Transmission electron microscopy (TEM) was performed on a JEM-2100 electron microscope operation at an acceleration voltage of 200 kV to characterize the morphology and distribution of cellulose nanocrystals. Infrared spectra was recorded at room temperature on NICOLET is 10 Fourier transform infrared spectroscopy (FT-IR) to characterize the surface modification of CNCs. The samples were prepared by KBr pellet method. The resolution of the spectrometer is 4 cm−1, the wave number range is 400–4000 cm−1, and the samples were scanned 30 times. The chemical structure of CNCs modified with styrene was characterized with Bruker 400 M solid-state 13C NMR. Thermostability of CNCs and PMMA composites was analyzed by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The thermal degradation of CNCs and composites was analyzed using thermal analyzer TGA/SDTA851e under nitrogen flow. The samples were heated from 30 to 550 ◦C at a heating rate of 10 ◦C min−1. The glass transition temperature of PMMA composites was measured with a Pyris 1 DSC instrument. The samples were scanned from 30 to 200 ◦C at a heating rate of 10 ◦C min−1. X-ray diffraction (XRD) patterns of raw MCC, manufactured CNCs and modified CNCs was recorded on Bruker Siemens D8 X-ray diffractometer operated at 3 kW with Cu K radiation ( = 0.154 nm) in the range 2 = 3–60◦ with a step of 0.02◦. The homogeneity of PMMA composites was observed using scanning electron microscopy (SEM) su1510 device (Hitachi Zosen Corporation) at 30 kV. The mechanical properties of Nano composites were investigated through breaking strength and elongation at break. UV–vis spectrophotometer was utilized at wavelength from 400 to 800 nm to measure the transmittance of nanocomposite films. 3