Process for producing polymethyl methacrylate rigid foams as core materials in rotor blades of wind power plants and in boatbuilding

Abstract

PMMA-based rigid foams can be used as the core material of sandwich components in rotor blades of wind power plants and in boatbuilding.

Claims

1: A process for producing polymethyl methacrylate-based rigid foams in sandwich components for use in wind power plants and boatbuilding, the process comprising: foaming a blowing agent-laden polymer composition to afford a polymethyl methacrylate-based rigid foam having an average pore size in the range from 50 to 300 μm measured according to ASTM D3576, wherein the polymethyl methacrylate-based rigid foam has a glass transition temperature Tg above 110° C. determined by DMTA measurement according to ISO 6721-7 standard.

2: The process for producing polymethyl methacrylate-based rigid foams according to claim 1, wherein a resin absorption of the polymethyl methacrylate-based rigid foam is between 0.01 and 0.03 g/cm.sup.2 measured according to VARI.

3: The process for producing polymethyl methacrylate-based rigid foams according to claim 1, further comprising: curing of a resin during production of the sandwich components at a temperature greater than 110° C. by heating or irradiating in a mould.

4: The process for producing polymethyl methacrylate-based rigid foams according to claim 3, wherein the curing of the resin is effected in an electrically heatable mould.

5: The process for producing polymethyl methacrylate-based rigid foams according to claim 3, wherein the curing of the resin is performed by means of IR radiation.

6: The process for producing polymethyl methacrylate-based rigid foams according to claim 1, wherein the polymethyl methacrylate-based rigid foam has a density of 30-500 kg/m.sup.3 measured according to DIN EN ISO 1183.

7: A polymethyl methacrylate-based rigid foam in a sandwich component produced according to the process of claim 1, wherein the polymethyl methacrylate-based rigid foam is employed as a core material in rotor blades of wind power plants or in boatbuilding, in lightweight construction, as a packaging material, as an energy absorber in crash elements, in architectural building elements, as a diffuser in lighting applications, in furniture construction, in vehicle construction, in the aerospace industry, or in model building.

Description

EXEMPLARY EMBODIMENTS

[0047] Resin Absorption

[0048] Materials Used:

[0049] PVC foam: Airex C70.55 from 3A Composites, Steinhausen ZG (Switzerland)

[0050] PET foam: Airex T10.100 from 3A Composites, Steinhausen ZG (Switzerland)

[0051] PMMA foam: ROHACRYL55 from Evonik Resource Efficiency GmbH, Germany

[0052] The resin absorption of the core materials must be experimentally determined by VARI (vacuum assisted resin infusion). Minimum dimensions for the specimen sheets of 300×300 mm are specified.

[0053] Before infusion the specimen dimensions and specimen weights must be adjusted to a measurement accuracy of ±0.01 mm and ±0.01 g to determine specimen density and basis weight. Since the viscosity of the resin is strongly dependent on temperature, the test setup is heated to 30° C. to ensure constant conditions. The airtightness of the test setup was tested by a vacuum test, wherein resin inlets and outlets were clamped off and vacuum loss was checked after 30 min.

[0054] In addition, the resin components should be degassed. This is carried out by evacuating the resin and the hardener under vacuum at −0.8 bar and 40° C. for 60 min. Before mixing, both components must be cooled to room temperature in order that the reaction may be commenced in controlled fashion. This was followed by a second deaeration of the resin system at −0.8 bar and 40° C. for 10 min. Infusion can be commenced once the vacuum test of the test setup is complete. The vacuum should be maintained until the resin has solidified. After termination of the infusion, the resin system should cure at 30° C. for at least 18 hours.

[0055] Finally, the edges were squared and the peel plies were removed. The difference between the basis weight of the dry foam sheet and the injected foam sheet gives the resin absorption.

[0056] The obtained values for resin absorption are summarized in the following table:

TABLE-US-00001 Resin absorption Foam (g/cm.sup.2) PMMA foam 0.0196 PET foam 0.0591 PVC foam 0.0370

[0057] Outer Layer Adhesion

[0058] According to the standard drum peel test (DIN 53295), a sandwich sheet having a projection of the outer layer was clamped into the known test setup. With the aid of a gripper, the outer layer was gripped by its projection and peeled from the core material at a constant apparatus speed. The force required therefor is plotted. This provides information about outer layer adhesion.

[0059] The tests performed resulted in failure of the foam material. The fact that cohesive failure rather than adhesive failure (separation of foam core and outer layer in the adhesive layer (resin layer)) is observed is indicative of good outer layer adhesion.

[0060] This demonstrates sufficient outer layer adhesion to the PMMA foam core.

[0061] Outer layer adhesion is also measured in another test method.

[0062] The flatwise test (ASTM C297) is performed using 50×50 mm test specimens. The test specimen consists of a foam core, a resin layer and an outer layer on the top surface and the bottom surface. The test specimen is clamped into the tensile apparatus. The upper holder is pulled at a constant tensile test speed.

[0063] Pulling was continued until the failure of the foam core in the performed tests. No detachment of the outer layer from the core material at the resin layer was detected.

[0064] This demonstrates sufficient outer layer adhesion.

[0065] Measurement of Glass Transition Temperature to Estimate Heat Distortion Temperature

[0066] Tg values were determined via DMTA measurements according to the standard ISO 6721-7. The following values were determined:

TABLE-US-00002 Foam T.sub.g (° C.) PMMA foam 145 PET foam 80 PVC foam 80

[0067] Curing at Elevated Temperature

[0068] The foam core provided with the outer layers is injected with an epoxy resin. The material is heated to 110° C. in the sealed mould. Crosslinking is accelerated by the elevated temperature.

[0069] Relatively short cycle times were determined. In comparative tests performed at room temperature the curing time was more than 24 h. At a temperature of 110° C. the curing process was able to be shortened to 20 min.