Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/16—Making expandable particles
  • C08J9/20—Making expandable particles by suspension polymerisation in the presence of the blowing agent
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
  • C08J9/12—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a physical blowing agent
  • C08J9/125—Water, e.g. hydrated salts
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K3/00—Use of inorganic substances as compounding ingredients
  • C08K3/34—Silicon-containing compounds
  • C08K3/346—Clay
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2325/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Derivatives of such polymers
  • C08J2325/02—Homopolymers or copolymers of hydrocarbons
  • C08J2325/04—Homopolymers or copolymers of styrene
  • C08J2325/08—Copolymers of styrene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L25/00—Compositions of, homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring; Compositions of derivatives of such polymers
  • C08L25/02—Homopolymers or copolymers of hydrocarbons
  • C08L25/04—Homopolymers or copolymers of styrene
  • C08L25/08—Copolymers of styrene

Definitions

• the present invention relates to a process for the preparation of a water expandable polymer beads (WEPS).
• WEPS water expandable polymer beads
• EPS expandable polystyrene beads
• pentane as the blowing agent.
• the application of pentane and its isomers results in homogeneous EPS foams of low density.
• pentane or its isomers is the harmfulness to the
• styrenesulfonate or block copolymers comprising polystyrene blocks and poly(styrene sulfonate) blocks. All of these substances exhibit both a hydrophilic and a hydrophobicmoiety and are thus capable of emulsifying water in styrene.
• US6160027 describes the preparation of beads consisting of polystyrene homopolymer.
• An additional emulsifier preferably sodium bis(2- ethylhexyl)sulfosuccinate: AOT
• AOT sodium bis(2- ethylhexyl)sulfosuccinate
• the problem of using emulsifiers with long linear alkyl chains is that the miscibtlity of these aliphatic emulsifier tails with the aromatic styrene/polystyrene phase decreases with increasing conversion of the styrene/polystyrene mixture.
• surfactant rich domains are formed which will subsequently negatively affect water droplet size and shape.
• coalescence of dispersed, water droplets will eventually occur.
• the eventual result is a phase separation between the water phase and the styrene/polystyrene phase.
• emulsifiers such as AOT may have negative influence on the suspension stability.
• the styrene/polystyrene viscous droplets containing emulsified water may consequently change in shape and size to result in non-spherical beads.
• the present suspension water that is used as medium to disperse the styrene/polystyrene droplets may become fully emulsified as small water droplets in a continuous styrene/polystyrene phase (inverse emulsion).
• montmorillonite nanoclay is described. WEPS foams with a density of less than 50 kg/m 3 were obtained. According to these publications, the montmorillonite nanoclay forms a layer around the cell wall during foaming of the WEPS beads. This layer reduces free diffusion of water out of the bead during the foaming procedure so that more water is available for expansion and hence larger expansion ratios are obtained. Emulsifiers such as AOT mayhave a negative influence on the suspension stability.
• step d) suspending the inverse emulsion obtained by step c) in an aqueous medium to yield an aqueous suspension of suspended droplets and
• emulsifiers used for the preparation of water-expandable polymer beads in the prior art are sorbitan carboxylates, sorbitol or mannitol carboxylates, glycol or glycerol carboxylates, alkanolamides, alkyl phenols and dialkyl ethers (any of which emulsifiers may or may not contain a polyalkoxy chain with 1 to 20 oxyalkylene groups).
• emulsifiers used for the preparation of water-expandable polymer beads are salts of long chain (C8 -C30) carboxylic acids, long chain (C8-30) alkyl sulphonic acid, Other known emulsifiers used for the preparation of water-expandable polymer beads are alkylarylsulphonic acid, sulphosuccinic acid, high-molecular-weight fatty amines, ammonium or other nitrogen derivatives of long chain carboxylic acids.
• emulsifier-free process is herein meant a process in which the monomer composition includes no or little amount, e.g. less than 0.01 wt% (with respect to the monomers in the monomer composition), of the emulsifiers mentioned in the preceding paragraph.
• styrene and a polar comonomer are copolymerized.
• the polar comonomer allows the
• nanoclay increases the water uptake, but in the cases where only styrene was used as the monomer and the nanoclay is added, the water droplets inside the WEPS beads are rather large and inhomogeneously distributed. Similarly, when only the polar monomer is used without the nanoclay, the water droplets inside the WEPS beads are large and inhomogeneously distributed.
