WO2014088515A1

WO2014088515A1 - A polymer composite comprising functionalised silica particles

Info

Publication number: WO2014088515A1
Application number: PCT/SG2013/000514
Authority: WO
Inventors: Nopphawan Phonthammachai; Chaobin He; Chee Chuan YEO
Original assignee: Agency For Science, Technology And Research
Priority date: 2012-12-04
Filing date: 2013-12-04
Publication date: 2014-06-12

Abstract

There is provided a polymer composite comprising a plurality of surface functionalized silica particles dispersed in a polymer matrix, wherein the surface functionalized silica particles are at least partially coated with a resin carrier.

Description

A polymer composite comprising functionalised silica particles

Technical Field

The present invention generally relates to a polymer composite such -as a polymer nanocomposite . The present invention also relates to a method for forming a polymer composite such as a polymer nanocomposite as well as a filler ^' for a polymer composite such as a polymer nanocomposite.

Background

Silica has been proven as a nano- filler to enhance the thermal and mechanical properties of thermoplastic polymers. However, the dispersion of silica nanoparticles and its compatibility with the thermoplastic polymer are major concerns for the manufacturing of such polymer nanocomposites . Many technologies have been developed to improve the silica- thermoplastic polymer compatibility and reduce the aggregationof silica nanoparticles in the thermoplastic polymer. A known method involves the synthesis of silica nanoparticles by solution blending process to form dispersed silica in solvent. The silica surface is then f nctionalized using a silane coupling agent to form organo-silane functionalized silica that can be linked with grafting polymer. Following which, the organo-silane functionalized silica surfaces is grafted by a polymer under severe conditions such as high pressure or inert gas at elevated temperatures (80 to 140°C) for long reaction periods (6 to.36 hours) and in the presence of poisonous organic solvents (such as xylene, toluene, benzene, methyl isobutyl ketone) . The polymer grafted^' silica nanoparticles are finally compounded with the thermoplastic polymer in melt state using an extruder or mixer. The resulted polymer nanocomposites show dispersed silica with smaller aggregated size than non-grafted silica, with a reduction from the micron- size to the nano- size (150 to 400 rati) . In another method, the dispersion of silica in thermoplastic polymer is done by dispersing colloidal silica in dissolved thermoplastic polymer and drying at an elevated temperature to form polymer nanocomposite . The dispersion of silica in thermoplastic polymer may be further improved by this process. However, this method is not adaptable for large-scale manufacturing due to the large amount of organic solvent ^'required to dissolve the thermoplastic polymer. Hence, the process to remove,, recycle and dispose of huge volumes of solvent is costly.

It can clearly be seen from the above methods that complex processes under severe synthesis conditions (high temperature, pressure, chemicals) at long reaction periods are required in the preparation of polymer nanocomposites . The manufacturing cost and reaction time to produce polymer nanocomposite are, thus, far increased from neat thermoplastic polymer.

There . is a. need to provide a method to form a polymer nanocomposite that overcomes, or at least ameliorates, one or more of the disadvantages described above.

There is a need to provide a polymer nanocomposite with enhanced properties as compared to those formed according to the methods mentioned above .

Summary

According to a first aspect, there is provided a polymer composite comprising a plurality of surface functionalized silica particles dispersed in a polymeric material, wherein the surface unctionalized silica particles are at least partially coated with a resin carrier.

The polymer composite may be a polymer nanocomposite. The surface functionalized silica particles coated with a resin carrier may be in the nano-size range.

Advantageously, the polymer composite or nanocomposite may have better properties as compared to another polymer composite or nanocomposite having non- coated, non- functionalized silica particles or nanoparticles . The polymer composite or nanocomposite may have at least one improvement such as better mechanical properties, higher thermal stability, improved flexural modulus, improved tensile modulus, higher degradation temperature and/or higher glass transition temperature.

According to a second aspect, there is provided a method for forming a polymer composite as defined above comprising the step of compounding a plurality of polymerizable resin coated surface functionalized silica particles with a polymeric material.

During the compounding step, the polymerizable resin may polymerize or react with the surface functional groups on the silica particle and may also polymerize or react with the polymeric material. Hence, the polymerizable resin may polymerize during the compounding step to form a resin carrier that coats the surface functionalized silica particles in the resultant polymer composite.

The method may comprise, before the compounding step, the step of manufacturing the polymerizable resin coated surface functionalized silica particles. The manufacturing step may comprise the step of mixing a substantially homogeneous mixture of silica precursors, a polymerizable resin, a coupling agent having functional groups and an alkaline catalyst under conditions to produce polymerizable resin coated surface functionalized silica particles. Following which, the method may comprise the step of reducing the particle size of the polymerizable resin coated surface functionalized silica particles.

Advantageously, the manufacturing step may be considered as an in situ single step (that is, an "one- pot" manufacturing step) to form the polymerizable resin coated surface functionalized silica particles. The manufacturing step may be undertaken in a single reaction zone .

The manufacturing step may not require additional steps such as additional silica modification steps or coating of polymer on silica surfaces.

Advantageously, the presence of the. alkaline catalyst in the homogeneous mixture may aid in forming and functionalizing the silica particles in one step.

According to a third aspect, there is provided use of surface functionalized silica particles coated with a , resin carrier as a filler in a polymer composite.

Advantageously, the use of such silica particles or nanoparticles as filler may increase or enhance one or more properties of .the polymer composite or polymer nanocomposite as mentioned above.

Definitions

The following words and terms used herein shall have the meaning indicated:

The term "polymer composite" is used herein, is to be interpreted broadly to mean a polymer, copolymer or polymer blend having particles or fillers dispersed within the polymeric material. The particles or fillers may be wholly and/or partially encapsulated or dispersed within the polymeric material . Where these particles or fillers are in the nano-size range, for example, having average particle sizes of less than 1000 nm, or . less than 500 nm, or less than 100 nm, the resultant polymer composite may be termed as a "polymer. nanocomposite" .

