it is preferred that, if required, a nucleating agent should preferably be selected among inorgan ic compounds.
• the d rop in tensile strength after hydrolysis caused by the addition of a nucleating agent can be compensated totally by increasing the amount of stabilizer as can be seen in Figure 5 by comparing the last two shaded columns on the right hand side both comprising talc as n ucleating agent and differing in the amount of ELO, wherein the residual tensile strength rises from 1 1 4 MPa with samples comprising 0.5 wt.% ELO to 1 55 MPa (+ 36%) with samples comprising 1 .3 wt.% ELO.

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