Composite and methods of production

Abstract

Method of making a composite material by paste polymerization, by forming an emulsion of at least one polymerizable monomer in an aqueous material, polymerizing the emulsion to provide a latex containing particles of polymer, in which the polymer has a glass transition temperature above 65° C., adding nanoparticles to the latex, the nanoparticles having at least one dimension in the range 0.5 to 200 nm, and spray-drying the latex. The at least one polymerizable monomer contains vinyl chloride.

Claims

1. A method of making a composite material by paste polymerisation comprising the steps of: a) forming an emulsion of at least one polymerisable monomer in an aqueous material, b) polymerising the emulsion to provide a latex comprising particles of polymer, wherein said polymer has a glass transition temperature above 65° C., and further wherein said particles have a volume average particle size as measured by light scattering of from 0.2 to 5 microns, c) adding nanoparticles to the latex, said nanoparticles having at least one dimension in the range 0.5 to 200 nm, wherein the nanoparticles are added in an amount of 0.5-25 wt % based on the weight of the polymer particles before addition of the nanoparticles, and d) spray-drying the latex, wherein the at least one polymerisable monomer comprises vinyl chloride.

2. A method as claimed in claim 1 comprising, after step (d), a further step (e) of forming the dried composite material into either a sheet or plastisol.

3. A method as claimed in claim 2 wherein the glass transition temperature is above 66° C.

4. A method as claimed in claim 1 wherein the glass transition temperature is above 66° C.

5. A method as claimed in claim 1 wherein the polymer formed in step (b) is a PVC homopolymer.

6. A method as claimed in claim 1 wherein the nanoparticles are added as an aqueous dispersion.

7. A method as claimed in claim 1 wherein the nanoparticles comprise silica.

8. A method as claimed in claim 1 wherein the spray-dried particles of the composite material have an average particle size in the range 10-63 microns.

9. A method as claimed in claim 2 wherein the polymer formed in step (b) is a homopolymer.

10. A method as claimed in claim 2 wherein the nanoparticles are added as an aqueous dispersion.

11. A method as claimed in claim 2 wherein the nanoparticles comprise silica.

12. A method as claimed in claim 2 wherein the spray-dried particles of the composite material have an average particle size in the range 10-63 microns.

13. A method as claimed in claim 3 wherein the glass transition temperature is at least 68° C.

14. A method as claimed in claim 13 wherein the glass transition temperature is at least 70° C.

15. A method as claimed in claim 4 wherein the glass transition temperature is at least 68° C.

16. A method as claimed in claim 15 wherein the glass transition temperature is at least 70° C.

17. A method as claimed in claim 16 wherein the glass transition temperature is at least 70-85° C.

18. A method as claimed in claim 8 wherein the spray-dried particles of the composite material have an average particle size in the range 15-40 microns.

19. A method as claimed in claim 12 wherein the spray-dried particles of the composite material have an average particle size in the range 15-40 microns.

Description

EXAMPLE 1

(1) Water, vinyl chloride monomer (VCM) and an initiator were charged into a reactor to produce a PVC latex in well-known fashion. Once the reaction has finished the latex is transferred to another vessel and 5% by weight Bindzil® 40/130 added with stirring to give a homogenous dispersion. Percentage by weight was calculated as percentage dry matter in the Bindzil relative to dry PVC in the mixture. Bindzil® is a colloidal nano silica dispersed in an aqueous media and made by AkzoNobel BV. The mixture was then spray dried to give a dry PVC powder.

(2) A portion of the powder was mixed with 5 phr stabiliser and 2 phr processing aid and processed on a two roll mill to produce sheets. The sheets were pressed at 160 C. A further portion of the powder was mixed with 80 phr diisononylisophthalate (DINP) plasticiser and 2.5 phr to produce a plastisol.