The term "silica nanoparticles", as used herein, is to be interpreted broadly to refer to silica nanoparticles that have an average particle size of less than about 1000 nm, less than about 500 nm, or less than about 100 nm. When determining the particle size, this may be based on the maximum dimension of the silica nanoparticles. Hence, where the silica nanoparticles have a generally elongate shape, the maximum dimension refers to the length dimension of ^" the nanoparticles. The silica nanoparticles also refer to a plurality of discrete nanoparticles of oxide of silicon having the approximate chemical formula Si0₂, without regard to shape, morphology, porosity, and water or- hydroxy1 content. The silica nanoparticles may be at least partially coated or completely coated by the resin _. carrier. The silica nanoparticles may be individually coated by the resin carrier such that each.silica nanoparticle can be considered as not substantially agglomerating or clumping together with other nanoparticles. Hence, the silica nanoparticles may be considered as being "monodispersed" within^' the polymerizable resin coating.

The term "substantially homogeneous mixture" as used herein, is to be interpreted broadly to refer to a mixture approaching uniform composition throughout.

' The term "surface aminated" when referring to silica

(nano) particles , is to be interpreted broadly to refer to any . silica (nano) particles having coupled to its surface, at least . one group chosen from primary amines , secondary amines, tertiary amines, and quaternary ammonium groups.

The term "filler" as used herein, is to be interpreted broadly to refer to additives which increase the volume and/or the weight of a polymeric material, and which are able to alter the physical properties of the resultant polymeric material. The term "filler" may be used to refer to, or be used interchangeably with the phrase . "resin coated surface functionalized silica (nano) particles" . The "filler" may also be "monodispersed" within the polymeric material forming the polymer (nano) composite . The word "substantially" does not exclude "completely" e.g. a composition which is "substantially free" from Y may be completely free from Y. Where necessary, the word "substantially" may be omitted from the definition of the invention.

Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended' to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

As used herein, the term "about", in the context of concentrations. of components of the formulations, typically means +/- 5% of the stated value, more typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more typically, +/- 2% of the stated value, even more typically .+/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range -format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3 , from 1 to , ■from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6· etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range .

Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the ■ generic description of the embodiments with a proviso or negative limitation, removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

Detailed Disclosure of Embodiments

Exemplary, non- limiting embodiments of a polymer composite will now be disclosed. The polymer composite comprises a plurality of surface functionalized silica particles dispersed in a polymer matrix, wherein the surface functionalized silica particles are at least partially coated with a resin carrier.

The polymer composite may be a polymer nanocomposite .

The silica particles may be silica nanoparticles.

The functional groups on the surface of the silica particles or nanoparticles may be amine functional groups. The amine functional groups may be selected from primary amines, secondary amines, tertiary amines or quaternary amines. The silica particles or nanoparticles may then be considered as being surface aminated or amine functionalized silica particles or nanoparticles . By having functional groups on the surface of the silica particles or nanoparticles, this may aid in promoting dispersion of the silica particles or nanoparticles in the polymeric material making up the polymer composite or nanocomposite. In addition, the surface functional groups may aid in improving the bonding force between the silica particles or nanoparticles and the polymerizable resin.

The functional groups may be introduced onto the surface of the silica particles or nanoparticles by a coupling agent. The^' coupling agent may be an organosilane compound that has undergone hydrolysis . Hence, the hydrolyzed organosilane compound may have a hydroxy1 functional group to participate in a condensation reaction with hydrolyzed silica particles or nanoparticles to form surface-functionalized silica particles nanoparticles and another functional group that can react with the polymerizable resin. For example, the functional group that can react with the polymerizable resin may be an amine group. Hence, the hydrolyzed organosilane compound may comprise an amine group. In another embodiment, the functional group that can react with the matrix may be an epoxide group. Hence, the hydrolyzed organosilane compound may comprise an epoxide group .

The hydrolyzed organosilane coupling agent may be derived from an organosilane coupling agent having the above functional group that can react with the polymerizable resin as well as a functional group that can undergo hydrolysis to form the hydroxyl functional group. The functional group that can undergo hydrolysis may be an alkoxy functional group. Hence, the organo-silane coupling agent may have amine functional groups and alkoxy functional groups .

The organo-silane coupling agent may be selected from the group consisting of epoxysilane, mercaptosilane, alkylsilane, phenylsilane, ureidosilane and vinylsilane, titanium based compounds^", aluminum chelates, and aluminum/zirconium based compounds.

Exemplary organo-silane coupling agents include silane coupling agents such as β-(3,4- epoxycyclohexyl) ethyltrimethoxysilane, γ- glycidoxypropyltrimethoxysilane , 3- glycidoxypropylmethyldimethoxysilane, γ- mercaptopropyltrimethoxysilane ,

aminopropyltrimethoxysilane , γ- aminopropylmethyldimethoxysilane, γ- aminoprppyltriethoxysilane, Y- aminopropylmethyldiethoxysilane, Y- ^■ (N, N- dimethyl) aminopropyltrimethoxysilane, Y- ^■ (N, N- diethyl) aminopropyltrimethoxysilane, Y- ^■ (N, N- dibutyl) aminopropyltrimethoxysilane, Y- (N- methyl ) anilinopropyltrimethoxysilane, Y- (N- ethyl) anilinopropyltrimethoxysilane, Y- ^• (N, N- dimethyl) aminopropyltriethoxysilane, Y- ^• (N,N- diethyl ) aminopropyltriethoxysilane , Y- ^• (N, N- dibutyl ) aminopropyltriethoxysilane , Y- (N- methyl ) aminopropyltriethoxysilane, Y- (N- ethyl ) aminopropyltriethoxysilane , Y- ^■ (N, N- dimethyl ) aminopropylrnethyldimethoxysilane, Y- ^• (N, N- diethyl) aminopropylmethyldimethoxysilane, Y- - (N, N- dibutyl) aminopropylmethyldimethoxysilane, Y- (N- methyl ) aminopropyl ethyldimethoxysilane, Y- (N- ethyl) amiopropylmethyldimethoxysilane , N-

