SIZING AGENTCOMPRISING FUNCTIONALIZED POLYOLEFINS

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT/EP2023/074653, filed Sep. 7, 2023, which claims the benefit of European Application No. 22195200.5, filed Sep. 12, 2022, both of which are incorporated by reference in their entirety herein.

FIELD OF INVENTION

The invention relates to a sizing agent and to the use of the sizing agent as a coating on a reinforcing fiber. The invention further relates to a sizing composition comprising the sizing agent. The invention further relates to a sized reinforcing fiber comprising a reinforcing fiber being coated with the sizing agent and to a process for preparing the sized reinforcing fiber. In addition, the invention further relates to a polymer composite comprising the sized reinforcing fiber.

BACKGROUND

Fiber reinforced polymer composites are often used in preparing molded articles such as automotive and aerospace components, consumer goods and electrical components, which require such molded articles to have a certain desired level of mechanical properties such as impact and tensile strength. Typically such polymer composites have a polymeric matrix in which the reinforcing fiber is dispersed. A possible factor for the improved mechanical performance of any composite is due to the efficient load transfer from the matrix to the fiber, when the composite is subjected to a certain force. However, the extent to which the desired mechanical properties are achieved is governed, at least in part, by the degree of compatibility or adhesion between the reinforcing fiber the polymer matrix. Further, as reinforcing fibers such as carbon fibers, have low ductility and are usually brittle, the fibers tend to generate fuzz or fiber breakage as a result of mechanical abrasion during processing, which adversely affects the processability of the fibers and the quality of the reinforced article.

One of the ways to reduce fuzz and improve the interfacial compatibility between the inorganic reinforcing fiber and the organic polymer matrix is by coating the reinforcing fiber with a sizing agent. Usually, the coating is in the form of a thin coating layer (typically of ˜100 nm) known as sizing, which forms the interphase between the fiber and matrix. Accordingly, a sized fiber has an improved compatibility with the resin matrix in which the fibers are dispersed along with improved processability. However, in certain instances, the reinforcing fiber after being sized may lose out on its tensile properties, which may adversely affect subsequent processing and handling of the reinforcing fiber.

In the past, various attempts have been made to develop suitable sizing agents. For example, the patent EP1403420B1 (“EP patent”) claims a compound having at least one epoxy group per molecule, an anionic surfactant having an ammonium ion as a counter ion, a nonionic surfactant, with wherein the nonionic surfactant (C) is contained at 1/50 to 1/2 (weight ratio) relative to the anionic surfactant (B). The EP patent indicates that by having such a limitation of the weight ratio of the surfactants, the reactivity of the ammonium ion with respect to the epoxy group can be decreased and as a result, changes over time in carbon fibers adhered with sizing agent can be significantly inhibited. Although, the sizing agent described in the EP patent is promising, the teachings are limited to only epoxy based sizing agents, using only a certain specific class of anionic surfactants combined at a specific ratio with a non-ionic surfactants.

JP 635263 discloses a sizing agent for a carbon fiber, which can impart a sufficient strength to a carbon fiber composite material while suppressing the use of an emulsifier and a basic material by using an acid-modified polyolefin that is easily emulsified. US 2014/0227516 discloses a sizing agent for carbon fiber used for reinforcing a thermoplastic matrix resin, the sizing agent essentially comprising a polymer component having a glass transition temperature of at least 20° C. and exhibiting no endothermic peaks indicating an endothermic heat of fusion due to crystalline melting of at least 3 J/g in a determination with a differential scanning calorimeter; wherein the weight ratio of the polymer component constitutes from 10 to 100 wt. % of the nonvolatile components of the sizing agent; wherein the polymer component is at least one component selected from the group consisting of an aromatic polyester resin, aromatic polyester-polyurethane resin and amine-modified aromatic epoxy resin; wherein the aromatic polyester-polyurethane resin is a polymer produced by addition polymerization of an aromatic polyester polyol and polyisocyanate; wherein the amine-modified aromatic epoxy resin is a reaction product of an aromatic epoxy compound and hydroxyl-group-containing amine compound with the ratio of the hydroxyl-group-containing amine compound ranging from 1.0 to 2.0 mol equivalent to the epoxy groups of the aromatic epoxy compound.

US 2012/0238688 discloses a carbon fiber-reinforced resin composition, comprising (A) a polyolefin resin, (B) an acid-modified polyolefin resin, and (C) a modified carbon fiber with an adhesion amount of an amino group-containing modified polyolefin resin of from 0.2 to 5.0 mass %, wherein a mass ratio of (A):(B) is from 0:100 to 99.5:0.5, and a mass ratio [(A)+(B)]:(C) is from 40:60 to 97:3.

CN 106884330 discloses an emulsion-type sizing agent for a carbon fiber, and a preparation method and an application of the emulsion-type sizing agent. The method comprises the steps of firstly dissolving polyurethane resin into a volatile organic solvent at room temperature, adding a surfactant, mixing evenly and preparing a main slurry solution; dispersing the surfactant into deionized water to prepare emulsifying water; dropwise adding the emulsifying water to the main slurry solution until the main slurry solution is subjected to phase inversion; and finally adding all remaining emulsifying water to the main slurry solution and continuously stirring to obtain a final product. The final product is not solidified in water and is uniform in particle sizes and good in stability and the particle sizes are 100-200 nm; the emulsion-type sizing agent can be stored in a room-temperature drying condition for 6 months; and the heat-resistance temperature can reach 280-300° C.

Therefore, it is an object of the present invention to provide a sizing agent imparting improved fiber-matrix compatibility in a polymer composite. Another object of the present invention is to provide a sizing composition having improved emulsion stability. Yet another object of the present invention is to provide a sized reinforcing fiber, having improved processability while retaining the desired mechanical properties.