• the use of the polar comonomer and the nanoclay in combination resulted in polymer beads with a high water uptake in which a homogeneous distribution of the nanoclay/water dispersion is achieved.
• the addition of the nanoclay dispersion should be done after some portion of the monomers have been converted to copolymer. Without wishing to be bound by any theory, it is thought that the viscosity of the prepolymer mixture has to be sufficiently high prior to addition of the dispersion of nanoclay. Water droplet coagulation and inhomogeneous droplet distribution may occur when the nanoclay dispersion is added to a low viscous reaction mixture.
• the degree of conversion from the monomers to copolymer is preferably 20 to 55%, based on the monomers.
• the conversion rate can be determined by evaporating the volatile monomers from a sample of the reaction mixture of a known weight and measuring the residual weight of the non-volatile copolymer.
• the sample may be dried e.g. at 60 °C for at least 24 hours under vacuum for the evaporation.
• the nanoclay used in the present invention is a modifier-free nanoclay. It was found that modified nanoclays resulted in a decreased
• Modifier-free nanoclays used in the present invention are not particularly limited and include modifier-free nanoclays such as sodium montmorillonite (Na + MMT), and calcium montmorillonite (Ca 2+ MMT), which can be synthetic or natural. Although calcium montmorillonite typically exists as aggregates formed of layered structures, the aggregates can be exfoliated in a water-based solution.
• the nanoclay is Na + MMT. It is to be appreciated that layered talc minerals may be included in addition to, or in place of, the modifier- free nanoclays, and such embodiments are considered to be within the purview of this invention.
• the nanoclay is Na + MMT. It is to be appreciated that layered talc minerals may be included in addition to, or in place of, the modifier- free nanoclays, and such embodiments are considered to be within the purview of this invention.
• the nanoclay is Na + MMT. It is
• Nanocor PGV nanocor PGV and has an aspect ratio of 150-200 and a maximum moisture uptake of 18 wt%.
• the polar comonomer containing a carbon-to-carbon double bond may be selected from a wide range of monomers as long as it can be
• polar as referred to herein is well-known to the skilled person in the art; for instance, a polar molecule is defined in the prior art as a molecule having a permanent electric dipole moment or polarity refers in the prior art to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment, molecular polarity being typically dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure; the polar molecules interact through dipole-dipole intermolecular forces and hydrogen bonds (see e.g.
• a polar comonomer as referred to in the present invention can be defined thus as a molecule comprising at least one carbon to carbon double bond together with at least two atoms of different electronegativities forming a covalent bond with each other.
• Examples of the polar comonomer containing a carbon-to-carbon double bond may be represented by the comonomer of formula (1),
• R stands for H or for an alkyl having 1 to 3 C-atoms
• R 2 stands for H or for a carboxylic acid
• R 3 stands for H or for an optionally substituted alkyl having 1 to 6 C-atoms
• R 4 stands for a polar group selected from the group consisting of a carboxylic acid group (COOH), a carboxylic acid amide group connected via the C- atom (C(0)NH 2 ), a carboxylic acid amide group connected via the N-atom
• R 2 and R 4 may form a ring together with the C-atoms to which they are bound and wherein R 3 and R 4 may form a ring together with the C-atoms to which they are bound
• R preferably stands for H or methyl.
• R 2 preferably stands for H.
• R 3 may stand for an optionally substituted alkyl having 1 to 6 C- atoms, preferably for H, methyl, ethyl or i-propyi;
• Substituents include polar groups, such as for example a carboxylic acid group (COOH), an amine group (NH 2 ), an amide group (C(0)NH 2 ) and a hydroxyl group (OH).
• R may stand for a carboxylic acid alkyl ester having 2 to 4 C-atoms substituted with a polar group R 7 , wherein R 7 stands for a hydroxyl group (OH), an amine group (NH 2 ), a carboxylic acid group (COOH), for example for a carboxylic acid methyl ester or for a carboxylic acid ethyl ester.
• R 2 and R 4 may form a ring together with the C-atoms to which they are bound; for example a ring containing a heteroatom, for example N or O.
• R 3 and R 4 may form a ring together with the C-atoms to which they are bound, for example a ring containing a heteroatom, for example N or 0.
