Kit for producing composite semi-finished products comprising reversibly crosslinked polymer emulsions
The invention concerns specifically emulsion polymers which are intraparticulately crosslinked via a hetero-Diels-Alder (HDA) mechanism. The crosslinked polymers can then be wholly or partly decrosslinked by thermal processing, for example in the form of a composite matrix, via a retro-Diels-Alder or retro-hetero-Diels-Alder reaction and interparticulately recrosslinked on cooling. This makes it possible to prepare long shelf life prepregs for composites. But it is also possible to thus realize other materials that have thermoset properties at use temperature but thermoplastic processing properties at a higher temperature.
1. A process for producing a semi-finished composite product or a moulded part of the semi-finished composite product, the process comprising:
(I) optionally shaping a fibrous material,
(II) preparing an aqueous poly(meth)acrylate dispersion via emulsion polymerization of a monomer composition, wherein the monomer composition comprises monomers having:
a group copolymerizable with (meth)acrylates, and
a diene functionality,
(III) mixing the dispersion with a compound comprising two or more dienophilic double bonds to produce a second composition,
(IV) directly impregnating the fibrous material with the second composition and shaping into an uncured shaped composition, and
(V) curing the uncured shaped composition at a crosslinking temperature T 1 thereby obtaining the semi-finished composite product or the moulded part of the semi-finished composite product,
wherein the compound comprising two or more dienophilic double bonds comprises meta-xylylenebismaleimide.
2. The process according to claim 1 , further comprising:
(VI) heating the semi-finished composite product or the moulded part of the semi-finished composite product to a decrosslinking temperature T 2 to produce a decrosslinked product,
(VII) reshaping the decrosslinked product into a reshaped composition, and
(VIII) newly curing the reshaped composition at the crosslinking temperature T 1 .
3. The process according to claim 2 , wherein the crosslinking temperature T 1 in step (V), step (VIII), or both, is between 0 and 60° C.
4. The process according to claim 2 , wherein:
step (V), step (VIII), or both, are performed at room temperature,
at least 50% of crosslinks are redetached in step (VI) at the decrosslinking temperature T 2 via a retro-hetero-Diels-Alder reaction, and
the decrosslinking temperature T 2 is between 50 and 150° C. above the crosslinking temperature T 1 .
5. The process according to claim 1 , wherein:
the step (III) and the step (IV) are carried out at a temperature T 3 which is at least 40° C. above the crosslinking temperature T 1 , and
the step (V) is performed by cooling down to the crosslinking temperature T 1 .
6. The process according to claim 2 , wherein the steps (VI)-(VIII) are repeated.
7. The process according to claim 1 , wherein, after process step (IV), the uncured shaped composition is dried at a temperature T 2 in a step (IVa).
8. The process according to claim 2 , further comprising:
cutting, milling, polishing, painting, or coating the semi-finished composite product or the moulded part of the semi-finished composite product after step (V) or step (VIII) to form a shaped article in a process step (IX).
9. The process according to claim 2 , further comprising:
recycling the semi-finished composite product or the moulded part of the semi-finished composite product from step (V) or step (VIII) in a step (X) at a temperature T 4 ,
wherein said temperature T 4 is not less than the decrosslinking temperature T 2 .
10. A semi-finished composite product or a moulded part of the semi-finished composite product obtained by the process of claim 1 , wherein the semi-finished composite product is at least one selected from the group consisting of a boat- or shipbuilding product, an aerospace technology product, an automobile construction product, a two-wheeler product, a civil engineering product, a biomedical engineering product, a sports sector product, an electrical product, an electronics industry product and a power generation product.
11. A shaped article obtained from the process of claim 8 , which is at least one selected from the group consisting of a boat- or shipbuilding product, an aerospace technology product, an automobile construction product, a two-wheeler product, a civil engineering product, a biomedical engineering product, a sports sector product, an electrical product, an electronics industry product and a power generation product.
12. The process according to claim 8 , further comprising:
recycling the shaped article from step (IX) in step (X) at a temperature T 4 , wherein said temperature T 4 is not less than the decrosslinking temperature T 2 .