SUMMARY

Accordingly, the one or more objectives of the present invention is achieved by a sizing agent comprising:

• • at least one functionalized polyolefin polymer;
  • at least one base compound, wherein the base compound is selected from the group consisting of:
    • i. an inorganic base;
    • ii. an organic base; and
    • iii. any combination thereof;
  • at least one non-ionic surfactant; and
  • at least one ionic surfactant.

The total weight of functionalized polyolefin polymer, base compound, non-ionic surfactant and ionic surfactant is 100 wt. %. Preferably, an aqueous solution comprising the 0.01 wt. % to 40.0 wt. %, preferably from 0.1 wt. % to 30.0 wt. %, preferably from 0.1 wt. % to 25.0 wt. %, preferably from 1.0 wt. % to 10.0 wt. %, preferably from 1.0 wt. % to 6.0 wt. %, preferably from 2.0 to 5.0 wt. %, of the sizing agent has a pH in the range of greater than 7.0 to 12.0, preferably from 7.2 to 11.0, preferably from 8.5 to 11.0, preferably from 8.5 to 10.5.

Preferably, (a) the functionalized polyolefin polymer is present in an amount from 50.0 wt. % to 90.0 wt. %.; (b) the non-ionic surfactant is present in an amount from 10.0 wt. % to 25.0 wt. %; (c) the ionic surfactant is present in an amount from 0.5 wt. % to 5.0 wt. %; (d) the inorganic base, if present, is present in an amount from 1.0 wt. % to less than 12.5 wt. %; (e) the organic base, if present, is present in an amount from 8.0 wt. % to 30.0 wt. %; based on the total weight of the sizing agent, provided the sizing agent comprises any one of the organic base or the inorganic base. Total weight of (a)-(e) is 100 wt. %.

Preferably, (a) the functionalized polyolefin polymer is present in an amount from 55.0 wt. % to 85.0 wt. %.; (b) the non-ionic surfactant is present in an amount from 15.0 wt. % to 25.0 wt. %; (c) the ionic surfactant is present in an amount from 1.0 wt. % to 3.0 wt. %; (d) the inorganic base, if present, is present in an amount from 2.0 wt. % to 10.0 wt. %; (e) the organic base, if present, is present in an amount from 12.0 wt. % to 18.0 wt. %; based on the total weight of the sizing agent, provided the sizing agent comprises any one of the organic base or the inorganic base. Total weight of (a)-(e) is 100 wt. %.

Preferably, (a) the functionalized polyolefin polymer is present in an amount from 60.0 wt. % to 75.0 wt. %.; (b) the non-ionic surfactant is present in an amount from 15.0 wt. % to 20.0 wt. %; (c) the ionic surfactant is present in an amount from 1.0 wt. % to 3.0 wt. %; (d) the inorganic base, if present, is present in an amount from 2.0 wt. % to 10.0 wt. %; (e) the organic base, if present, is present in an amount from 12.0 wt. % to 18.0 wt. %; based on the total weight of the sizing agent, provided the sizing agent comprises any one of the organic base or the inorganic base. Total weight of (a)-(e) is 100 wt. %.

Preferably, (a) the functionalized polyolefin polymer is present in an amount from 65.0 wt. % to 75.0 wt. %; (b) the non-ionic surfactant is present in an amount from 15.0 wt. % to 20.0 wt. %; (c) the ionic surfactant is present in an amount from 1.0 wt. % to 3.0 wt. %; (d) the inorganic base, if present, is present in an amount from 3.0 wt. % to 8.0 wt. %; (e) the organic base, if present, is present in an amount from 12.0 wt. % to 18.0 wt. %; based on the total weight of the sizing agent, provided the sizing agent comprises any one of the organic base or the inorganic base. Total weight of (a)-(e) is 100 wt. %.

Preferably, the sizing agent comprises either an inorganic base or an organic base. Preferably, when the sizing agent comprises an inorganic base, the sizing agent is free of an organic base. Preferably, when the sizing agent comprises an organic base, the sizing agent is free of an inorganic base. Preferably the sizing agent comprises only an inorganic base and accordingly preferably the sizing agent does not comprise, i.e. is free of, an organic base.

DETAILED DESCRIPTION

The expression “sizing agent” as used throughout this disclosure means a coating composition suitable to be applied on a reinforcing fiber. The expression “sized” as used throughout this disclosure means a reinforcing fiber coated with a sizing agent.

Advantageously, the inventors found that when reinforcing fibers are sized with the sizing agent of the present invention, not only do the reinforcing fibers retain their mechanical properties but also demonstrate improved fiber-matrix compatibility when such sized fibers are dispersed in a polymer matrix.

Accordingly, in an aspect of the present invention, the invention relates to the use of the sizing agent of the present invention, as a coating on at least a portion of a reinforcing fiber for improving the adhesion between the reinforcing fiber and a polymer matrix in which the reinforcing fiber is dispersed.

Functionalized Polyolefin Polymer

The sizing agent comprises at least one functionalized polyolefin. The expression “functionalized polyolefin polymer” means a polyolefin, which has one or more polar functional group attached to a polyolefin polymer via a covalent link. Alternatively, the expression “functionalized polyolefin polymer” may refer to a polyolefin copolymer where an olefin monomer is copolymerized under pressure with one or more monomer having a polar functional group. Polar functional group may include chemical groups such as an anhydride group, an ester group, an epoxy group, an acyl group, a carboxylic acid group or an amide group.

The functionalized polyolefin polymer may be selected from the group consisting of maleic anhydride grafted polyolefin, maleic anhydride based polyolefin co-polymers, maleic anhydride based polyolefin terpolymers, glycidyl (meth)acrylate based polyolefin copolymer, glycidyl (meth)acrylate grafted polyolefin, itaconic anhydride grafted polyolefin, citraconic anhydride grafted polyolefin, allylsuccinic anhydride grafted polyolefin, and combinations thereof.

