Laser dilatometry

The unique laser dilatometer apparatus was designed in our laboratory to study the softening of polyolefins, which is an important property with respect to industrial gas-phase polyolefin production. Softened polymers have higher adhesion tendencies, which can result in the formation of large polymer agglomerates and subsequently in the shutdown of the whole production line. Softening is a change in the mechanical properties of a polymer at elevated temperatures and is connected with a decrease of the Young modulus, i.e., with a decrease of the resistance to mechanical deformations. This is utilized in our experimental device, which detects polymer softening by measuring the deformation of a polymer powder sample subjected to static pressure and elevated temperature. The static pressure is exerted by a metal piston. The results are presented in the form of softening curves, where the dependency of the piston position on temperature is depicted (see Figures 2 and 3).


Figure 1. Schematic depiction of the laser dilatometer apparatus.


Polymer properties and penetrant sorption influence the softening behavior. From the polymer properties, we study the effects of polymer crystallinity and molecular weight. The effects of sorption are studied for a broad range of penetrants, including inert gases (nitrogen), monomers (ethylene, propene), co-monomers and diluents (hexene, butene or hexane). The effects of sorption are very important with respect to industrial applications, as the polymer is sorbed with penetrants in the relevant processes.

Figure 2. Effect of various penetrants on the softening of polyethylene.

Figure 3. Effect of polyethylene crystallinity (wt. fraction) on the softening behavior.