Improvement in the elasticity and toughness of polymeric materials is an important issue in the fabrication of polymeric materials. However, solving this issue is challenging because of the trade-off between toughness and elasticity. Herein, citric acid-modified cellulose (CAC) was introduced as a filler into movable cross-linked polymeric materials, in which cyclic molecules move along the polymer chain. The resulting CAC/polymer composite materials contained both reversible and movable cross-links. The reversible cross-links were hydrogen bonds formed between the carboxyl group of acrylic acid units (AA; in the polymer chain) and the CAC filler. The movable cross-links were formed by a cyclic molecule along the polymer chain. This combination of reversible and movable cross-links resulted in the high toughness of the composite materials against an applied stress. The CAC/polymer composite materials with 3 wt % CAC increased the Young’s modulus by 1.6 times and maintained the toughness compared to the original elastomer without the CAC. The CAC/polymer composite materials without CAC or the AA unit did not show this increase. Dynamic viscoelasticity measurements revealed the relationship between the relaxation modes and the toughness of the CAC/polymer composite materials. Upon combining the appropriate unit ratio of movable and reversible cross-links, the CAC/polymer composite materials exhibited the highest Young’s modulus and toughness. The design of the CAC/polymer composite materials improved the toughness with a high Young’s modulus.

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