Preferably the functionalized polyolefin polymer comprises or consists of a maleic anhydride grafted polyolefin. The maleic anhydride grafted polyolefin may be selected from the group consisting of maleic-anhydride grafted polyethylene, maleic-anhydride grafted polypropylene, maleic-anhydride grafted copolymer of ethylene and propylene, maleic anhydride grafted copolymer of ethylene and an alpha-olefin having 4 to 10 carbon atoms, maleic anhydride grafted terpolymers of propylene-ethylene and an alpha-olefin having 4 to 10 carbon atoms, and any combinations thereof.

Preferably the functionalized polyolefin polymer is maleic-anhydride grafted polypropylene. The maleic-anhydride may be present in an amount from 0.01 wt. % to 10.0 wt. %, preferably from 0.1 wt. % to 7.0 wt. %, preferably from 0.1 wt. % to 5.0 wt. %, based on the total weight of the functionalized polyolefin polymer.

The functionalized polyolefin polymer may be present in an amount from 50.0 wt. % to 90.0 wt. % based on the total weight of the sizing agent. Preferably the functionalized polyolefin polymer is present in an amount from 55.0 wt. % to 85.0 wt. %, preferably from 60.0 wt. % to 80.0 wt. %, preferably from 60.0 wt. % to 75.0 wt. %, preferably from 65.0 wt. % to 75.0 wt. %, preferably from 60.0 wt. % to 70.0 wt. %, preferably from 68.0 wt. % to 75.0 wt. %, preferably from 62.0 wt. % to 68.0 wt. %, based on the total weight of the sizing agent.

Base Compound

The base compound is selected from an inorganic base or an organic base, or any combination thereof. Preferably the base compound is selected from any one of an inorganic base or an organic base.

Preferably, the base compound is selected from any one of:

• • the inorganic base, present in an amount from 1.0 wt. % to less than 12.5 wt. %, preferably 1.0 wt. % to less than 12.0 wt. %, preferably from 2.0 wt. % to 10.0 wt. %, preferably from 3.0 wt. % to 8.0 wt. %, based on the total weight of the sizing agent; or
  • the organic base, present in an amount from 8.0 wt. % to 30.0 wt. %, preferably from 10.0 wt. % to 20.0 wt. %, preferably from 12.0 wt. % to 18.0 wt. %, based on the total weight of the sizing agent.

Preferably, wherein the sizing agent of the present invention comprises or consists of,

• • the inorganic base selected from the group consisting of potassium hydroxide, sodium hydroxide, cesium hydroxide, barium hydroxide, ammonium hydroxide, and any combinations thereof; and/or
  • the organic base selected from the group consisting of N,N-dimethyl aminoethanol (DMAE), 2-(methylamino) ethanol, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, 2-(butylamino)ethanol, N-butyldiethanolamine, N-tert-butyldiethanolamine, triisopropanolamine, bis(2-hydroxypropyl)amine, N,N-bis(2-hydroxypropyl)ethanolamine, 1-[N,N-bis(2-hydroxyethyl)amino]-2-propanol, N,N,N′,N′-tetrakis(2-hydroxyethyl)ethylenediamine, N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylene diamine, morpholine, diethanol amine, diethylmethanol amine, N,N-dimethyl-dihydrosphingosine, and any combinations thereof.

Preferably the inorganic base comprises or consists of potassium hydroxide and the organic base comprises or consists of N,N-dimethyl aminoethanol (DMAE).

Non-Ionic Surfactant

The non-ionic surfactant may be selected from the group consisting of a linear or branched alkylphenol ethoxylate, alkylphenol, polyoxyalkylene alylphenylether, octylphenoxy poly(ethyleneoxy)ethanol, sorbitan oleate, polyethylene glycol sorbitan monooleate, polyethylene glycol sorbitan monolaurate, t-octylphenoxypolyethoxyethanol, polyoxyethylene (10) isooctylcyclohexyl ether, alpha-[3,5-Dimethyl-1-(2-methylpropyl)hexyl]-omega-hydroxypolyloxy-1,2-ethanediyl, polyethylene glycol monoalkyl ether, and any combinations thereof. Preferably the non-ionic surfactant is a linear or branched alkylphenol ethoxylate. Preferably the linear or branched alkylphenol ethoxylate comprises or consists of polyoxyethylene (9) nonylphenylether branched.

The non-ionic surfactant may be present in an amount from 10.0 wt. % to 25.0 wt. % based on the total weight of the sizing agent. Preferably, the non-ionic surfactant is present in an amount from 10.0 wt. % to 20.0 wt. %, preferably in an amount from 15.0 wt. % to 25.0 wt. %, preferably in an amount from 15.0 wt. % to 20.0 wt. %, based on the total weight of the sizing agent.

Ionic Surfactant

The ionic surfactant may comprise as a counter ion an alkali-metal ion or an alkali-earth metal ion or an ammonium ion. Preferably, the ionic surfactant comprises an alkali-metal ion.

The ionic surfactant may be selected from the group consisting of alkali metal salt of dioctyl sulphosuccinate, alkali metal salt of 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxo-2-butanesulfonate, alkali metal salt of dicyclohexyl sulfosuccinate, alkali metal salt of dihexyl sulfosuccinate, alkali metal salt of dibutyl sulfosuccinate, alkali metal salt of bis(2-ethylhexyl) sulfosuccinate, alkali metal salt of dodecylbenzenesulfonate, 4-dodecylbenzenesulfonic acid, alkali metal salt of sulfosuccinic acid, alkali metal salt of poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether, alkali metal salt of dodecyl sulfate, cholesteryl sodium sulfate, alkali metal salt of desoxycholic acid, and any combinations thereof.

Preferably the ionic surfactant comprises or consists of an alkali metal salt of 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxo-2-butanesulfonate. Preferably, the alkali metal salt comprises or consists of a sodium salt of 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxo-2-butanesulfonate.