(trimethoxysilylpropyl) ethylenediamine, N-

(dimethoxymethylsilylisopropyl ) ethylenediamine, Y- mercaptopropylmethyldimethoxysilane titanate coupling agents such as isopropyltri (N-aminoethyl- aminoethyl) titanate . These may be used alone or in combination of two or more thereof .

In one embodiment, the organo-silane coupling agent is an organosilane compound having the formula (Y-R)_nSiX_m, where Y is a chemical moiety capable of chemically reacting with the functional group of the matrix, R is a C_3-6-alkyl group, X is a C_1-e-alkoxy group, and n and m are integers such that the sum of n and m is 4 (n+m=4) . Y may be an amine group. Accordingly, the coupling agent may be aminopropyltrimethoxysilane (APTMS) having the formula (I) below:

5

(I)

In another embodiment, the organosilane coupling agent may be 3 -glycidoxypropyltrimethoxysilane .

The polymerizable resin may polymerize during a compounding step to form a resin carrier. During the compounding step, the polymerizable resin may polymerize or react with the surface functional groups on the silica particle or nanoparticle and may also polymerize or react with the polymeric material. Hence, .the- polymerizable resin may polymerize during the compounding step to form a resin carrier that coats the surface functionalized silica particles or nanoparticles in the resultant polymer composite or nanocomposite . The polymerizable resin or resultant resin carrier may have two purposes. Firstly, the polymerizable resin or resin carrier may make the silica particle or nanoparticle more compatible with the polymeric material by making the silica surfaces more hydrophobic. Secondly, the polymerizable resin or resin carrier may react with the silica and the polymeric material.. Due to the smaller molecules of the resin carrier, they, can link up with the bigger molecules of the silica (nano) articles or polymeric material, or both) . The inclusion of the smaller molecules may reduce the Tg and mechanical property of the final polymer composite or nanocomposite.

The polymerizable resin or resin carrier may comprise a thermosetting polymer. The thermosetting polymer may comprise an epoxy matrix material . The epoxy matrix material may comprise an epoxy-containing monomer, oligomer, polymer or combinations thereof.

The epoxy matrix material may be of the bisphenol A type epoxy resin, bisphenol S type epoxy resin, bisphenol K type epoxy resin, bisphenol F type epoxy resin, phenolic novolak type epoxy resin, cresol novolak type epoxy resin, alicyclic epoxy resin, heterocyclic epoxy resins (such as triglycidyl isocyanuric and hydantoin epoxy) , hydrogenated bisphenol A type epoxy resin and aliphatic epoxy resins (such as propylene glycol -diglycidyl ether and pentaerythritolpolyglycidyl ether) .

The epoxy matrix material may also be obtained by the reaction between an aromatic, aliphatic or alicyclic carboxylic acid and epichlorohydrin. The epoxy matrix material may have a spiro ring, a glycidyl ether type epoxy resin which is obtained by the reaction between ortho-allyl phenolic novolak compound and epichlorohydrin. The epoxy matrix .material may be of a glycidyl ether type epoxy resin which is obtained by the reaction between diallyl bisphenol compound having, an allyl group in the ortho site of bisphenol A with respect to the hydroxyl group and epichlorohydrin. The epoxy matrix material may be obtained by the reaction between a phenol and an epichlorohydrin in which the reactants may be bisphenols (such as ' bisphenol A and bisphenol F) , resorcinol, dihydroxynaphthalene, trihydroxynaphthalene, dihydroxybiphenylfluorene , trishydroxylmethane , tetrakishydroxphenlylethane , novolaks, condensates of dicyclopentadiene and phenols. The epoxy matrix material may be obtained by ^"the reaction between amines and epichlorohydrin in which the reactants may be tetraglycidyldiaminodiphenylmethane , aminophenol , aminocresol and xylenediamine.. In addition, derivatives such as ethylene oxide, propylene oxide, styrene oxide, cyclohexene oxide and phenyl glycidyl ether may be used as desired. These epoxy matrix materials can be used singly or in the form of a mixture of at least two kinds of the epoxy resins.

In one embodiment, the polymerizable resin or resin carrier may be an aliphatic, cycloaliphatic or aromatic epoxy resin which has a plurality of epoxide groups . The epoxy resin may have two epoxide groups such as diglycidyl ether of bisphenol A (DER™ _.332, by Dow), represented by formula (II) .

(ID .

The polymeric material may comprise a thermoplastic polymer. The thermoplastic polymer may comprise monomers selected from the group consisting of acrylates, phthalamides, acrylonitriles , cellulosics, styrenes, . alkyIs,. alkyls methacrylates , alkenes, halogenated alkenes, amides, imides, aryletherketones , butadienes, ketones, esters, acetals, acetates, sulfones, polyols, isocyanates, carbonates and combinations, thereof.

Exemplary monomers to form the thermoplastic polymer may be selected from the group consisting of methyls, ethylenes, propylenes, methyl methacrylates, methylpentenes , vinylidene, vinylidene chloride, etherimides, ethylenechlorinates , urethanes, ethylene vinyl alcohols, fluoroplastics , carbonates, acrylonitrile- butadiene- styrenes , etheretherketones , ionomers, butylenes , phenylene oxides , sulphones , ethersulphones , phenylene sulphides, elastomers, ethylene terephthalate , naphthalene terephthalate, ethylene naphthalene and combinations thereof . The thermoplastic polymer may be selected from the group consisting of polypropylene, polyethylene, polystyrene, polyamide, polybutylene, poly (vinyl chloride) , ethylene vinyl acetate, . polyethylene terephthalate, polysulfone, polyurethane and combinations thereof.

