Water expandable polymer beads containing latex particles

Abstract

An emulsifier-free process for the preparation of water expandable polymer beads, including: a) providing an emulsifier-free starting composition comprising styrene, b) prepolymerizing the starting composition to obtain a prepolymer composition, c) mixing an aqueous blowing agent with the prepolymer composition at an elevated temperature to obtain an inverse emulsion of water droplets in the prepolymer composition, wherein the aqueous blowing agent comprises water and a water soluble initiator dissolved in the water and the water droplets comprise spheres of a styrene polymer, wherein the water soluble initiator partly decomposes due to the elevated temperature leading to the formation of the inverse emulsion of water droplets in the prepolymer composition, d) suspending the inverse emulsion in an aqueous medium to yield an aqueous suspension of suspended droplets and e) polymerizing monomers in the droplets of the suspension obtained by step d) to obtain the water expandable polymer beads.

Claims

1. An emulsifier-free process for the preparation of water expandable polymer beads, which process comprises the steps of: a) providing an emulsifier-free starting composition comprising styrene, b) prepolymerizing the starting composition to obtain a prepolymer composition, c) mixing an aqueous blowing agent with the prepolymer composition at an elevated temperature to obtain an inverse emulsion of water droplets in the prepolymer composition, wherein the aqueous blowing agent comprises water and a water soluble initiator dissolved in the water and the water droplets comprise spheres of a styrene polymer, wherein the water soluble initiator partly decomposes due to the elevated temperature leading to the formation of the inverse emulsion of water droplets in the prepolymer composition, d) suspending the inverse emulsion in an aqueous medium to yield an aqueous suspension of suspended droplets and e) polymerizing monomers in the droplets of the suspension obtained by step d) to obtain the water expandable polymer beads.

2. The process of claim 1, wherein the water soluble initiator is a persulfate.

3. The process of claim 2, wherein the water soluble initiator is selected from the group consisting of sodium Na.sub.2SO.sub.5, KHSO.sub.5, K.sub.2S.sub.2O.sub.8, Na.sub.2S.sub.2O.sub.8 and (NH.sub.4).sub.2S.sub.2O.sub.8.

4. The process of claim 1, wherein the aqueous blowing agent further comprises a modifier-free nanoclay dispersed in the water.

5. The process according to claim 4, wherein the modifier-free nanoclay is an unmodified sodium montmorillonite nanoclay.

6. The process according to claim 4, wherein the amount of the nanoclay is 0.1-10 wt % of the total weight of the monomers in the starting composition.

7. The process of claim 1, wherein the aqueous blowing agent further comprises a water soluble polar comonomer containing a carbon-to-carbon double bond.

8. The process of claim 7, wherein the water soluble polar comonomer is selected from the group consisting of (meth)acrylic acid, styrene sulfonate, vinyl benzene boronic acid and salts thereof.

9. The process claim 1, wherein the starting composition further comprises a polyphenylene ether resin.

10. The process according to claim 1, wherein step b) comprises heating the starting composition at a temperature of 85-91 C. for a period of 30-120 minutes.

11. The process according to claim 1, wherein step c) comprises stirring the mixture at a temperature of 85-95 C.

12. The process according to claim 1, wherein step e) comprises heating the suspension obtained by step d) at a temperature of 90-135 C. for a period of 180-300 minutes.

13. Water expandable polymer beads obtained by the process according to claim 1.

14. Expanded polymer beads obtained by expanding the water expandable polymer beads according to claim 13.

15. The process according to claim 4, wherein: the amount of the nanoclay is 0.1-5 wt % of the total weight of the monomers in the starting composition, step b) comprises heating the starting composition for a period of 70-90 minutes, and step e) comprises heating the suspension obtained by step d) for a period of from 200-280 minutes.

16. The process according to claim 1, wherein: the water soluble initiator is a persulfate, and the aqueous blowing agent further comprises a modifier-free nanoclay dispersed in the water, and a water soluble polar comonomer containing a carbon-to-carbon double bond.

17. The process according to claim 1, wherein: the starting composition further comprises a polyphenylene ether resin, the nanoclay is an unmodified sodium montmorillonite nanoclay, the amount of the nanoclay is 0.1-10 wt % of of the total weight of the monomers in the starting composition.

18. The process according to claim 17, wherein the water soluble initiator is selected from the group consisting of sodium Na.sub.2SO.sub.5, KHSO.sub.5, K.sub.2S.sub.2O.sub.8, Na.sub.2S.sub.2O.sub.8 and (NH.sub.4).sub.2S.sub.2O.sub.8, and the water soluble polar comonomer is selected from the group consisting of (meth)acrylic acid, styrene sulfonate, vinyl benzene boronic acid and salts thereof.