The ionic surfactant may be present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %, based on the total weight of the sizing agent. The inventors surprisingly found that the use of the ionic surfactant did not result in any emulsion instability as no gel formation is observed even when the sizing composition once formed is stored for more than one month.

The sizing agent may be formulated such that the weight ratio of the non-ionic surfactant to ionic surfactant is greater than 1.0. Preferably, the weight ratio of the non-ionic surfactant to ionic surfactant ranges from 2.0 to 50.0, preferably from 3.0 to 20.0.

Compound (A)

In an aspect of the invention, the sizing agent may comprise at least one compound (A) selected from the group consisting of sodium metabisulfite, potassium metabisulfite, sodium hypochlorite, calcium hypochlorite, monochloramine, trichloroisocyanuric acid, sodium benzoate, 4-hexylresorcinol, chloroxylenol, and any combinations thereof. Preferably, the at least one compound (A) is present in an amount from 0.1 wt. % to 1.0 wt. %, preferably in an amount from 0.5 wt. % to 1.0 wt. %, based on the total weight of the sizing agent.

Sizing Agent

The sizing agent of the present invention is formulated to comprise at least one functionalized polyolefin polymer, at least one base compound, least one non-ionic surfactant, at least one ionic surfactant and optionally at least one compound (A). The base compound may be combined with the functionalized polyolefin polymer, the non-ionic surfactant and the ionic surfactant, each present at a specific proportion, in order to arrive at the sizing agent of the present invention.

The sizing agent may comprise:

• • at least one functionalized polyolefin polymer present in an amount from 50.0 wt. % to 90.0 wt. %;
  • at least one base compound, wherein the base compound is selected from the group consisting of:
    • i. an inorganic base;
    • ii. an organic base; and
    • iii. any combination thereof;
  • at least one non-ionic surfactant present in an amount from 10.0 wt. % to 25.0 wt %; and
  • at least one ionic surfactant present in an amount from 0.5 wt. % to 5.0 wt. %;
  • based on the total weight of the sizing agent; wherein the inorganic base if present, is present in an amount of from 1.0 wt. % to less than 12.5 wt. %, based on the total weight of the sizing agent and wherein the organic base present if present, is present in an amount from 8.0 wt. % to 30.0 wt. %, based on the total weight of the sizing agent.

The sizing agent may comprise:

• • the functionalized polyolefin polymer present in an amount from 50.0 wt. % to 90.0 wt. %, preferably from 55.0 wt. % to 85.0 wt. %, preferably from 60.0 wt. % to 80.0 wt. %, preferably from 60.0 wt. % to 75.0 wt. %, preferably from 65.0 wt. % to 75.0 wt. %, preferably from 60.0 wt. % to 70.0 wt. %, preferably from 68.0 wt. % to 75.0 wt. %;
  • the non-ionic surfactant present in an amount from 10.0 wt. % to 25.0 wt. %, preferably from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 25.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %; and
  • the ionic surfactant present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %;
  • based on the total weight of the sizing agent.

The proportion of the functionalized polyolefin polymer and the base compound may be adjusted to provide the desired emulsion stability. Preferably, when the base compound is an inorganic base, the weight ratio of the inorganic base to the functionalized polyolefin polymer present in the sizing agent ranges from 0.01 to 0.24, preferably from 0.04 to 0.12, preferably from 0.06 to 0.1. Preferably when the base compound is an organic base the weight ratio of the organic base to the functionalized polyolefin polymer present in the sizing agent ranges from 0.08 to 0.6, preferably from 0.13 to 0.36, preferably from 0.16 to 0.28.

Preferably, the sizing agent comprises:

• • the functionalized polyolefin polymer, present in an amount from 50.0 wt. % to 90.0 wt. %, preferably from 55.0 wt. % to 85.0 wt. %, preferably from 60.0 wt. % to 80.0 wt. %, preferably from 60.0 wt. % to 75.0 wt. %, preferably from 65.0 wt. % to 75.0 wt. %, preferably from 60.0 wt. % to 70.0 wt. %, preferably from 68.0 wt. % to 75.0 wt. %;
  • the base compound, wherein the base compound is selected from any one of:
    • the inorganic base, present in an amount from 1.0 wt. % to less than 12.5 wt. %, preferably from 1.0 wt. % to less than 12.0 wt. %, preferably from 2.0 wt. % to 10.0 wt. %, preferably from 3.0 wt. % to 8.0 wt. %; or
    • the organic base, present in an amount from 8.0 wt. % to 30.0 wt. %, preferably from 10.0 wt. % to 20.0 wt. %, preferably from 12.0 wt. % to 18.0 wt. %;
  • the non-ionic surfactant present in an amount from 10.0 wt. % to 25.0 wt. %, preferably from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 25.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %; and
  • the ionic surfactant present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %;
  • based on the total weight of the sizing agent.

Sizing Agent Comprises an Inorganic Base

It is preferred that the sizing agent comprises an inorganic base and wherein:

• • the functionalized polyolefin polymer is present in an amount from 65.0 wt. % to 75.0 wt. %, preferably from 68.0 wt. % to 75.0 wt. %;
  • the inorganic base is present in an amount from 2.0 wt. % to 10.0 wt. %, preferably from 3.0 wt. % to 8.0 wt. %;
  • the non-ionic surfactant is present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %;
  • the ionic surfactant is present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %; and
  • the compound (A) is present in an amount from 0.1 wt. % to 1.0 wt. %, preferably from 0.1 wt. % to 0.8 wt. %;
    based on the total weight of the sizing agent.

It is preferred that the sizing agent comprises an inorganic base and wherein:

• • the functionalized polyolefin polymer is maleic-anhydride grafted polypropylene, present in an amount from 65.0 wt. % to 75.0 wt. %, preferably from 68.0 wt. % to 75.0 wt. %;
  • the inorganic base is potassium hydroxide, present in an amount from 2.0 wt. % to 10.0 wt. %, preferably from 3.0 wt. % to 8.0 wt. %;
  • the non-ionic surfactant is polyoxyethylene (9) nonylphenylether branched, present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %;
  • the ionic surfactant is an alkali metal salt of 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxo-2-butanesulfonate, present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %; and
  • the compound (A) is sodium metabisulfite present in an amount from 0.1 wt. % to 1.0 wt. %, preferably from 0.1 wt. % to 0.8 wt. %;
    based on the total weight of the sizing agent.