In the polymer nanocomposite, the average particle size of the silica nanoparticles coated by the resin carrier may be less than about 1000 nm. The average particle size may be in the range of about 10 nm to about 500 nm, about 50 nm to about 500 nm, about 100 nm to about 500 nm, about 150 nm to about 500 nm, about 200 nm to about 500 nm, about 250 nm to about 500 nm, about 300 nm to about 500 nm, about 350 nm to about 500 nm, about 400 nm to about 500 nm, about 450 nm to about 500 nm, about 10 nm to about 50 nm, about 10 nm to about 100 nm, about 10 nm to about 150 nm, about 10 nm to about 200 nm, about 10 nm to about 250 nm, about 10 nm to about 300 nm, about 10 nm to about 350 nm, about 10 nm to about 400 nm and about 10 nm to about 450 nm. In one embodiment, the average particle size of the resin coated surface functionalized silica nanoparticles may be less than about 1000 nm, or about 10 nm to about 500 nm.

The resin coated surface functionalized silica particles nanoparticles may be present in the polymer composite or . nanocomposite at a weight% in the range of about 0.1 to about 30 wt%, based on the weight of the polymeric material . ¹ The weight% may be in the range of about 0.1 to about 1 wt%, about 0.1 to about 5 wt%, about 0.1 to about 10 wt%, about 0.1 to about 15 wt%, about 0.1 to about 20 wt%, about 0.1 to about 25 wt%, about 1 to about 30 wt%, about 5 to about 30 wt%, about 10 to about 30 wt%, about 15 to about 30 wt%, about 20 to about 30 wt% and about 25 to about 30 wt%. Exemplary, non-limiting embodiments of a method for forming a polymer composite or nanocomposite will now be disclosed. The method comprises the step of compounding a plurality of polymerizable resin coated surface · functional!zed silica particles or nanoparticles with a polymeric material.

The compounding step may be undertaken at a compounding temperature in the range of about 150°C to about 200°C, about 150°C to about 160°C, about 150°C to about 170°C, about 150°C to about 180°C, about 150°C to about 190°C, about 160°C to about 200°C, about 170°C to about 200°C, about 180°C to about 200°C and about 190°C to about 200°C. The compounding temperature may be about 180°C,

The compounding step may be undertaken for a period of compounding time in the range , of about 5 minutes to about 30 minutes, about 5 minutes to about 10 minutes, about 5 minutes to about 15 minutes, about 5 minutes to about 20 minutes, about 5 minutes to about 25 minutes, about 10 minutes to about 30 minutes, about 15 minutes to about 30 minutes, about 20 minutes to about 30 minutes and about 25 minutes to about 30 minutes. The compounding time may be about 15 minutes .

The compounding step may be carried out using a machine selected, from the group consisting of an extruder, a mixer and combinations thereof in a sequential manner. The compounding machine may be obtained Brabender^®.

As mentioned above, during the compounding step, the polymerizable resin may polymerize or react with the surface functional groups on the silica particles or nanoparticles and may also polymerize or react with the polymeric material. Hence, the polymerizable resin may polymerize during the compounding step to form a resin carrier that coats the surface functionalized silica particles or nanoparticles in the resultant polymer composite or nanocomposite .

The method may comprise, before the compounding step, the step of manufacturing the polymerizable resin coated surface functionalized silica particles or nanoparticles .

The manufacturing step may comprise the step of mixing a substantially homogeneous mixture of silica precursors, a polymerizable resin, a coupling agent having functional groups and an alkaline catalyst under conditions to produce polymerizable resin coated surface functionalized silica particles or nanoparticles. If necessary, an additional step may be carried out in order to reduce the particle size of the polymerizable resin coated surface functionalized silica particles or nanoparticles to the nano-size or to even reduce the size further from a bigger nanoparticle to a smaller nanoparticle. Hence, the method may also comprise the step of reducing the particle size of the polymerizable resin coated surface. functionalized silica particles or nanoparticles. The reducing step may comprise the step of grinding the polymerizable resin coated surface functionalized silica particles or nanoparticles. The grinding step may be undertaken using mechanical grinding processes such as hand grinding with mortar, ball milling, or freeze grinding.

The coupling agent and polymerizable resin are as mentioned above.

The silica precursor may comprise silicon alkoxide . The silicon alkoxide may be of the following formula Si(OR)_n, in which R is an Ci_₆alkyl group and n is either 3 or 4. When n is 3, the silicon alkoxide is a trialkoxysilane and may be selected from the - group consisting of trimethoxysilane , triethoxysilane, triprdpoxysilane , tributoxysilane, tripentoxysilane _. and trihexoxysilane . When n is 4, the silicon alkoxide is a tetraalkoxysilane and may be selected from the group consisting of, tetramethoxysilane, tetraethoxysilane (or commonly known as tetraethyl orthosilicate , TEOS) , tetrapropoxysilane, tetrabutoxysilane, tetrapentoxysilane and tetrahexoxysilane . In one embodiment, the silicon alkoxide is TEOS, having the structure (III) below:

(III)

The silica precursor may undergo a hydrolysis reaction to form silicon hydroxide. Hence, in one embodiment of the disclosed method, the silicon hydroxide molecules may be derived from hydrolyzing silica precursors that are provided to the substantially homogeneous mixture. The water for the hydrolysis reaction may be extracted from the alkaline .catalyst solution. Hence, the method may comprise the step of providing hydroxyl groups on the surface of silica particles or nanoparticles that are capable of condensing with the hydroxyl functional . groups of the organo-silane coupling agent .

