To provide a lignophenol derivative composite material which is easily decompositable.

The composite material has a lignin-based matrix containing at least one lignin-based polymer selected from among (a) a lignophenol derivative having the first 1,1-bis(aryl)propane unit formed by bonding the carbon atom ortho to the phenolic hydroxy group of a phenol derivative to the carbon atom at the C1 position of the arylpropane unit of lignin, (b) a second-order derivative obtained by subjecting lignophenol derivative (a) to one reaction selected from a hydroxy group protection treatment, an alkali treatment, and a crosslinking-group introduction reaction, (c) a higher-order derivative obtained by subjecting lignophenol derivative (a) to at least two reactions selected from among a hydroxy group protection treatment, an alkali treatment, and a crosslinking-group introduction reaction, (d) a crosslinked product obtained by subjecting the second-order derivative to a crosslinking group introduction reaction, and (e) a crosslinked product obtained by subjecting the high-order derivative to a crosslinking group introduction reaction. The lignin-based polymer is contained in an amount enough to decomposite the composite material by an alkali treatment.

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