Sizing Agent Comprises an Organic Base

It is preferred that the sizing agent comprises an organic base and wherein:

• • the functionalized polyolefin polymer is present in an amount from 60.0 wt. % to 70.0 wt. %, preferably from 62.0 wt. % to 68.0 wt. %;
  • the organic base is present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 12.0 wt. % to 18.0 wt. %;
  • the non-ionic surfactant is present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %;
  • the ionic surfactant is present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %; and
  • the compound (A) is present in an amount from 0.1 wt. % to 1.0 wt. %, preferably from 0.1 wt. % to 0.8 wt. %;
    based on the total weight of the sizing agent.

It is preferred that the sizing agent comprises an organic base and wherein:

• • the functionalized polyolefin polymer is maleic-anhydride grafted polypropylene present in an amount from 60.0 wt. % to 70.0 wt. %, preferably from 62.0 wt. % to 68.0 wt. %;
  • the organic base is N,N-dimethyl aminoethanol (DMAE), present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 12.0 wt. % to 18.0 wt. %;
  • the non-ionic surfactant is polyoxyethylene (9) nonylphenylether branched present in an amount from 10.0 wt. % to 20.0 wt. %, preferably from 15.0 wt. % to 20.0 wt. %;
  • the ionic surfactant is an alkali metal salt of 1,4-bis[(2-ethylhexyl)oxy]-1,4-dioxo-2-butanesulfonate, present in an amount from 0.5 wt. % to 5.0 wt. %, preferably from 1.0 wt. % to 3.0 wt. %; and
  • the compound (A) is sodium metabisulfite present in an amount from 0.1 wt. % to 1.0 wt. %, preferably from 0.1 wt. % to 0.8 wt. %;
    based on the total weight of the sizing agent.

Sizing Composition

In some aspects of the invention, the invention is directed to a sizing composition, comprising (i) the sizing agent in accordance with the present invention, and (ii) a dispersion medium, wherein the sizing composition has a pH of greater than 7.0, preferably at least 7.2, preferably at least 8.5. Preferably, the sizing agent is dispersed in the dispersion medium. Preferably, the sizing composition is an emulsion having the sizing agent dispersed in the dispersion medium.

The sizing composition may have a pH in the range of greater than 7.0 to 12.0, preferably from 7.2 to 11.0, preferably from 8.5 to 11.0, preferably from 8.5 to 10.5. The pH of the sizing composition may be controlled by using a suitable proportion of the functionalized polyolefin polymer and the base compound. The inventors found that a suitable control of pH imparted the desired emulsion stability to the sizing composition and influenced the properties and performance of the sizing agent.

It is preferred that when the base compound is an organic base, the pH of the sizing composition is maintained in the range from 8.5 to 10.5. Alternatively, it is preferred that when the base compound is an inorganic base, the pH of the sizing composition is maintained in the range from 7.2 to 8.5.

The dispersion medium may be a protic solvent. Non-limiting examples of protic solvent include aqueous solvent, or at least one organic alcohol having 1-20 carbon atoms. Preferably the at least one organic alcohol is selected from methanol, ethanol, n-propanol, i-propanol, n-butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, and decanol.

Preferably, the dispersion medium is an aqueous solvent. Preferably the sizing composition comprises the sizing agent as disclosed herein and a dispersion medium comprising an aqueous solvent, wherein the pH of the sizing composition has a pH of greater than 7.0.

The aqueous solvent may comprise water and a water-miscible solvent. Water-miscible solvent may be selected from methanol, ethanol, n-propanol, i-propanol, dioxane, tetrahydrofuran, acetone, acetonitrile and combinations thereof. The volume ratio of water:water miscible solvent may vary from 99:1 to 10:90, or from 99:1 to 50:50, or from 99:1 to 70:30. Preferably, the aqueous solvent comprises entirely of water, preferably de-ionized water.

The sizing agent may be present in an amount from 0.01 wt. % to 40.0 wt. %, preferably from 0.1 wt. % to 30.0 wt. %, preferably from 0.1 wt. % to 25.0 wt. %, preferably from 1.0 wt. % to 10.0 wt. %, preferably from 1.0 wt. % to 6.0 wt. %, preferably from 2.0 to 5.0 wt. %, based on the total weight of the sizing composition.

The dispersion medium may be present in an amount from 60.0 wt. % to 99.99 wt. %, preferably from 70.0 wt. % to 99.9 wt. %, preferably from 75.0 wt. % to 99.9 wt. %, preferably from 90.0 wt. % to 99.0 wt. %, preferably from 94.0 wt. % to 99.0 wt. %, preferably from 95.0 to 98.0 wt. %, based on the total weight of the sizing composition.

It is preferred that prior to sizing the reinforcing fiber, the sizing composition is further diluted with dispersion medium in order to provide the desired sizing content on the reinforcing fiber. Preferably, the sizing agent is present in an amount from 1.0 wt. % to 6.0 wt. %, preferably from 1.0 wt. % to 5.0 wt. % and the dispersion medium is present in an amount from 94.0 wt. % to 99.0 wt. %, preferably in an amount from 95.0 wt. % to 99.0 wt. %, based on the total weight of the sizing composition.

The sizing composition may be in the form of solution, dispersion, or emulsion in a solvent. Preferably, the sizing composition is in the form of an emulsion with the functionalized polyolefin polymer being emulsified at a temperature higher than the melting point of the functionalized polyolefin polymer and stabilized with a suitable combination of ionic and non-ionic surfactant. The inventors surprisingly found that the desired emulsion stability is achieved even when an alkali metal based ionic surfactant was used to formulate the sizing agent.