19. Water expandable polymer beads obtained by the process according to claim 16.

20. Expanded polymer beads obtained by expanding the water expandable polymer beads according to claim 19.

Description

EXAMPLES

(1) Materials

(2) The monomers styrene, 4-styrenesulfonic acid sodium salt hydrate and acrylic acid, the initiators potassium persulfate, tert-butylperoxybenzoate and dibenzoyl peroxide (DBPO, 75% purity), and the PGV nanoclay used as water carrier were obtained from Aldrich and used as received.

(3) A dispersion of nanoclay in water (62.5 g/L) was prepared by mixing 40 g of PGV nanoclay in 640 mL demineralized water. Exfoliation of the nanoclay was effected according to the procedure described in WO2013/029757A1.

Example 1: WEPS Containing PS/AA Latex

(4) Preparation of the Blowing Agent Medium:

(5) 72.3 g of a dispersion of PGV nanoclay in water (62.5 g/L) was diluted with water (38.5 g) containing potassium persulfate (PPS) (0.20 g, 0.74 mmol). Acrylic acid (AA) (1.20 g, 16.7 mmol) was added and the nanoclay/water/acrylic acid mixture was homogenized.

(6) Preparation of Prepolymer:

(7) In a double-walled glass reactor (2.5 L), polyphenylene ether (PPE) (SABIC Noryl 855A, 100 g) was dissolved in styrene (850 g) at 65 C. A solution of dibenzoylperoxide (3.17 g, 13.1 mmol) and t-butylperoxybenzoate (0.9 g, 4.6 mmol) in styrene (50 g) was added to the PPE solution. The solution temperature was raised to 90 C. while stirring mechanically at 300 rpm. When the torque exerted on the stirrer by the prepolymer reached 2.8 Ncm, the stirring rate was increased to 600 rpm and the blowing agent medium was added in the course of 10 min and an emulsion was obtained. The temperature of the emulsion was allowed to come back to 90 C. while still stirring at 600 rpm.

(8) Suspension Polymerization:

(9) When the torque readout in the prepolymerization reached 7.0 Ncm, the prepolymer was added to a stirred (400 rpm) suspension of tricalciumphosphate (Ca.sub.3(PO.sub.4).sub.2, (14 g, 45 mmol) in water (2.5 kg) in which potassium persulfate (11 mg, 41 mol) was dissolved in a 6.4 L steel autoclave. The suspension polymerization was performed following the temperature program below:

(10) TABLE-US-00001 t(min) 90 60 60 15 15 T(C.) 90 90 .fwdarw. 120 120 .fwdarw. 130 130

(11) After cooling to room temperature, the beads were collected by filtration over a polyester sieve cloth (mesh 80 m) and thoroughly washed with water. Excess water was removed by centrifugation of the beads in the sieve cloth. Further drying of the bead surface was effected by passing a stream of dry nitrogen gas at 30 C. over the beads for 1 hr. The beads were subsequently sieved into 4 cuts (1.7-1.18, 1.18-0.80, 0.80-0.60 and 0.60-0.40 mm) and stored in air-tight containers.

(12) Characterization of WEPS Beads:

(13) The water content of the beads was determined by Karl-Fischer titration using a Metrohm 831 KF Coulometer in combination with a Metrohm Thermoprep 832 oven at 160 C.

(14) Molecular weight averages (Mw, Mn) Molecular weight distribution (MWD) and its broadness, described by polydispersity index, PDI=Mw/Mn (wherein Mn is the number average molecular weight and Mw is the weight average molecular weight) were determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99.

(15) Glass transition temperatures (T.sub.g) were measured on a Thermal Analysis DSC Q1000. Prior to DSC measurements, the entrapped water was removed from the beads by drying in a vacuum oven for 24 hrs. The temperature was varied between 25 and 140 C. employing heating and cooling rates of 10 cc/min. Only the second run was used for evaluation so as to erase any thermal history.

(16) SEM micrographs were obtained using a JEOL JSM-5600 SEM apparatus. Sliced beads were sputtered with gold.

(17) Expansion of WEPS Beads:

(18) The 1.18-0.80 mm sieve cut was used in expansion experiments. Approximately 0.5-1.0 g of beads were placed in a spherical metal wire basket ( 32 mm). The basket was immersed in Dow Corning DC200 silicon oil at 140 C. for 5-10 s. The basket was removed from the oil bath and immediately chilled in a bath of liquid nitrogen. Excess oil was subsequently removed by washing with pentane. This procedure was repeated until 30 mL of foamed material was obtained. The foamed beads were dried in open air and the bulk density .sub.B was determined gravimetrically on 30 mL of foamed beads.