• Examples of the polar comonomer of formula (1 ) include but are not limited to acrylic acid (R 1 , R 2 and R 3 stand for H and R 4 stands for a carboxylic acid group), methacrylic acid (R 1 and R 2 stand for H, R 3 stands for methyl and R 4 stands for a carboxylic acid group), propyl acrylic acid (R 1 and R 2 stand for H, R 3 stands for i-propyl and R 4 stands for a carboxylic acid group), maleic acid or citraconic acid (R 1 and R 3 stand for a carboxylic acid group and R 2 and R 4 stand for H), itaconic acid (R 1 and R 2 stand for H, R 3 stands for methyl substituted with a carboxylic acid group and R 4 stands for a carboxylic acid group), measconic acid (R 1 stands for methyl, R 2 stands for a carboxylic acid group, R 3 stands for H and R 4 stands for a carboxylic acid group), acrylamide (R 1 , R 2 and R 3
• the amount of the polar comonomer with respect to styrene influences the water droplet distribution, as well as the degree of the emulsification of water in the prepolymer composition.
• the weight ratio of styrene and the polar comonomer in the monomer composition is preferably between 99:1 to 70:30.
• the combination of styrene, HEMA and nanoclay showed a particularly large increase in the water entrapment compared to the combination of styrene and HEMA without the use of nanoclay.
• the pores containing water droplets present in the beads are small.
• the weight ratio of styrene and HEMA in the monomer composition is preferably between 95:5 to 85:15. This range was found to result in a highly uniform distribution of water droplets in the WEPS beads, which may lead to large expansion ratios.
• a further advantage of such PSPHEMA copolymers comprising up to 15 wt% of HEMA is that they have a single glass transition temperature Tg. This improves homogeneous expansion upon heating.
• the weight ratio of styrene and methacrylic acid in the monomer composition is preferably between 99:1 to 90:10, preferably 98:2 to 94:6.
• the pores containing water in the PSPMAA beads showed a homogeneous distribution in the beads, i.e. the pores were present evenly in the center of the beads and closer to the surface.
• the weight ratio of styrene and acrylic acid in the monomer composition is preferably between 99:1 to 90:10, preferably 98:2 to 94:6
• the amount of the nanoclay is preferably 0.1 -10 wt% with respect to the total weight of the monomers in the monomer composition, more preferably 0.1 -1.5 wt%, more preferably 0.1 -1.0 wt%, more preferably 0.3-1.0 wt%. Even more preferably, the amount of the nanoclay is 0.5-1.0 wt%. This range of nanoclay results in a particularly improved water uptake.
• the amount of the nanoclay in the aqueous dispersion used in step c) is preferably 1 -10 wt%. This range allows making a homogeneous dispersion of nanoclay.
• the monomer composition comprises styrene and a polar comonomer which results in a copolymer of styrene and the polar comonomer.
• the monomer composition may further comprise a
• the monomer composition does not contain an emulsifier, i.e. the monomer composition is an emulsifier-free composition.
• the cross-linking agent is selected from the group of compounds having at least two olefinic double bonds.
• examples of such compounds include divinyibenzene (or a mixture of its isomers), a, c )-alkadienes, e.g. isoprene, the diester of acrylic acid or methacrylic acid with a diol, such as ethylene glycol,butanediol, pentanediol or hexanediol.
• divinyibenzene or a mixture of its isomers
• a, c )-alkadienes e.g. isoprene
• the diester of acrylic acid or methacrylic acid with a diol such as ethylene glycol,butanediol, pentanediol or hexanediol.
• the amount of the cross-linking agent should not be too low. On the other hand, if the amount of cross-linking agent would be too high, the expandability of the eventual particles would be deteriorated.
• a suitable range is from 0,01 to 5% wt, preferably from 0.01 to 1.5% wt, more preferably 0.01 to 0.5 wt%, based on the amount of monomers. Most preferably from 0.01 to 0.1 % wt of cross-linking agent is used.
• cross linking agent improves the mechanical properties of the expanded beads resulting from the WEPS of the present invention. After the beads are compressed and the pressure is released, the increase of the thickness was found to be larger than the beads in which no cross linking agent was used.
• the polymerization initiator can be selected from the conventional initiators for free-radical styrene polymerization. They include in particular organic peroxy compounds, such as peroxides, peroxycarbonates and peresters.
