Polypropylene composite material having melting point gradient structure, preparation method therefor and system and use thereof

A polypropylene composite material, comprising a plurality of polypropylene sheet layer unit groups that are sequentially stacked;

• each polypropylene sheet layer unit group comprises at least one same or different polypropylene sheet layer units, and each polypropylene sheet layer unit comprises a core layer Ai and outer layers Bi and B′i located on both sides of the core layer Ai, with a structure of BiAiB′i;
• the structure of the polypropylene composite material is group n, . . . group i, . . . group 2, group 1, group 2, . . . group i, . . . group n, from bottom to top, the total number of the stacked groups of the polypropylene sheet layer unit groups is 2n−1;
• i and n are both integers not less than 2, and i≤n;
• wherein, in the polypropylene sheet layer unit, the core layer Ai contains a polypropylene composition Ai, the outer layer Bi is the same as or different from the outer layer B′i, the outer layer Bi contains the polypropylene composition Bi, and the outer layer B′i contains the polypropylene composition B′i,
• the melting point of the polypropylene composition Ai is greater than the melting point of the polypropylene composition Bi and of the polypropylene composition B′i;
• the average value of the melting points of all outer layers in group i is greater than the average value of the melting points of all outer layers in group i−1.