Preparing the Sizing Composition

The sizing composition may be prepared by introducing the sizing agent in accordance with the invention, in a reactor vessel, containing a suitable dispersion medium, for example water. Thereafter, the reactor may be purged with an inert gas, for example nitrogen and thereafter the reaction mixture may be stirred or agitated at around 700-950 rpm and at any temperature between 150° C. to 175° C. After the completion of about one or two hours, the reactor vessel may be cooled for about an hour and thereafter the sizing composition may be recovered from the reactor vessel.

It is preferred that when the sizing composition is a water based emulsion, each of the components constituting the sizing agent may be beaded to water with agitation followed by heat treatment. The step of agitation may be carried in a homogenizer, mixer, or ball milled with mechanical shear, and emulsified through phase conversion by gradually adding water.

Sized Reinforcing Fiber

In some aspects of the invention, the invention is directed to a sized reinforcing fiber. The sized reinforcing fiber may comprise a reinforcing fiber selected from the group consisting of carbon fiber, basalt fiber, glass fiber, polymer fiber, and metal fiber, and wherein at least a portion of the reinforcing fiber is provided with the sizing agent in accordance with the present invention. The expression “at least portion” means at least 50%, preferably at least 60%, preferably at least 90%, preferably at least 100%, of the external surface of the reinforcing fiber.

Preferably, the reinforcing fiber is carbon fiber. The carbon fiber may include graphite, expanded graphite, graphene, a pyrolyzed carbon fiber, a carbon nanotube, graphitized carbon black, and combinations thereof. The carbon fibers may be in the form of a tow, knitted or braided form or in the form of a mat that is woven or nonwoven. The fibers can be continuous or chopped. The dimensions of the fibers may be in the form of chopped fiber cut into 1 to 15 mm long for manufacturing fiber-reinforced composites.

It is preferred that at least a portion of the reinforcing fiber is coated or sized with the sizing agent in accordance with the present invention. Preferably, the entire surface of the reinforcing fiber is coated or sized with the sizing agent in accordance with the present invention. The sizing agent may be present in an amount from 0.01 wt. % to 3.0 wt. %, preferably from 0.05 wt. % to 1.5 wt. %, preferably from 0.1 to 1.2 wt. % based on the weight of the sized reinforcing fibers.

As evidenced from the experimental results provided in this disclosure, when the reinforcing fiber is sized with the sizing agent of the present invention, the reinforcing fiber is able to retain or even improve on its tensile properties. This is particularly advantageous, as the sized fibers can be used for preparing the polymer composite having the desired mechanical properties.

Process for Preparing the Sized Reinforcing Fiber

In an aspect of the invention, the invention relates to a process for producing the sized reinforcing fiber in accordance the invention. The process for producing the sized reinforcing fiber may comprise the steps of:

• • providing the reinforcing fiber in accordance with the invention, preferably wherein the reinforcing fiber is carbon fiber;
  • contacting the reinforcing fiber with the sizing composition in accordance with the invention and obtaining a precursor sized reinforcing fiber; and
  • drying the precursor sized reinforcing fiber to obtain the sized reinforcing fiber.

The step of contacting the reinforcing fiber may involve any one of spraying the reinforcing fibers with the sizing composition or impregnating the reinforcing fibers in the sizing composition, or immersing the reinforcing fibers in a sizing bath comprising the sizing composition.

In some aspects of the invention, the step of “contacting the reinforcing fiber with the sizing composition” involves the step of drawing the reinforcing fiber through a sizing bath containing the sizing composition and thereafter forming the sized reinforcing fiber. The drawing of the reinforcing fibers may involve drawing the reinforcing fibers through the sizing bath using rollers. The drawing of the reinforcing fibers with rollers, is particularly preferred, as it allows uniform application of the sizing on the reinforcing fibers.

Preferably, the process for applying the sizing composition may involve the steps of pulling the reinforcing fiber from a creel by a downstream winder, passing the reinforcing fiber through the sizing bath to size the fiber and then subsequently through a dryer such as a heated tube, having one or more temperature-controlled zones, and subsequently winding the sized reinforcing fiber onto a spool. The drying step may be carried out by heating at a suitable temperature and for a suitable time period sufficient to remove any water or any traces of solvent (the dispersion medium).

The process of drying may involve passing the precursor sized reinforcing fiber through one or more heating zones operated at any temperatures from about 50° C. to about 90° C. and for a time period of about 0.5 to 2.0 minutes. Alternatively, the drying step may be carried out by drying the precursor sized reinforcing fiber under ambient room temperature (˜19° C.-32° C.) over a time period ranging from about 20 hours to 72 hours.

Polymer Composite

In an aspect of the invention, the invention relates to a polymer composite comprising:

• • a polymer matrix comprising a polyolefin polymer, preferably the polyolefin polymer is selected from polypropylene or polyethylene, more preferably the polyolefin polymer is polypropylene; and
  • one or more sized reinforcing fiber in accordance with the present invention, wherein the one or more sized reinforcing fiber is dispersed in the polymer matrix. Preferably, the one or more sized reinforcing fiber is a sized carbon fiber.

Preferably, the polymer composite is a carbon fiber reinforced polypropylene. The polypropylene may comprise a polypropylene homopolymer, preferably an iso-tactic polypropylene (iPP). Alternatively, the polypropylene may be a propylene-ethylene random copolymer (random PP) or a heterophasic polypropylene. The polyethylene may be a copolymer derived from ethylene and one or more alpha olefin having 4 to 10 carbon atoms, preferably an alpha-olefin having 6 or 8 carbon atoms.