• peroxy compounds can also be used.
• suitable peroxy initiators are C6 -C20 acyl peroxides such as decanoyl peroxide, benzoyl peroxide, octanoyl peroxy, stearyl peroxide, 3,5,5-trimethyl hexanoyl peroxide, per-esters of C2 -C18 acids and C1 -C5 alkyl groups, such as t- butylperbenzoate, t-butylperacetate, t-butyl-perpivalate, t-butylperisobutyrate and t-butyl-peroxylaurate, and hydroperoxides and dihydrocarbyl (C3 -C10)peroxides, such as diisopropylbenzene hydroperoxide, di-t-butyl peroxide, dicumyl peroxide or combinations thereof.
• temperatures above 100 °C are used for suspension polymerization, typically
• Radical initiators different from peroxy compounds are not excluded.
• a suitable example of such a compound is ⁇ , ⁇ '-azobisisobutyronitrile.
• the amount of radical initiator is suitably from 0.01 to 1% wt, based on the weight of the monomers.
• the monomer composition may further contain other additives in effective amounts.
• additives include dyes, fillers, flame retarding compounds, nucleating agents, antistatic compounds and lubricants.
• the monomer composition is subjected to a prepolymerization step to obtain a mixture of styrene, the polar comonomer and their copolymer.
• the monomer composition may be added to a reactor, e.g. a double-walled reactor equipped with motorized stirrer, reflux cooler, temperature sensor and nitrogen inlet.
• the reactor may be purged with a nitrogen flow of e.g. 0.5 L/min during the whole reaction.
• the stirring speed is set to an appropriate speed, e.g. at 300 rpm.
• the monomer composition is heated to the reaction temperature to obtain a prepolymer composition.
• the reaction temperature depends e.g. on the type of the initiators. For example, when benzoyl peroxide is used as the initiator, the reaction temperature is preferably chosen to be in the range of 80 to 90 °C. More preferably, the reaction temperature is chosen to be in the range of 85 to 90 °C. In the cases where azo type initiators are used, the reaction temperature may be chosen to be lower than 80 0 C, e.g. 70-80 °C.
• the reaction temperature is chosen to control the reaction rate to an appropriate level. When the temperature is too low, the reaction the overall reaction rate is too low. Similarly, when the temperature is too high, the overall reaction rate becomes too high. Especially in the cases where the polar comonomer is acrylic acid, an increased reaction rate was observed which becomes more difficult to control.
• the reaction mixture is subsequently held at the reaction temperature e.g. for 30-120 minutes.
• the reaction time is 45-90 minutes, more preferably 75-90 minutes.
• Particularly preferred is heating at a temperature of 85-90 °C for 75-
• the degree of conversion of the prepolymer composition to which the nanoclay dispersion is added is preferably 20 to 55 %, based on the monomers.
• the degree of conversion can be determined by evaporating the volatile monomers from a sample of the reaction mixture of a known weight and measuring the residual weight of the non-volatile copolymer. Before evaporating the volatile monomers from the sample, a few mg of hydroquinone is added to quench the reaction. The sample may be dried e.g. at 60 °C for at least 24 hours under vacuum for the evaporation.
• the nanoclay is mixed with the prepolymer composition as an aqueous dispersion.
• the aqueous dispersion of the nanoclay may be obtained by high shear mixing and ultrasonification.
• an aqueous medium containing the nanoclay is subjected to a high shear mixing of 15000-20000 rpm for 30 minutes followed by ultrasonification of 750 W for 30 minutes. It will be appreciated that suitable rates and time depend on the type and the size of high shear mixer to a large degree. These steps may be performed at room
• an inverse emulsion of nanoclay/water in the prepolymer composition is obtained, i.e. droplets of a mixture of nanoclay and water are dispersed in the prepolymer composition.
• the inverse emulsion is kept isothermally for some time, e.g. 20-40 min at or close to the reaction temperature, e.g. at 90 °C.
• the inverse emulsion obtained by step c) is suspended in an aqueous medium.
• the aqueous medium may be added to the inverse emulsion while stirring.
• the aqueous medium contains a suspension stabilizer. Any conventional suspension stabilizer may be used, such as polyvinylalcohol, gelatine, polyethyleneglycol, hydroxyethylcellulose, carboxymethylcellu!ose, polyvinylpyrrolidone, polyacrylamide, but also salts of poly(meth)acrylic acid, phosphonic acid or (pyro)phosphoric acid, maleic acid, ethylene diamine tetracetic acid, and the like, as will be appreciated by the person skilled in the art.
