**5. Conclusions**

Composites were also prepared by gently heating the epoxy resin to reduce viscosity, blending the cellulose using a stir plate, and use of a sonication bath to help separate some of the slower dispersing particles. Epoxies containing 2 % MePh3P-CNC were visibly transparent, and the microscopic images (not shown) suggest similar levels of crystal separation and dispersion

The differences in particle size and surface energy of the crystals resulted in differences in the glass transition temperatures (cf **Figure 7**). The cellulose nanocrystals interacts strongly with the epoxy matrix, leading to a 5 °C increase in the glass transition temperature at 2 % NaCNC loading. This behavior is consistent with other studies incorporating cellulose nanofibers [43] or nanocrystals [44]. The addition of MePh3PCNC does not change the glass transition

the cellulose, reducing both crystal–crystal interactions (less aggregation), and cellulose– polymer interactions (lower Tg). The differences in Tg between the epoxies prepared using high

**Figure 7.** Glass transition temperatures of epoxy-cellulose nanocrystal composites using DSC. Error bars represent 2σ.

The tensile properties of the epoxy composites are provided in **Table 2**. As expected, the incorporation of stiff crystals increased the modulus (E) of the epoxy composites. The addition of MePh3P-CNC had a greater effect than the addition of Na-CNC, likely due to the smaller size of aggregates and better dispersion in these composites. The peak tensile strength (σp) of

shear mixing and those using mechanical mixing were not statistically significant.

functionality lowers the surface energy of

throughout the epoxy.

210 Composites from Renewable and Sustainable Materials

temperature relative to neat epoxy. The MePh3P+

Epoxy composites were filled with lignocellulosic materials to improve their flammability and mechanical properties. Lignosulfonate was used as a condensed phase flame retardant. The lignosulfonate migrated during the curing process and resulted in delamination, reducing its effectiveness at maintaining a protective char layer during combustion. The lignosulfonate was successfully epoxidated and incorporated within the epoxy matrix. This reduced the migration and improved the fire performance of the composite. Cellulose nanocrystals were successfully incorporated in an epoxy composite without the aid of a solvent by modifying the crystals with a simple ion exchange process. This process minimized aggregation of cellulose without the use of nonaqueous solvents. The resulting composites were transparent, were stiffer, had a smaller loss in tensile strength, and absorbed less water than the composites with unmodified Na-CNC.
