Numerous field and laboratory studies conclusively demonstrate that Vitrolite ® modifies polymer melt rheology, more specifically, lowers the viscosity in stress and strain rates typical of polymer finishing environments. Commonly asked questions are whether Vitrolite ® modifies polymeric liquid viscosity by altering the composition of the polymer or by nucleation and crystallization of semi-crystalline polymers. Several laboratory studies have shown that Vitrolite ® does not alter the composition of the polymer, nor does it affect the crystallization of semicrystalline polymers.
Four principal lines of evidence indicate that Vitrolite ® does not affect the composition of the polymer. These tests, covering a broad range of thermoplastics, may be categorized as those studying molecular size and structural effects, chemical composition and integrity, crystallization, and physical properties.
1. MOLECULAR SIZE AND STRUCTURE
Molecular size and structural effects were studied by extruding Vitrolite ® in a polycarbonate with narrow molecular weight distribution, up to a 5% level. Gel permeation chromatography was used to study the molecular chain characteristics of the extruded polymer with Vitrolite ®, and the results were compared with those for virgin polycarbonate and polycarbonate extruded without any Vitrolite ®. From Table 1 it is seen that the number average molecular weight (MN) and the weight average molecular weight (MW) of polycarbonate with Vitrolite ® are indistinguishable from that of polycarbonate as is. This implies that the molecular architecture and chain length of the polymer are not changed by processing with Vitrolite ® any more than that during typical processing of polycarbonate as is.
2. CHEMICAL NATURE OF POLYMER AND POLYMER DEGRADATION
Fourier Transform Infra-Red Spectroscopy was used as a means of chemical analysis to study the effect of Vitrolite ® on the Polystyrene. Figure 1 shows the trace of polystyrene as is (upper trace) and of polystyrene with 0.5% of Vitrolite ® (lower trace). The traces are identical, implying that no new molecular species indicative of polymer degradation have been created, when Vitrolite ® is added to the polymer.
Nuclear Magnetic Resonance Spectroscopy (NMR) was used to compare linear low density polyethylene (LLDPE) in pure form, and that extracted from a 50-50 concentrate with Vitrolite ®. The 50-50 concentrate of LLDPE was produced by extrusion. The NMR spectra of LLDPE as is and extracted LLDPE shown in Figure 2 are identical. This indicates that no new products of chain scission or polymer degradation are being generated.
Differential Scanning Calorimetry was used to determine crystallization temperatures and heat flow values on semi-crystalline polymers. Table 2 shows that there is no distinguishable effect of Vitrolite ® on polypropylene at loadings up to 2%.
Similar results are seen on linear low density polyethylene (LLDPE) at several loadings of Vitrolite ® (up to 20%). Figure 3 shows that the cooling curves are virtually identical other than the anticipated change in heat flow values with increasing Vitrolite ® content. These results show that Vitrolite ® does not affect crystallization kinetics or crystallite nucleation in polymers.
4. PHYSICAL TESTING
Physical testing of polymers processed with Vitrolite ® shows that polymer integrity has not been affected by the addition of Vitrolite ®. These tests have been done on a variety of polymers and the results are shown in Table 3 (for polypropylene and polyethylene) and Table 4 (for polycarbonate and polyamide).
From the testing, it is shown that Vitrolite ® does not cause any detectable changes to the chemical and crystallite structure or to the physical properties of the polymers. The rheological effects of Vitrolite ® on polymers are largely ascribed to a physical interaction of the polymer molecules with Vitrolite ® amorphous aluminosilicate particles prepared by a proprietary non-chemical process. Adding Vitrolite ® to plastics thus increases productivity and generates cost savings without alteration of the base polymer characteristics.
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