• Suitable salts include the ammonium, alkali metal and alkaline earth metal salts.
• An advantageous example of such a salt is tricalcium phosphate.
• the stabilizing agent is based on polyvinylalcohol.
• the amount of the stabilizing agents may suitably vary from 0.05 to 1.2, preferably from 0.15 to 0.8% wt, based on the weight of the water.
• the volume ratio between the aqueous medium and the prepolymer composition may vary between wide ranges, as will be appreciated by a person skilled in the art. Suitable volume ratios include 1 :1 to 1 :10 (prepolymer composition: aqueous suspension). The optimal ratio is determined by economic considerations.
• the aqueous medium has a temperature close to the inverse emulsion. This avoids the temperature decrease of the inverse emulsion after addition.
• the suspension is subjected to suspension polymerization.
• the temperature of this polymerization step may depend on the pressure at which this polymerization step is performed. When this step is performed in at atmospheric pressure, the temperature is preferably 85-90 °C. The temperature is preferably at least as high as the prepolymerization step b).
• the polymerization is preferably performed for a period of 180-360 min, more preferably 200-270 min. When this step is performed at a higher pressure, the temperature may be higher. For example, at a pressure of 4 bars, the step may be performed at a temperature of up to 125-130 °C.
• the polymerization is preferably performed in this case for a period of up to 410 minutes.
• steps a)-e) can be performed in the same reactor. This provides a simple process compared e.g. to the processes in which the prepolymerization step and the polymerization step are performed in different reactors.
• the reactor may be a glass reactor where one can look inside, or a pressurized reactor made of e.g. a stainless steel,
• the expandable polymer beads may further be coated with a coating composition for suppressing the diffusion of water out of the beads.
• a coating composition for suppressing the diffusion of water out of the beads examples include compositions containing glycerol- or metal carboxylates. Such compounds reduce the tendency of the particles to
• Suitable carboxylates are glycerol mono-, di- and/or tristearate and zinc stearate.
• Examples for such additive composition are disclosed in GB-A- 1 ,409,285.
• Particularly useful coating composition comprises wax, especially paraffin wax.
• the coating composition are deposited onto the particles via known methods e.g. via dry-coating in a ribbon blender or via a slurry or solution in a readily vaporising liquid.
• the present invention also relates to water expandable polymer beads obtainable by the present invention.
• the present invention also relates to water expandable polymer beads comprising a copolymer of styrene and a polar comonomer containing a carbon-to-carbon double bond and a modifier-free nanoclay.
• the polar comonomer may be any of the polar comonomer described above.
• the polar comonomer may be 2-hydroxyethyl methacrylate and the weight ratio of styre and 2-hydroxyethyl methacrylate in the monomer composition may be between 99:1 to 70:30, preferably 95:5 to 85:15.
• the polar comonomer may be methacrylic acid and the weight ratio of styrene and methacrylic acid in the monomer composition may be between 99:1 to 90:10, preferably 98:2 to 94:6.
• the polar comonomer may be acrylic acid and the weight ratio of styrene and acrylic acid in the monomer composition may be between 99:1 to 90:10, preferably 98:2 to 94:6.
• the water expandable polymer beads according to the present invention preferably has an average diameter of 0.1 to 3 mm, preferably from 0.4 to 3 mm .
• the expandable particles can be prefoamed by hot air or by using (superheated) steam, to yield expanded or pre-expanded particles.
• Such particles have a reduced density, e.g. from 800 to 30 kg/m 3 . It will be appreciated that in order to vaporize the water included in the particles to effect foaming, the temperature must be higher than used for C3 -C6 hydrocarbon foaming agents which have a lower boiling point than water. Foaming can also be effected by heating in oil or by using microwaves.
• the present invention also relates to expanded polymer beads obtainable by expanding the water expandable polymer beads according to the present invention.