The inventors surprisingly found that when the sized reinforcing fiber is dispersed in the polymer matrix, the sized reinforcing fiber is able to demonstrate desired adhesion with the polymer matrix. A suitable indicator for determining the extent of adhesion between the sized reinforcing fiber and the polymer matrix is by measuring the apparent interfacial shear strength between the sized fiber and the polymer matrix.

Accordingly, higher the apparent interfacial shear strength, higher would be the extent of adhesion or compatibility between the sized reinforcing fiber and the polymer matrix. One of the tests for determining the apparent interfacial shear strength is the Micromechanical Single-Fibre Pull-Out Test in accordance with DIN SPEC 19289.

The polymer composite may be manufactured by any known process of preparing polymer composites such as melt compounding or solution processing. Under solution processing, the reinforcing fibers may be impregnated with a solution comprising a polymer, and the solvent may be subsequently removed. The solution may be selected to be suitable for dissolving the polymer, but not the sizing agent.

Alternatively, when the manufacturing method involves melt compounding, the polymer, is blended with the reinforcing fibers in a high speed mixer or by hand mixing. The blend may thereafter be fed into the throat of an extruder via a hopper. Alternatively, the reinforcing fibers may be incorporated into the polymer by feeding it directly into the extruder at the throat and/or downstream through a side stuffer, or by being compounded into a masterbatch with a desired polymer and fed into the extruder. The composition may thereafter be extruded to provide an extrudate with a desired shape. Alternatively, the extrudate may be immediately quenched in a water bath and pelletized. Such pellets may be used for subsequent molding, shaping, for various industrial application.

In an aspect of the invention, the invention relates to articles molded from the polymer composite in accordance with the present invention. The articles may be automobile components, battery casing and tray, consumer goods, electronic and medical devices.

The present invention will now be further elucidated based on the following non-limiting examples.

Examples

Material: For the purposes of the examples the following materials were used:

TABLE 1
Component/
Material	Description/Grade
Reinforcing Fiber	Carbon Fiber from SGL Carbon
Dispersing Medium	De-ionized water
Polymer Matrix	Polypropylene
	SABIC ® PP595A (Melt Flow Rate of 47 dg/min
	at 230° C. and 2.16 kg determined in accordance
	with ISO 1133).
Inorganic Base	Potassium Hydroxide pellets (purity at 85%,
	CAS# 1310-58-3)
Organic Base	N,N-dimethyl ethanol amine (CAS# 108-01-0)
	(DMAE)
Functionalized	Maleic anhydride grafted polypropylene
Polyolefin polymer	(MA-g-PP) CAS# 25722-45-6 (Sigma-Aldrich).
	Acid number ~74.6.
	Maleic Anhydride content of 7.7 wt. %
Non-ionic surfactant	polyoxyethylene (9) nonylphenylether branched -
	IGEPAL CO-630 CAS# 68412-54-4(Sigma-
	Aldrich). Initial Boiling Point ~250° C.
	Density 1.056 g/ml at 25° C.
Ionic surfactant	AEROSOL OT 70 PG: CAS# 78207-03-1 (Cytec).
	Sodium 1,4-bis[(2-ethylhexyl)oxy]-1,4-
	dioxo-2-butanesulfonate
Compound A	Sodium metabisulfite (CAS#7681-57-4)
Benchmark sizing	Hydrosize ® Carbon 110 from Michelman
agent (BSA)

Testing protocols: The following test protocols and standard were followed:

TABLE 2
Test Protocols	Description/Grade
Sized Carbon fiber	The tensile strength and tensile modulus was
Tensile Strength	determined in accordance with ISO 11566: 1996.
and Tensile Modulus	In particular a Textechno FAVIMAT +
	(Textechno) instrument was used with a force
	cell of 610 cN and a gauge length calibration
	of 50 mm.
Apparent Interfacial	The Apparent Interfacial Shear Strength was
Shear Strength (ILSS)	determined in accordance with DIN SPEC 19289.

Three sizing agent samples (IE1-IE3) in accordance with the invention, were formulated and the corresponding sizing compositions were prepared. Thereafter, the sizing compositions were used for preparing the sized carbon fibers. The performance of the sizing agents (IE1-IE3) were evaluated against the Benchmark Sizing Agent (BSA) and also against unsized carbon fibers.

The following sizing agent samples were formulated:

	TABLE 3
	IE1	IE2	IE3

	Functionalized	67.9%	72.7%	65.6%
	Polyolefin polymer
	(wt. %)
	Inorganic Base (wt. %)	12.2%	6.2%	0.0
	Organic Base (wt. %)	0.0	0.0	15.4%
	Non-ionic surfactant	17.7%	18.9%	17.1%
	(wt. %)
	Ionic surfactant (wt. %)	1.5%	1.5%	1.3%
	Compound A (wt. %)	0.7%	0.7%	0.6%
	Total weight (g)	44.12 g	41.22 g	45.72 g
		(100%)	(100%)	(100%)

Preparing the Sizing Composition

The sizing composition were prepared by adding the sizing agents to a de-ionized water followed by mixing and emulsification. The concentration of the sizing agent in the resultant sizing compositions is provided under Table 4. In particular, the process followed the step of introducing the sizing agent comprising the functionalized polyolefin polymer (maleic anhydride grafted polyolefin), the base compound, the non-ionic surfactant (polyoxyethylene (9) nonylphenylether branched), the ionic surfactant (AEROSOL OT 70 PG) and the compound A (sodium metabisulfite) to a reactor vessel containing deionized water and thereafter the reactor was purged with nitrogen and a mixture was obtained. The mixture was thereafter stirred at 850 rpm at a temperature of 175° C. After completion of heating for about one hour at 175° C., the reactor was cooled and the sizing composition was recovered. This process was followed for each of the sizing agents (IE1-IE3) and the Benchmark Sizing Agent (BSA) to obtain the sizing composition. Each of the sizing compositions were in the form of emulsified aqueous dispersions.