Example 2: WEPS Containing PS/PSSO3Na Latex

(19) Preparation of the Blowing Agent Medium:

(20) 72.3 g of a dispersion of PGV nanoclay in water (62.5 g/L) was diluted with water (38.5 g) containing potassium persulfate (0.20 g, 0.74 mmol). Sodium 4-vinylbenzene sulfonate (StySO.sub.3Na) (3.4 g, 16.7 mmol) was added and the blowing agent medium was homogenized.

(21) Preparation of prepolymer and subsequent suspension polymerization were carried out according to the procedure given in Example 1. Expansion of the WEPS beads was effected as described for Example 1.

Example 3: WEPS Containing PS Latex (SAB1106)

(22) Preparation of the Blowing Agent Medium:

(23) Potassium persulfate (0.20 g, 0.74 mmol) was added to a dispersion of PGV nanoclay in water (90 g, 62.5 g/L) and the mixture was homogenized.

(24) Preparation of prepolymer and subsequent suspension polymerization were carried out according to the procedure given in Example 1.

Example 4: WEPS Containing PS/AA Latex without Nanoclay

(25) Preparation of the Blowing Agent Medium:

(26) Potassium persulfate (0.20 g, 0.74 mmol) was dissolved in water (90 g). Acrylic acid (1.80 g, 25.0 mmol) was added and the mixture was homogenized.

(27) Preparation of prepolymer and subsequent suspension polymerization were carried out according to the procedure given in Example 1.

Example 5: WEPS Containing PS/AA Latex without PPE, but with Nanoclay

(28) Preparation of the Blowing Agent Medium:

(29) Acrylic acid (1.17 g, 16.2 mmol) was added to 90 g of a dispersion of PGV nanoclay in water (62.5 g/L). Potassium persulfate (0.22 g, 0.74 mmol) was added and the mixture was homogenized.

(30) Preparation of Prepolymer:

(31) In a double-walled glass reactor (2.5 L), a solution of dibenzoylperoxide (5.3 g, 21.9 mmol) and t-butylperoxybenzoate (1.0 g, 5.2 mmol) in styrene (1000 g) was heated at 90 C. while stirring mechanically at 300 rpm. When the torque exerted on the stirrer by the prepolymer reached 2.7 Ncm, the stirring rate was increased to 600 rpm and the blowing agent medium was added in the course of 10 min and an emulsion was obtained. The temperature of the emulsion was allowed to come back to 90 C. while still stirring at 600 rpm.

(32) The suspension polymerization was carried out according to the procedure given in Example 1.

Example 6: WEPS Containing PS/AA Latex without PPE and without Nanoclay

(33) Preparation of the Blowing Agent Medium:

(34) Acrylic acid (2.0 g, 27.8 mmol) was dissolved in water (90 g), containing potassium persulfate (0.22 g, 0.81 mmol).

(35) Preparation of prepolymer and subsequent suspension polymerization were carried out according to the procedure given in Example 1. Expansion of the WEPS beads was effected as described for Example 1.

(36) Preparation of the Blowing Agent Medium:

(37) The blowing agent medium consisted of a dispersion of PGV nanoclay in water (111 g, 62.5 g/L).

(38) Preparation of prepolymer and subsequent suspension polymerization were carried out according to the procedure given in Example 1.

(39) Polymer properties of the WEPS beads are collected in Table 1.

(40) TABLE-US-00002 TABLE 1 Selected polymer properties for WEPS beads. Polar Mw T.sub.g Example PPE clay PPS Monomer kg/mol PDI C. Ex 1 + + + AA 250 5.3 106 Ex 2 + + + StySO.sub.3Na 273 3.9 113 Ex 3 + + + 190 4.2 112 Ex 4 + + AA 162 3.9 109 Ex 5 + + + AA 145 2.8 97 Ex 6 + + AA 193 4.1 97 Comp. + + 214 4.5 111 Ex A
Expansion properties of WEPS beads are collected in Table 2.

(41) TABLE-US-00003 TABLE 2 Water content of unfoamed WEPS beads and bulk densities of expanded WEPS beads. Polar d.sub.max [H.sub.2O ] .sub.B Example PPE clay PPS Mon m wt % kg/m.sup.3 Ex 1 + + + AA 20 10.1 54 Ex 2 + + + StySO.sub.3Na 30 12.6 57 Ex 3 + + + 45 8.2 77 Ex 4 + + AA 20 4.1 81 Ex 5 + + AA 45 8.8 102 Ex 6 + AA 50 5.3 95 Comp. + + 75 10.8 212 Ex A

(42) Comparison of the results according to comparative experiment A and the results according to example 3 shows the effect of the PPS in the blowing agent. By application of the preparation process according to the invention according to example 3 (use of PPS as initiator), the diameter of the water droplets in the WEPS beads is lower compared to the process in which no initiator was used in the blowing agent. This leads to better expandable WEPS beads; the bulk density of the expanded beads is lowered from 212 kg/m.sup.3 to 77 kg/m.sup.3.