• Fig. 1 (a) is a graph of a DSC heating run of the PSPHEMA prepared according to Ex. 4 of the present invention
• Fig. 1 (b) is a graph of a DSC heating run of an example of the PSPMAA prepared according to Ex. 6 of the present invention
• Fig.2(a) shows a SEM image of an example of the expandable PS bead according to Comp. Ex. C;
• Fig.2(b) shows a SEM image of an example of the expandable PSPMAA bead prepared according to Ex. 6 of the present invention
• Fig.2(c) shows a SEM image of an example of the expandable PSPHEMA bead prepared according to the present invention
• Fig.2(d) shows a SEM image of a further example of the expandable PSPHEMA bead prepared according to Ex. 4 of the present invention
• Fig. 2(e) shows a SEM image of an example of an expandable
• PSPHEMA bead prepared without the use of nanoclay
• Fig. 2(f) shows a SEM image of an example of an expandable
• PSPMMA bead prepared without the use of nanoclay
• Fig. 3(a) shows a SEM image of an example of the expanded
• Fig. 3(b) shows a SEM image of an example of the expanded
• Fig. 3(c) shows a SEM image of an example of the expanded
• PSPHEMA beads prepared according to Ex. 4 of the present invention.
• the monomers styrene (Sty), methacry!ic acid (MAA) and 2- hydroxyethyl methacrylate (HEMA) were obtained from Aldrich and used as received.
• the initiator benzoyl peroxide contained 25 wt% water and was also supplied by Aldrich.
• Nanoclay was Nanocor PGV from Nanocor. Nanocor PGV has an aspect ratio of 150-200 and a maximum moisture uptake of 18 wt%.
• Table 1 shows an overview of the composition feeds used in the experiments.
• the synthesized polymer beads (sometimes referred herein as
• PSPHEMA WEPS beads
• Sty/HEMA mixtures and PSPMAA for copolymers prepared from Sty/MAA mixtures are included in the abbreviation.
• a PSPHEMA95/05_0.42%PGV copolymer is prepared from a monomer feed consisting of 95 wt% Sty and 5 wt% HEMA.
• a dispersion of 0.42 wt% (with respect to the total amount of the monomers) of PGV (2.5 g) in 50 ml water is added to the prepolymer mixture during the reaction.
• the amount of PGV nanoclay varied between 0.375-0.63 wt% based on the total monomer weight.
• monomers Sty and HEMA were mixed using weight percentages: 95-5 and 90-10 wt%, respectively.
• Monomers Sty and MAA were mixed using weight percentages: 97.5-2.5 and 95-5 wt%, respectively.
• the amount of cross-linking agent divinylbenzene (DVB) varied between 0.05-0.08 wt% with respect to the total amount of the monomers.
• PGV nanoclay was homogenized in water using a combination of high-shear mixing (IKA Ultra-Turrax T8) and ultrasonification (Sonics Vibra Cell) (see procedure in Table 4).
• Table 3 Synthesis steps used in the preparation of WEPS beads containing PGV nanociay
• PSPHEMA95/05_ 0.42%PGV was prepared in the following manner. First, 2.50 g nanoclay (Nanocor PGV from Nanocor) was dispersed in 50 g water using a high shear mixer (IKA Ultra-Turrax T8) and an ultrasonic probe (Sonics Vibra Cell) (step A). The dispersing procedure is summarized in Table 4. In addition, 1200 g water containing 4.8 g (0.4 wt%) polyvinyl alcohol) (Mowiol 40-88) was placed in a beaker and subsequently heated stepwise to 90 °C (step B). The monomers Sty and HEMA together with initiator DPBO and cross-linking agent DVB were added to a double-walled reactor, equipped with motorized stirrer, reflux cooler, temperature sensor and nitrogen inlet (step C)).
• the reactor was purged with a nitrogen flow of 0.5 IJmin during the whole reaction.
• the stirring speed was set at 300 rpm and the reaction
• step K The reaction mixture was cooled down to 50 °C (step K) and the beads were collected by filtering the reaction product over a polyester sieve of 80 ⁇ . The outside of the polyester sieve was wiped off with tissue paper. The beads were subsequently take from the polyester sieve and placed into a drying oven at 50 °C without vacuum for 3.5 h to remove the water on the outside of the beads as much as possible.
• DSC Differential scanning calorimetry
• the samples were dried for 24 h in an oven under vacuum at 60 °C to remove the entrapped water inside the beads.
• the temperature was varied between -50 and 150 °C using heating and cooling rates of 10 °C/min and isothermal periods of 2 min at -50 and 150 °C, respectively. Only the second DSC heating run was evaluated.