The method may comprise the step of condensing silicon hydroxide molecules in, the presence of the alkaline catalyst to thereby form the hydrolyzed silica particles or nanoparticles.

The alkaline catalyst present in the substantially omogeneous mixture may aid in the condensation reaction between the hydrolyzed silica particles or nanoparticles and the hydrolyzed organo-silane coupling agent. The alkaline catalyst may contain an ammonium cation (when in the presence of water molecules) . Hence, the catalyst may be selected from the group consisting of ammonia, ammonium hydroxide and alkylamine such as methylamine and ethylamine. The catalyst may be capable of catalyzing the hydrolysis of silicon hydroxide to form the hydrolyzed silica particles or nanoparticles while, at the same time, catalyze the condensation reaction between the hydrolyzed silica particles or nanoparticles and hydrolyzed organo-silane coupling agent to form a surface functionalized silica particles or nanoparticles .

In the substantially homogeneous mixture, the following weight ratios may be used. The weight ratio of the organo-silane coupling agent to silica (based on ^" . theoretical estimation of the final silica content) may be in the range of 0.0001:1.0 to 0.5:1.0. The weight ratio of the polymerizable resin to silica (based on theoretical estimation of the final silica content) may be in the range of 6:1 to 610:1. The weight ratio of the silica precursor to catalyst is from 5.7:1 to 7.7:1. If the amount of catalyst added is below the volume ratio as mentioned above of 5.7:1, the silica particles or nanoparticles may not be formed completely from the silica precursor. On the other hand, if the amount of catalyst added is greater than the volume ratio as mentioned above of 7.7:1, the coupling agent would also form the silica particles or nanoparticles, which is undesirable.

The substantially homogeneous mixture may comprise an organic solvent to increase the homogeneity of mixing components and to reduce the aggregation or agglomeration of silica particles or nanoparticles. The weight ratio of solvent to polymerizable resin coated surface functionalized silica particles or nanoparticles ^' is from 0:4 to 4:4, or 1:4. The organic solvent may be an alcohol or a ketone. The organic solvent may be monohydric, polyhydric, unsaturated aliphatic or alicyclic alcohols. The organic solvent may be polar protic or polar aprotic . The organic solvent may be ethanol or acetone. The organic solvent may be used in trace amounts.

In. one embodiment, the mechanism for the in- situ process . of making the surface-functionalized silica particles or nanoparticles is shown in Scheme 1 below:

Scheme 1

From Scheme 1, a silica precursor such as TEOS and an organo-silane coupling agent such as APTMS are hydrolyzed by hydroxy1 groups of H₂0 that come from an ammonia solution to form silicon . hydroxide and hydrolyzed APTMS, respectively (step 1) . . It is to be noted that the water molecules do not serve as a solvent in the homogeneous mixture, but are present in the reaction scheme as one of the reactants for this process. After that, the hydrolyzed silica particles or nanoparticles are formed via condensation reaction of silicon hydroxide molecules in the presence of the ammonia catalyst solution. The hydrolyzed silica particles or nanoparticles undergo nucleation and growth to form oval-shaped hydrolyzed silica particles or nanoparticles (as seen in step 2) . The hydrolyzed APTMS molecules and hydrolyzed silica particles or nanoparticles then undergo a condensation reaction in the presence of the ammonia catalyst solution to form surface-functionalized silica particles or nanoparticles such as surface-aminated silica particles or nanoparticles (step 3). In. this condensation step, the NH₃ molecules act as a catalyst to accelerate the condensation of hydrolyzed TEOS and APTMS . These NH₃ molecules are recovered back after the condensation reaction because it serves as a catalyst.

Based on Scheme 1, if the ammonia solution is not present, the silica particles or nanoparticles would not be formed because the water molecules (H₂0) and alkaline catalyst (NH₃_ molecules) are requisite components for this step. In the absence of NH₃ molecules (that is, only water is present) , the nucleation and growth mechanisms of the hydrolyzed silica particles or nanoparticles will be affected, resulting in non-homogeneous silica dispersion, large aggregation of silica and non-uniform morphology of silica particles or nanoparticles in the polymerizable resin. Therefore, NH₃ molecules may be necessary in order to achieve elongated silica particles or nanoparticles that are uniformly dispersed and have a substantially uniform morphology in the polymerizable resin.

The silica particles or nanoparticles may be monodispersed in the polymerizable resin as discrete, individual particles.

The average particle size of the silica particles or nanoparticles may be controlled by controlling the nucleation number, which is in tur controlled by the process kinetics and temperature. As will be mentioned further below, , as the silica particles or nanoparticles are being formed, the silica particles or nanoparticles are subjected to a shear environment. Hence, the method may comprise the step of generating a shear environment during mixing of . said homogeneous mixture . The shear environment may be generated by agitating the substantially homogeneous mixture. The agitating step aids in substantially preventing the aggregation of the silica nanoparticles such that they stay in the nano-scale and do not form micro-particles. The silica particles or nanoparticles may also be stabilized due to the linkage with the polymerizable resin.

The silica particles or nanoparticles may have an elongated shape with an aspect ratio (that is, the ratio of the length to the width of the silica particles or nanoparticles) in the range of more than 1 to about 5. The elongated or oblong shape of the silica particles or nanoparticles may be due to the stretching of the silica particles or nanoparticles as they are being formed in a shear environment. The shear environment may be a high shear environment. The high shear may be generated as the reaction mixture is subjected to agitation such as vigorous stirring in a reaction, vessel, leading to the creation of turbulent conditions in the reaction vessel.