(43) Further, the effects of the presence of PPE in the starting composition and the presence of nanoclay and polar comonomer in the blowing agent can be seen by comparison of examples 1 and 4-6.

(44) In example 6, the blowing agent comprises a polar comonomer acrylic acid. By the addition of the PPE according to example 4 in comparison with example 6, the diameter of the water droplets in the WEPS beads is lowered considerably. By the addition of the nanoclay according to example 5 in comparison with example 6, the amount of water in the non-expanded WEPS is increased. When both nanoclay and PPE are added according to example 1, the diameter of the water droplets in the WEPS beads is further reduced and the amount of water in the non-expanded WEPS beads is further increased. This together leads to better expandable WEPS beads, with a low bulk density of 54 kg/m.sup.3. Ex 2 shows that similar effects can be obtained by the use of a different comonomer.

(45) Morphology of WEPS Beads Before and after Foaming

(46) The morphology of unexpanded and expanded WEPS beads was studied by scanning electron microscopy (SEM).

(47) FIG. 1a shows a SEM micrograph of a WEPS bead prepared according to example 1 of the present invention (PS/AA-latex). The cross-section shows a distribution of holes with diameter d<20 m. FIG. 1b shows a close-up of one of the holes completely filled with PS latex particles with a diameter d<400 nm.

(48) FIG. 2 shows a SEM micrograph of a WEPS bead, prepared according to Example 1 and subjected to the foaming procedure as described above.

(49) FIG. 3a shows a SEM micrograph of a WEPS bead prepared according to Example 2 of the present invention (PS/PSSO.sub.3Na AA-latex). The cross-section shows a distribution of holes with diameter d<30 m. FIG. 3b shows a close-up of one of the holes filled with latex particles.

(50) FIG. 4 shows a SEM micrograph of a WEPS bead, prepared according to Example 2 and subjected to the foaming procedure as described above.

(51) FIG. 5a shows a SEM mictograph of a WEPS bead prepared according to Example 3 of the present invention (PS-latex). The cross-section shows a distribution of holes with diameter d<45 m. FIG. 5b shows a close-up of one of the holes filled with PS latex particles.

(52) FIG. 6 shows a SEM micrograph of a WEPS bead, prepared according to Example 3 and subjected to the foaming procedure as described above.

(53) FIG. 7a shows a SEM mictograph of a WEPS bead prepared according to Example 4 of the present invention (PS/AA-latex, no nanoclay). The cross-section shows a distribution of holes with diameter d<20 m. FIG. 7b shows a close-up of one of the holes filled with latex particles.

(54) FIG. 8 shows a SEM micrograph of a WEPS bead, prepared according to Example 4 and subjected to the foaming procedure as described above.

(55) FIG. 9a shows a SEM mictograph of a WEPS bead prepared according to Example 5 of the present invention (PS/AA-latex, no PPE). The cross-section shows a distribution of holes with diameter d<45 m. FIG. 9b shows a close-up of three of the larger holes filled with latex particles.

(56) FIG. 10 shows a SEM micrograph of a WEPS bead, prepared according to Example 5 and subjected to the foaming procedure as described above.

(57) FIG. 11a shows a SEM mictograph of a WEPS bead prepared according to Example 6 of the present invention (PS/AA-latex, no nanoclay, no PPE). The cross-section shows a distribution of holes with diameter d<50 m. FIG. 11b shows a close-up of one of the holes partially filled with latex particles.

(58) FIG. 12 shows a SEM micrograph of a WEPS bead, prepared according to Example 6 and subjected to the foaming procedure as described above.

(59) FIG. 13a shows a SEM mictograph of a WEPS bead prepared according to Comparative Example A of the present invention (PS/PPE, no latex). The cross-section shows a distribution of holes with diameter d<75 m. FIG. 13b shows a close-up of one of the holes demonstrating the absence of latex.

(60) FIG. 14 shows a SEM micrograph of a WEPS bead, prepared according to Comparative Example A and subjected to the foaming procedure as described above.

(61) Cross-sections of unfoamed WEPS beads are shown in FIGS. 1, 3, 5, 7, 9, 11 and 13. In all cases, holes can be observed on the surface of the cross-section. These holes result from water droplets entrapped in the polymer matrix which leave holes upon evaporation of the water during cross-sectioning. For good expansion it is beneficial to have many droplets with small diameters (d), evenly distributed throughout the bead. In the case of latex-recipes, the holes are partially or completely filled with latex particles.