• the second DSC heating runs of PSPHEMA90/10_0.42%PGV (Ex.4) and PSPMAA97.5/2.5 (Ex.6) are shown in Figure 1 (a) and 1 (b), respectively.
• the amount of water inside the synthesized beads was determined by Karl Fischer titration. For most batches listed in Table 1 , 8.3 wt% water (based on the total amount of monomer) was added to the prepolymer mixture. If all added water is entrapped inside the beads, then 7.7 wt% water will be theoretically present with respect to the total weight of polymer, water and nanoclay.
• the beads were dried in such a way that water present on the surface will be removed as much as possible, but water inside the bead should be retained. All samples were therefore dried for 3.5 h in an oven at 50 °C (without vacuum). The beads were no longer sticky when being removed from the oven. However, there is always equilibrium between water inside and on the surface of the bead so that after some storage time, the beads become sticky again. This thin film of water that is present on the surface can be considered to be similar and thus comparison can be made between the different samples.
• Table 6 gives an overview of the synthesized batches and the corresponding measured water contents. After drying in the oven, the beads were sieved into 3 fractions: 400-600 pm, 600-800 pm, 800-1180 pm. For each fraction, the entrapped amount of water was determined. From Table 6, it can be seen that the amount of entrapped water is dependent on the bead size. Smaller beads have a higher surface/volume ratio so that relatively more water is evaporated during the residence time in the oven compared to large beads. As a consequence, small beads will normally contain less water after drying than large beads from the same batch. For most batches, the entrapped amount of water is smaller than the amount of water that can be theoretically present (7.7wt%). Table 6 Water contents for the synthesized WEPS batches containing PGV nanoclay.
• Comp. Ex. G was prepared in the same manner as Ex. 4 except for that no nanoclay was used and that the prepolymerization step was performed at a temperature of 85 °C instead of 88-89 °C. It can be seen that the water contents in the beads according to the present invention is generally higher than in the beads according to the
• FIG. 2(a)-(f) shows a cross section of a bead from the Comp. Ex. C (PS_0.4%PGV) batch. Large holes can be seen all over the surface of the cross-section. These holes originate from water droplets which are entrapped inside the bead. It can be seen that the holes are not randomly distributed over the surface.
• Figure 2(b) shows the cross section of a
• Figure 2(c) shows the cross section of a
• Figure 2(e) shows the cross section of a WEPS bead prepared without the use of nanoclay.
• the monomers used for making the bead was styrene and MAA with a weight ratio of 95:5 (PSPAA95/05). It can be seen that the water droplets inside the WEPS beads are large and inhomogeneously distributed.
• Figure 2(f) shows the cross section of a WEPS bead prepared without the use of nanoclay.
• the monomers used for making the bead was styrene and HEMA with a weight ratio of 85:15 (PSPHEMA85/15). It can be seen that the number of holes on the surface is limited. Although the holes are more randomly distributed than for the PSPAA95/05 sample of Figure 2(d), some holes are rather large and may therefore not result in homogeneous foam after expansion.
• the foaming temperature used for foaming of the WEPS beads was approximately 120-130 °C.
• the compressibility of expanded WEPS beads was examined by compressing the beads between finger and thumb.
• the thickness of the expanded beads was measured before and after compression (Lcompressed).
• Ex. 1-2 resulted in a smoother surface of the beads compared to Ex.
• Figure 3(a) shows the cross section of an expanded WEPS bead of Ex. 6 in which MAA was used as the comonomer.
• the beads have been successfully expanded. However, large cells are visible in the center of the bead, whereas smaller cells can be observed closer to the edge.
• Figure 3(b) shows the cross section of an expanded WEPS bead in which 5wt% of HEMA was used as the comonomer.
• the beads have been successfully expanded. Some large cells are visible, but the largest fraction of cells is collapsed.
• Figure 3(c) shows the cross sectional area of a WEPS bead of Ex. 4 in which 10 wt% of HEMA was used as the comonomer.
• the beads have been successfully expanded. Small cells are present all over the surface of the cross section. Consequently, the original morphology as shown in Figure 2(d) shows that the criterion to obtain foams with a uniform cell structure is to have WEPS beads with a homogeneous distribution of small water droplets throughout the bead.

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• 2012
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