Polyurethane composites produced by a vacuum infusion process

1. A process for producing a fiber-reinforced polyurethane composite article by vacuum infusion molding, comprising:

(a) degassing components comprising an isocyanate component and an isocyanate-reactive component, wherein:

(1) the isocyanate component has a viscosity at 25° C. of from about 20 to about 300 mPas and comprises a diisocyanate or a polyisocyanate, and

(2) the isocyanate-reactive component comprises:

(i) one or more polyols having a viscosity at 25° C. of from 20 to 850 mPas, and an OH number of from about 200 to about 600,

(ii) up to about 6% by weight, based on total isocyanate-reactive component, of a flow additive, and

(iii) from about 2 to about 6% by weight, based on total isocyanate-reactive component, of a drying agent,

with the sum of the weight percents for all of the components of the isocyanate-reactive component being equal to 100% by weight;

(b) combining the de-gassed components (1) and (2) to obtain a polyurethane-forming reaction mixture having a viscosity at 25° C. of less than 600 mPa·s for at least 30 minutes, a gel time at ambient temperature of greater than 60 minutes and a water content of less than 0.06% by weight, based on total system weight, wherein components (1) and (2) are combined in amounts such that the NCO Index is from 99 to 110 to form a polyurethane having sufficient green strength to be de-molded at ambient temperature in no greater than 6 hours;

(c) placing a fibrous reinforcing material in a vacuum chamber arranged to form a wind turbine blade;

(d) drawing down the pressure within the vacuum chamber to thereby push the reaction mixture into the vacuum chamber and into the fibrous reinforcing material; and

(e) curing the reaction mixture to form a composite of the fibrous reinforcing material infused with the cured reaction mixture that is in the form of a wind turbine blade.

2. The process of claim 1 in which the reaction mixture has a viscosity at 25° C. of less than 400 mPas.

3. The process of claim 1 in which the reaction mixture has a viscosity at 25° C. of from 250 to 300 mPas.

4. The process of claim 1 in which (2)(i) is a polyether polyol.

5. The process of claim 1 in which (2)(i) includes two or more polyether polyols.

6. The process of claim 1 in which the reaction mixture has a gel time of greater than 180 minutes.

7. The process of claim 1 in which the isocyanate component has a viscosity at 25° C. of less than 100 mPa·s.

8. The process of claim 1 in which the isocyanate component comprises diphenylmethane diisocyanate (MDI) or polymeric MDI.

9. The process of claim 1 in which (2)(i) has a viscosity at 25° C. of from 600 to 700 mPa·s.

10. The process of claim 1 in which (2)(i) includes a polyol having a viscosity at 25° C. of from 50 to 75 mPa·s.

11. The process of claim 1 in which the isocyanate-reactive component has an average functionality of from 2 to 3.

12. The process of claim 1 in which components (1) and (2) are reacted in amounts such that the NCO Index is approximately 1.02.

13. The process of claim 1 in which the fibrous reinforcing material comprises glass fibers, carbon fibers, aramid fibers and/or basalt fibers.

14. The process of claim 1 , wherein the fiber-reinforced polyurethane composite article consists of fibrous reinforcing material infused with the cured reaction mixture.

15. The process of claim 1 , wherein the composite comprises 30 to 80% by weight of reinforcing material, based on the total weight of the final composite.

16. The process of claim 15 , wherein the composite comprises 50 to 72% by weight of reinforcing material, based on the total weight of the final composite.