Recyclable sandwich structure composites

A composite structure comprising two skin sheets, and a core member arranged between the two skin sheets, wherein,

• the skin sheet comprises a reinforcing fibre impregnated with a recyclable epoxy resin;
• and
• the core member comprises the recyclable epoxy resin, a reinforcing component, and a foaming agent,
• the recyclable epoxy resin comprising at least one epoxy resin component and a recyclable curing agent wherein the recyclable curing agent is selected from a group consisting of a compound of Formula (I):
• wherein:
• if m is 2, then n is 2;
• if m is 1, then n is 3;
• or
• if m is 0, then n is 4;
• each R1 is independently hydrogen, alkyl, cycloalkyl, heterocycle, heterocycloalkyl, alkenyl, cycloalkenyl, aryl, heteroaryl, alkoxyalkyl, or alkynyl;
• each A is independently alkyl, alkylene, alkenene, alkylene-hetero-alkylene, alkylene-heterocyclo-alkylene, carbonyl, thiocarbonyl, alkylene-oxy-alkylene, 1,4-alkyl substituted piperazine, aryl, or heteroaryl;
• each R2 is independently —NHR3, —SH, or heterocycloalkyl, wherein each R3 is independently hydrogen, alkyl, aminoalkyl, alkylaminoalkyl, cycloalkyl, heterocycle, alkenyl, aryl, or heteroaryl;
• or, every two —O-A-R2 groups, together with the carbon atom to which they are attached to, can independently form an dioxanyl ring with no less than 4 ring members and one or more of the ring carbon atom(s), other than the carbon atom to which the two —O-A-R2 groups are attached, are independently substituted with one or more independent amino group or aminoalkyl wherein each amino is independently a primary or secondary amino group;
• and
• a compound of Formula (II):
• wherein:
• q is 4, 3, 2, or 1;
• tis 0, 1, 2, or 3;
• the sum of q and t is 4;
• each occurrence of W is independently alkylene, cycloalkylene, heterocyclylene, alkenylene, alkynylene, cycloalkenylene, arylene, or heteroarylene;
• and
• each occurrence of R5 is independently hydrogen, alkyl, aminoalkyl, cycloalkyl, heterocyclyl, alkenyl, alkynyl, cycloalkenyl, aryl, heteroaryl or —ORc, wherein Rc is alkyl, cycloalkyl, heterocyclyl, alkenyl, alkynyl, cycloalkenyl, aryl or heteroaryl.