Effects of molecular structure on the sintering of ethylene/a-Olefin copolymers
The objective of this work is to determine the effects of the polymer molecular structure on the sintering process. An experimental study on polymer sintering has been conducted in conjunction with an extensive characterization of the resins used in this work. A combination of rheological, thermal, and spectroscopic techniques was found to be effective in determining the molecular characteristics of the resins. Sintering experiments were conducted under isothermal and non-isothermal conditions using both powder and cylindrical particles. It was found that the trends observed for the sintering of powder were consistent with the predictions of Newtonian sintering models. Sintering results obtained using cylindrical particles, however, showed significant differences not seen when using powder particles. These were attributed to the differences in the surface area between the two types of particles. It is speculated that the effect of material properties other than viscosity and elasticity are enhanced when cylindrical particles are used. It was shown that an ( increase in the molecular weight, which translates into higher viscosity values, has a negative impact on polymer sintering. It was also shown that as the comonomer content increases, the sintering rate decreases. The presence of more side branches in the polymer chain causes a reduction in the degree of crystallinity. The resulting amorphous regions represent an obstacle to self-diffusion that negatively impacts the sintering process. On the other hand, an increase in the comonomer content generally results in a decrease in the melting temperature and the heat of fusion, which favors the onset of sintering. For the resins used in this study, it was difficult to evaluate the effect of the molecular weight distribution, comonomer type, and comonomer distribution on the sintering process. Experimental evidence suggested that copolymers with a more homogeneous structure generally sinter faster than their heterogeneous counterparts. Nevertheless, the presence of some heterogeneities in the molecular structure, while maintaining a relatively narrow molecular weight distribution, seemed to favor the sintering process in a few cases, especially with experiments conducted under non-isothermal conditions.
Bibliography: p. 109-115
Guillen Castellanos, S. A. (2001). Effects of molecular structure on the sintering of ethylene/a-Olefin copolymers (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/1941