For turbulent flow, the Reynolds number is greater than 10 , 000.

. Hence, the method may comprise the step of agitating the silica particles or nanoparticles during manufacture to impart a shear force therein.

The method may ..comprise the step of selecting a mixing temperature in the range of about 20°C to about

60°C. The mixing temperature may be selected from the range of about 25°C to about 60°C, about 30°C to about 60°C, about 35°C to about 60°C, about 0°C to about 60°C, about 45°C to about 60°C, about 50°C to about 60°C, about 55°C to about 60°C, about 20°C to about 25°C, about 20°C to about 30°C, about 20°C to about 35°C, about 20°C to about 40°C, about 20°C to about 45°C, about 20°C to about 50°C, and about 20°C to about 55°C. In one embodiment, the temperature is about 50°C. The temperature may be chosen to allow the mixture to be stirred easily because the polymerizable resin may be more viscous at a . igher temperature . In another embodiment , the temperature may be about 25°C (or room temperature) .

The method may comprise the step of ageing the substantially homogeneous mixture. The ageing step may be undertaken for an ageing time in the range of about 30 minutes to about 2 hours, or about 1.5 hours.

The method may comprise the step . of removing unreacted reactants and by-products from the reacted mixture. Hence, . excess ammonia catalyst, water and byproducts such as alcohols may be removed. The reacted mixture may be vacuumed at a temperature of about 70°C to about 80°C, or about 75°C to remove the above.

The polymerizable resin coated surface functionalized silica particles or nanoparticles may be dried to form a dry powder. The dry power of polymerizable resin coated surface functionalized silica particles or nanoparticles may be ground to fine particles and compounded with the. polymeric material . in melt state · to form the polymer composite or nanocomposite.

The surface functionalized silica particles or nanoparticles coated with a resin carrier may be used as a filler in a polymer composite nanocomposite. Hence, there is also provided use of surface functionalized silica particles or nanoparticles coated with a . resin carrier as a filler in a polymer composite or nanocomposite. The polymeric composite or nanocomposite may comprise a polymeric material. The polymeric material may comprise a thermoplastic polymer. The resin coated surface functionalized silica particles or nanoparticles may have a weight% in the range of 0.1 to 30 wt% in the polymer composite or nanocomposite, based on the weight of said polymeric material.

Brief Description Of Drawings

The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for . purposes of illustration only, and not as a definition of the limits of the invention.

Fig. 1 is a schematic diagram showing the method according to one disclosed embodiment to form the polymer nanocomposite.

Fig. 2 is a transmission electron micrography (TEM) image at a scale of 50 nm showing the polymerizable resin coated organo-silane functionalized silica nanoparticles. The average particle size of these nanoparticles is around

45 nm while the actual particle size varies from 45 to 100 nm.

Fig. 3 is a TEM image at a scale of 200 nm showing the dispersion of polymerizable resin coated surface functionalized - silica nanoparticles (10wt%) in polypropylene.

Fig. 4 is a graph comparing the tensile modulus and flexural modulus of a number of polymer nanocomposites from the control, Example l-10wt%, Example l-15wt%, Comparative Example 1 and Comparative Example 2.

Fig. 5 is a graph comparing the degradation temperature and glass transition temperature of a number of polymer nanocomposites from the control, Example 1- 10wt%, Example l-15wt%, Comparative Example 1 and Comparative Example 2.

Fig. 6 is a graph comparing the tensile modulus and flexural modulus of a number of polymer nanocomposites from the control, Example l-10wt%, Comparative Example 3 and Comparative Example 4.

Fig. 7 is a graph comparing the degradation temperature and glass transition temperature of a number of polymer nanocomposites from the control, Example 1- 10wt%, Comparative Example 3 and Comparative Example 4.

Detailed Description of Drawings

Referring to Fig. 1, there is a schematic diagram showing the method¹ 100 according to one disclosed embodiment to form the polymer nanocomposite.

A mixture of silica precursor 10, coupling agent 12, polymerizable resin 14 and an alkaline catalyst 16 in trace amounts of an organic solvent was placed in a shaker flask 2 making up a reaction zone. The mixture was agitated to form the polymerizable resin surface functionalized silica nanoparticles . The reacted mixture was then subjected to a vacuum atmosphere 4 to remove excess reactants and by-products. The polymerizable resin surface functionalized silica nanoparticles. were then ground to a fine powder in which the particle size of the polymerizable resin surface functionalized silica nanoparticles 6 is around 45 nm.

Following which, the polymerizable resin surface functionalized silica nanoparticles 6 are compounded 8 with a thermoplastic polymer to form the polymer nanocomposite. Examples

A non- limiting example of the invention and comparative examples will be further described in greater detail below, which should not be construed as in any way limiting the scope of the invention.

Example 1

Preparation of polypropylene nanocoitiposite using polymerizable resin coated surface functionalized silica nanoparticles as filler

Tetraethylorthosilicate (TEOS) , aminopropyltrimethoxysilane (APTMS) , Glycidyl ether of bisphenol A (D.E.R.™ 332, DOW) and ethanol with a weight ratio of 20:1:7:3 were mixed under vigorous stirring at 50°C. Ammonia solution (25 wt- NH₃ solution, 1:1.6 volume ratio of NH₃ solution: TEOS ) was injected in the above solution and aged for 1.5 hours. The excess ammonia solution and alcohols produced during the formation of silica nanoparticles were vacuumed removed from suspension at 75°C. The dried polymerizable resin coated organo-silane functionalized silica nanoparticles (as shown in Fig. 2) were ground to fine particles before compounding with thermoplastic polymer.