For each of the sizing compositions, the pH of the sizing composition was determined using a pH meter at room temperature. It is observed from Table 4, that the commercial benchmark sizing agent (BSA) was acidic in nature while the sizing composition IE2 and IE3 were basic in nature. The sizing composition IE1 had a pH of nearly 12 indicating the strong basic nature of the sizing composition.

	TABLE 4
	Benchmark
	sizing
	composition	IE1	IE2	IE3

Concentration	35.0	wt %	40.0	wt %	33.3	wt %	39.6	wt %
of the sizing
agent in the
sizing
composition
(wt. %)
After dilution	3.8	wt. %	3.1	wt. %	3.5	wt. %	3.5	wt. %
concentration
of the sizing
agent in the
sizing
composition
(wt. %)

pH	6.7	~12.0	~7.2	~8.5

Preparing the Sized Carbon Fiber

The sizing agent so obtained from each of the sizing agents IE1-IE3 was further diluted with de-ionized water and was used for sizing a bundle of unsized carbon fiber. The concentration of the sizing agent before and after dilution diluted in the sizing composition is provided in Table 4. The process for preparing the sized carbon fiber involved the step of drawing the unsized carbon fiber bundle through a sizing bath containing the sizing compositions that were prepared. The unsized carbon fiber bundle may be drawn by using a tension of 1.0 to 1.2 bar at a speed between 0.8 to 1.0 meter/minute.

Excess sizing agents were squeezed off with the aid of counter-rotating rollers. The coated carbon fibers were dried in a circulating air drying oven at 120° C. for 3 h to finally prepare the samples for further evaluation. The sizing content on the resultant sized carbon fibers for each of the sized carbon fibers obtained was approximately 1.0-1.1 wt. % based on the total weight of the sized carbon fiber.

The resultant sized carbon fibers were thereafter evaluated for its mechanical properties as provided below using the single fiber tensile measurement:

	TABLE 5
	Tensile	Tensile
	Strength (MPa)	Modulus (GPa)

	Unsized carbon fiber	~3227	~270
	Carbon fiber sized with	~3334	~260
	Benchmark sizing agent
	Carbon fiber sized with	~3393	~271
	sizing agent (IE1)
	Carbon fiber sized with	~3496	~272
	sizing agent (IE2)
	Carbon fiber sized with	~3520	~266
	sizing agent (IE3)

Micro-mechanical Single fiber pullout test: The extent of compatibility between the sized carbon fibers and the polypropylene matrix was determined using apparent interfacial shear strength measurements using the single fiber pullout test. The sized carbon fibers that were prepared, were used to evaluate the interfacial shear strength by following the method as described in DIN SPEC 19289. Four different samples were prepared using the sized carbon fibers obtained from each of IE1-IE3 sizing agents and the Benchmark Sizing Agent.

Samples were prepared by embedding each of the sized carbon fiber in a melt polypropylene matrix (SABIC® PP595A). A sample holder containing the polymer matrix was transferred to an embedding device. A single fiber of 1 mm length was embedded into a molten polypropylene polymer matrix by a computer controlled procedure. Embedding procedure was assisted by a two-camera-system to enable the placement and the observation of the fiber into the molten polymer matrix. The fiber was embedded at a constant velocity.

The real embedded length was measured after the pull-out test on an optical microscope. Subsequently, the pull-out test was performed under quasi-static loading conditions (QSFPO) at a pull-out velocity of 0.001 mm/s and under dynamic loading (DSFPO) at 10 mm/s, respectively. During the test, the force-displacement curve was recorded in the case of QSFPO. At least 15 specimens for each fiber type were tested to ensure meaningful statistical evaluation. From the force-displacement curve the apparent interfacial shear strength was determined.

The results are provide in the table below:

TABLE 6
	Apparent Interfacial Shear
Sample	Strength (N/mm2)

Polypropylene composite with	4.2
unsized carbon fiber
Polypropylene composite with sized	8.0
carbon fiber with Benchmark sizing
agent (BSA)
Polypropylene composite with sized	7.6
carbon fiber with sizing agent (IE1)
Polypropylene composite with sized	8.0
carbon fiber with sizing agent (IE2)
Polypropylene composite with sized	10.0
carbon fiber with sizing agent (IE3)

Results and Conclusion: For the sizing composition prepared from the sizing agents IE1-IE3, no gel formation was observed even after 30 days, indicating that the sizing composition had the desired emulsion stability.

From the data provided under Table 5, the present inventors concluded that the mechanical properties of the sized carbon fibers prepared from the sizing agents IE1-IE3 was retained and in some instance even further improved upon, in comparison to the unsized carbon fiber. For example, in all the instances, the sized carbon fibers prepared from the sizing agents (IE1-IE3), had higher tensile strength than the initial unsized carbon fiber.

Further, from Table 5 the present inventors concluded that the sized carbon fibers prepared from the sizing agents IE1-IE3, have a higher tensile strength than the sized carbon fiber prepared from the commercially procured Benchmark Sizing Agent (BSA).

From the data provided under Table 6, the present inventors concluded that the sized carbon fibers prepared from sizing agents IE2 and IE3 demonstrate high fiber-matrix adhesion indicating excellent compatibility between the fiber and the polymer matrix.

In fact the polypropylene composite prepared from sized carbon fiber having IE3 as the sizing agent, has a higher adhesion to the polypropylene matrix than even the carbon fibers sized with the Benchmark Sizing Agent (BSA). The carbon fiber prepared from sizing agent IE2 had similar levels of adhesion or compatibility to the polypropylene matrix as that of the carbon fiber sized with the Benchmark Sizing Agent (BSA). From the results provided under Table 6 the inventors concluded that a suitable selection of the sizing agent and the corresponding sizing composition influences the property of the sized carbon fibers in terms of compatibility with the polymer matrix.

Further, from the single fiber pullout test it was observed that there was no fiber breakage or fuzz formation indicating that the sizing agents IE1-IE3 imparted the desired protective coating on the carbon fiber surface.