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Calcium carbonate (CaCO3) is one of the most popular mineral fillers used in the plastics industry. Its wide availability makes it an economical component in the production of polypropylene bags. CaCO3 helps as a whitener, lubricant, and finishing agent in the manufacturing of FIBCs. Used in the correct proportion, calcium carbonate also adds impact strength and flexural modulus giving bulk bags added performance and durability. Problem A chemical manufacturer, with a need to ship its product in bulk bags, found that its product created an adverse reaction with the calcium carbonate used in traditional FIBC production. This reaction significantly degraded the performance characteristics of the bulk bag. The manufacturer requested the technical assistance of Conitex Sonoco to develop a calcium-free polypropylene bulk bag container. Methodology 1. An Ash Content Analysis was performed on two re-engineered polypropylene sheets produced without calcium carbonate as a component. Testing was conducted on a Thermolyne Type 1400 muffle furnace per ASTM 5630 Standard Test Method for Ash Content in Thermoplastics, Procedure B-Rapid Ash Muffle Furnace Technique at 600ºC for 60 minutes. An Ohaus Analytical plus electronic balance was used for weight determination. Results of ASTM testing: In Sample A, the resultant average ash mass of calcium carbonate was a negligible .02%. For Sample B, the average ash mass was .06%. Both fabric sheets demonstrated extremely low remnant CaCO3 content. 2. A FTIR test, on similar re-engineered polypropylene sheets, was subsequently conducted with an infrared analysis using a Perkin Elmer Spectrum Two Model with a single bounce diamond ATR attachment.
Results of FTIR testing: Sample A and B results were nearly identical with the only difference being the oxidation due to the age of Sample A. The findings in the table above show that the re-engineered fabric samples contain only polypropylene functional groups with no trace of CaCO3. (see FTIR testing graph) Findings In the Ash Content Analysis, the re-engineered fabric passed as calcium free, reporting only a negligible trace amount of CaCO3. In the FTIR Perkin Elmer Spectrum test, only polypropylene functional groups were reported resulting in the fabric being determined as calcium free. Both tests, which tracked two sets of modified fabric, provided the same results. Conclusions Eliminating the calcium carbonate content in the production of the polypropylene bags resolved the degradation problem posed by the manufacturer’s chemical product. The manufacturer liked the visual fact that the bags were clear (demonstrating no use of CaCO3) and Conitex Sonoco substituted another low-cost lubricant in the manufacturing of the woven PP bags, thereby offsetting the two major contributing features of calcium carbonate. Conitex Sonoco also utilized a different UV inhibitor, which does not contain traces of CaCO3, to further meet the objectives of the manufacturer. Following a successful testing phase and approved bidding process, this manufacturer is now a BulkSak customer. For more information on Conitex Sonoco (Gastonia, NC), call 704-864-5406 or visit www.conitexbulksak.com.
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