Polypropylene (PP, P701J from SCG Chemicals) was melt

, blended with 10wt% and 15wt% of silica to PP in a Brabender Mixer at 180°C at a screw speed of 100 rpm for 15 minutes. The compounded silica/polypropylene nanocomposites were crushed into small pieces for molding.

Fig. 3 is the TEM image of the dispersion of polymerizable resin coated organo-silane functionalized silica nanoparticles (10wt%) in polypropylene. Comparative Example 1

Preparation of polypropylene nanocomposite using surface functionalized silica nanoparticles as filler

The method of Example 1 was used here but without the addition of glycidyl ether of bisphenol A in the mixture to form organo-silane functionalized silica nanoparticles. Then 10wt% of the organo-silane functionalized silica nanoparticles was used to form the polymer nanocomposite using the same steps as those in Example 1.

Comparative Example 2

Preparation of polypropylene nanocomposite using polymerizable resin coated silica nanoparticles as filler

The method of Example 1 was used here but without the addition, of APTMS in the mixture to form polymerizable resin . coated silica nanoparticles. Then 10wt% of the organo-silane functionalized silica nanoparticles was used to form the polymer nanocomposite using the same steps as those in Example. 1.

Comparative Example 3

Preparation of polypropylene nanocomposite using silica from Cabot Corporation as filler

Polypropylene was melt blended with the commercial silica (Cabot Corporation, average particle size of 115 nm) at 10% by weight of silica to PP in a Brabender Mixer at 180°C at a screw speed of 100 rpm for 15 minutes. The compounded Cabot silica/polypropylene was air-cooled, followed by crushing into small pieces for molding. Comparative Example 4

Preparation of polypropylene nanocomposite using silica from Sigma-Aldrich as filler Polypropylene was melt blended with commercial silica

(Sigma-Aldrich, average, particle size- of 15 nm) at 10% by weight of silica to PP in a Brabender Mixer at 180°C at a screw speed of 100 rpm for 15 minutes. The compounded Aldrich silica/polypropylene was air-cooled, followed by crushing into small pieces for molding.

Control

Preparation of neat polypropylene Polypropylene was injection molded with a DACA #5000

Micro- inj ector. The molded specimens were tested and the thermal and mechanical properties were compared with the polymer nanocomposites of Example 1 and Comparative Examples 1 to .

Analytical Methods i) Thermal Properties

A. Single-cantilever mode of the dynamic mechanical analyzer (DMA Q800, TA Instruments) was used to measure dynamic modulus and glass transition temperature (Tg) of material at a frequency of 1 Hz, the temperature range was from -85°C . to 60°C at a heating rate of 3°C/min and oscillation amplitude of 20 μτα. The measurement was done under liquid nitrogen.

B. Thermogravimetric analysis (TGA) was performed with a thermogravimetric analyzer (TA instrument Q500) at a heating rate of 5°C/min to 800°C under nitrogen atmosphere to obtain degradation temperature (Td) of compounded nanocomposites .

C. Differential scanning calorimetry (DSC) was used to measure the melting temperature (T_m) and crystallization temperature (T_c) of compounded nanocomposites by increasing the temperature from -50°C to 200°C at a heating rate of 10°C/min.

ii) Mechanical Properties

A. Flexural modulus was determined by 3 -point bending test according to the ASTM Standard D 790-96. The nanocomposite was injection molded with the DACA #5000 Micro- injector. The specimen bars with dimension of 60 x 10 x 1 .mm³. The barrel and mold temperatures were set at 200°C and 70°C, respectively. The nanocomposite was held in the barrel for 4 minutes and allowed to melt. A piston driven by air pressure of 8 bars was then used to push the melt into the mold. The holding time of the piston was 7 seconds . The molded specimen bars were tested to compare the properties of silica master batch/PP at different silica contents. The tests were conducted with crosshead speed of 1 mm/min, at a span length of 40 mm.

B. Tensile modulus. The nanocomposite was injection molded with the DACA #5000 Micro-injector. The dumbbell bars with dimension of 75 x 4 x 2 mm³ were molded according to ASTM D 638-03. The barrel and mold temperatures were set at 200°C and 70°C, respectively. The nanocomposite was held in a barrel for 4 minutes and allowed to melt. A piston driven by air pressure of 8 bars was used to push the melt into the mold. The holding time of the piston was 7 seconds. The molded specimen bars were tested to compare the properties of silica master batch/PP . at different silica contents. The test was carried using the Instron 5569 testing machine at tensile speed of 1 mm/min. Using these analytical methods, characterization of the polymer nanocomposites obtained from the above example and comparative examples were carried out . Table 1 below summarizes the thermal and mechanical properties of each polymer composite.

°: Melting temperature. : Degradation temperature. ^c: Glass transition temperature

Silica/PP nanocomposite with good mechanical properties and high thermal stability are proven to be conveniently prepared by incorporating polymerizable resin coated organo-silane f nctionalized silica nanoparticles of the present invention as active nano- filler. The flexural modulus and tensile modulus of polymerizable resin coated organo-silane functionalized silica nanoparticles /PP composites with 10-15- % by weight of polymerizable resin coated organo-silane functionalized silica nanoparticles to PP (Example l-10wt% and Example 1- 15wt%) are significantly improved from neat PP (control) , organo-silane functionalized silica nanoparticles/PP (Comparative Example 1), polymerizable resin coated silica nanoparticles/PP (Comparative Example 2) as well as commercial silica/PP nanocomposites (Comparative Examples 3 and 4) . This is also observed in Fig. 4 in which a 35% increase in the tensile and flexural modulus is observed is., the polymer nanocomposites of Example 1 as compared to the control, while in Fig. 6, there was a^' 10 to 38% increase in the tensile and flexural modulus as compared to Comparative Examples 3 and 4.

