The present work investigates the combined efect of the addition of graphite nanoplatelets (xGNPs) to polyurethane copolymer (PUC) and thermal treatment was employed. The PUC reinforced by xGNP were synthesized by in-situ polymerisation,
which leads to an efective performance of the PUC/xGNP system. Meanwhile, X-ray difraction (XRD) and Raman spectroscopy tests displayed the inter-spacing planar quality of xGNP nanofllers. The thermal stability of PUC was seen to increase
with addition of xGNP. Additionally, the dynamic storage modulus (E?) showed better performance after thermal treatment
than in the untreated samples. However, a relationship between the microphase-separated morphology of PUC induced by
thermal treatment and the addition of xGNP has been observed. Consequently, the crystallinity percentage increased after
thermal treatment @ 80 ?C for 4 days, presuming a re-ordering of amorphous hard segments during the heating in a packed
microphase conformation. On the other hand, better dispersion and interaction of xGNP can play a crucial role in enhancing
the thermal and mechanical properties, and thus a signifcant reinforcement for PUC. The tensile properties such as modulus
and tensile strength showed signifcant enhancement with xGNP incorporation, while the elongation steeply dropped. On
the contrary, a deterioration in modulus and tensile strength resulted from thermal treatment, likely due to the restacking of
xGNP during segmental movement and thus increasing the amorphous phase rather than the crystalline phase. A modifed
Halpin–Tsai model was utilised to predict the mismatch between the empirical and theoretical results. Consequently, the
fndings displayed the divergence of the nanocomposite modulus of PUC with greater amounts of xGNP nanofllers.