Comparative Example 1

(3) The same amount of water, VCM and initiator as set out in Example 1 were charged into a reactor along with 5% by weight Bindzil® 40/130 and the VCM allowed to polymerise under the same conditions as Example 1. When polymerisation was complete the mixture was spray dried in the same manner as in Example 1 to give a dry PVC powder. Sheets and plastisol were prepared in the same way as in Example 1.

Comparative Example 2

(4) The same amount of water. VCM and initiator as set out in Example 1 were charged into a reactor and allowed to react under the same conditions as in Example 1. When polymerisation was complete the mixture was spray dried under the same conditions as Example 1 to give a dry PVC powder. Sheets and plastisol were prepared in the same way as Example 1.

Comparative Example 3

(5) The same amount of water. VCM and initiator as set out in Example 1 were charged into a reactor and allowed to react under the same conditions as in Example 1. Once the reaction has finished the latex is transferred to another vessel and 5% by weight Bindzil® 40/130 added with stirring to give a homogenous dispersion. Percentage by weight was calculated as percentage dry matter in the Bindzil relative to dry PVC in the mixture. The latex was coagulated by freezing and the frozen latex was dried in a vacuum oven until a dry powder was formed. Sheets were prepared in the same way as Example 1.

(6) The physical properties of the sheets were measured and the results are shown in Table 1:

(7) TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 Example 1 Example 2 Example 3. Charpy Impact 18.9 9.96 7.65 13.90 (ISO179) kJ/m2 Standard 0.88 1.36 0.68 1.47 Deviation Tensile strength 51.4 52.8 57.4 52.3 (MPa) Standard 0.47 0.47 0.45 0.68 Deviation Elastic Modulus 2933 3033 3150 3052 (MPa) Standard 88 89 201 46 Deviation

(8) It will be apparent that the Charpy Impact strength of the composition of the invention is very significantly greater than either similar material where the nanoparticles are present when the VCM monomer is polymerised (Comparative Example 1) and when nanoparticles are not present (Comparative Example 2). Further, it will be apparent that the Charpy Impact strength of the composition of the invention is significantly greater than similar material where the latex is not dried by spray-drying but by coagulation (Comparative Example 3). The tensile strength and elastic modulus remain broadly unchanged.

(9) The viscosity of the plastisol was measured with a Brookfield™ viscometer after 2 h and the results are shown in Table 2.

(10) TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 1 Example 2 Brookfield 2.5 rpm 336 728 197 Brookfield 20 rpm 64.2 >100 42.8 Brookfield 100 rpm 19.5 >50 14.9

(11) It will be apparent from Table 2 that the plastisol of the invention has reduced viscosity compared with a nanoparticle containing material made in another way.

EXAMPLE 3

(12) A latex was made as described in Example 1. Elkem NanoSilica® 999 (available from Elkem AS) was dispersed in water to give a 50 wt % dispersion. This dispersion was added to the latex to give 10 wt % silica content in the mixture. Percentage by weight was calculated as percentage dry matter in the Nanosilica® 999 dispersion relative to dry PVC in the mixture.

(13) The mixture was then spray dried to give dry PVC particles in the same manners as described in connection with example 1. A portion of the powder was formed into a sheet as described in Example 1.

Comparative Example 4

(14) Dry PVC particles of Comparative Example 2 were blended with 10 phr Elkem Nanosilica® 999 5 phr stabiliser and 2 phr stabiliser and formed into sheets as described by reference to Example 1.

(15) The Charpy Impact Strength of the materials was measured and is shown in Table 3

(16) TABLE-US-00003 TABLE 3 Comparative Comparative Example 3 Example 2 Example 4 Charpy Impact 19.7 7.65 18.15 Strength (ISO 179) Standard Deviation 0.72 0.68 0.84

(17) It will be seen that the impact strength of the product of the invention is significantly (greater than 2 sigma) stronger than material in which nanoparticles had been introduced after latex drying and very significantly stronger than material which contains no nanoparticles.