The thermal stability of neat PP (control) "is enhanced by the method of the present invention, wherein higher degradation temperature (T_d) and glass transition temperature (T_g) are increased with the amount of polymerizable resin coated organo-silane functionalized silica nanoparticles in PP (Example l-10wt% and Example 1- 15wt%) . This is in comparison to the comparative example samples in which the degradation temperature actually decreases as . compared to the control. This is seen in Fig. 5 in which the polymer nanocomposites of Example 1 have an improvement in the degradation temperature while the glass transition temperature is comparable with the control, while Fig. 7 shows that the polymer nanocomposites of Example 1 have higher thermal stability and higher glass transition temperature than those of Comparative Examples 3 and 4.. Therefore, the polymer nanocomposite disclosed herein. has superior properties and is applicable for wide ranges of industrial applications.

.Applications

The surface functionalized silica particles or nanoparticles coated with a resin carrier may be used as a filler for a polymer composite or nanocomposite. The resultant polymer composite or nanocomposite may have improved thermal and mechanical . properties . Hence , the disclosed filler may be used for wide ranges of thermoplastic polymer applications. The filler present in the polymer composite or nanocomposite may be formed under mild conditions and in a short reaction period. The filler may be formed in situ and in a single - step, which in turn leads to lower manufacturing costs. Hence, the filler may be formed in a simpler and lower cost method, which enables the production process of the filler and the resultant polymer nanocomposite to be scaled up to large-scale manufac uring .

The filler content in the polymer composite or nanocomposite may be low (about 0.1wt% to 30wt%) .

The polymer composite or nanocomposite may be used as structural components of automobiles, sporting goods, electronic industries and in packaging.

It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

1. A polymer composite comprising a plurality of surface functionalized silica particles dispersed in a polymeric material, wherein said surface functionalized silica particles are at least partially coated with a resin carrier.

2. The polymer composite of^■ claim 1, wherein said surface functionalized silica particles are amine functionalized silica particles.

3. The polymer composite of claim 1 or claim 2, wherein said resin carrier comprises a thermosetting polymer.

4. The polymer composite of claim 3, wherein said thermosetting polymer comprises an epoxy matrix material. .

5. The polymer composite of claim 4, wherein said epoxy matrix material comprises an epoxy-containing monomer, oligomer, polymer or combinations thereof.

6. The. polymer composite of any one of the preceding claims, wherein said polymeric material comprises a thermoplastic polymer.

7. The polymer composite of claim 6, wherein said thermoplastic polymer comprises monomers selected from the group consisting of acrylates, phthalamides , acrylonitriles , cellulosics, styrenes, alkyls, alkyls methacrylates , alkenes, halogenated alkenes, amides, imides,' aryletherketones , butadienes, ketones, esters, acetals, acetates, sulfones, polyols, isocyanates, carbonates and combinations thereof.

8. The polymer composite of claim 6 or 7 , wherein said thermoplastic polymer is selected from the group consisting . of poJ p^'ropyl^'ene, pol ethyIme? . polystyrene , polyamide, polybutylene , poly (vinyl chloride)^', ethylene vinyl acetate, polyethylene terephthalate , polysulfone, polyurethane and combinations thereof .

9. The polymer composite of any one of the preceding claims, wherein the average particle size of the silica particles coated by the polymerizable resin is less than 1000 nm.

10. The polymer composite of claim 9, wherein said average particle size is in the range of 10 nm to 500 nm.

11. The polymer composite of any one of the preceding claims, wherein said resin coated surface, functionalized silica nanoparticles is present in said polymer nanocomposite at a weight% in the range of 0.1 to 30 wt%, based on the weight of said polymeric material.

12. The polymer composite of claim 11, wherein said weight% is in the range of 0.1 to 15 wt% .

13. A method for forming a polymer composite of any one of the preceding claims, comprising the step of compounding ^'a plurality of polymerizable resin coated surface functionalized silica particles with a polymeric material.

14. The method of claim 13, wherein said compounding step comprises the step of selecting a compounding temperature in the range of 150°C to 200°C.

15. The method of claim 13 or claim 14, wherein said compounding step comprises the step of selecting a compounding time in the range of 5 minutes to 30 minutes.

16. The method of any one of claims 13 to 15, comprising, before said compounding step, the step of manufacturing said polymerizable resin coated surface functionalized silica particles.

17. The method of claim 16, wherein said manufacturing step comprise the step of mixing a substantially homogeneous mixture of silica precursors, a polymerizable resin, a coupling agent having, functional groups and an alkaline catalyst under conditions to produce polymerizable resin coated surface functional!zed silica particles.

18. The method of claim 17, wherein said mixing step comprises the step of generating a shear environment.

19. The method of claim 18, wherein said generating step comprises the step of agitating said substantially homogeneous mixture .

20. The method, of any one of claims 17 to 19, wherein said mixing step comprises the step of selecting a mixing temperature in the range of 20°C to 60°C.

21. The method of any one of claims 17 to 19, comprising the step of ageing said mixture.

22. The method of claim 21, wherein said ageing step comprises the step of selecting an ageing time in the range of 30 minutes to 2 hours.

23. The method of any one of claims 17 to 22, further comprising the step of reducing the particle size of said polymerizable resin coated surface functronalized silica particles.

24. The method of claim 23, wherein said reducing step comprises the step of grinding said polymerizable resin coated surface f nctionalized silica particles.

25. Use of surface functionalized silica particles coated with a resin carrier as a filler in a polymer composite.

26. The use of claim 25, wherein said polymer composite comprises a polymeric material.

27. The_ use of claim 26, wherein said polymeric material comprises a thermoplastic polymer. ^" 28. The use of claim 26 or 27, wherein said resin coated surface functionalized silica nanoparticles have a weight% in the range of 0.1 to 30 wt% in said polymer composite, based on the weight of said polymeric material .