Abstract
An estimation procedure for biobased carbon content of polyethylene composite was studied using carbon-14 (14C) concentration ratios as measured by accelerated mass spectrometry (AMS). Prior to the measurement, additives and fillers in composites should be removed because they often contain a large amount of biobased carbon and may shift the estimation. Samples of resin with purity suitable for measurement were isolated from composites with a Soxhlet extractor using heated cyclohexanone. After cooling of extraction solutions, the resin was recovered as a fine semi-crystalline precipitate, which was easily filtered. Recovery rates were almost identical (99%), even for low-density polyethylene and linear low-density polyethylene, which may have lower crystallinity. This procedure could provide a suitable approach for estimation of biobased carbon content by AMS on the basis of the standard ASTM D 6866. The biobased carbon content for resin extracted from polyethylene composites allow for the calculation of biosynthetic polymer content, which is an indicator of mass percentage of the biobased plastic resin in the composite.
Highlights
Biobased plastics such as poly(lactic acid) and poly(hydroxyl alkanoic acid) are already produced commercially and are steadily gaining in popularity with public awareness of the environment
The Soxhlet extractor is a sophisticated instrument for lab work, and the extraction of resin proceeded smoothly once a heating program was properly set with reference to an instruction provided by Büchi Co
In a preliminary experiment using resin pellets, completion of resin extraction could be confirmed via weight change of the extraction thimble before and after the operation. This was due to the low hygroscopicity of the extraction thimble; a small amount of remaining resin in the extraction thimble could be confidently detected
Summary
Biobased plastics such as poly(lactic acid) and poly(hydroxyl alkanoic acid) are already produced commercially and are steadily gaining in popularity with public awareness of the environment. The biobased carbon ratios of plastics can be estimated by the ratio of 14C to 12C measured by accelerator mass spectrometry (AMS) conforming to the standard ASTM D 6866 “Standard Test Methods for Determining the Biobased Content of Natural Range Materials Using Radiocarbon and Isotope Ratio Mass Spectrometry Analysis.”. After cooling the extraction solution, resin components should form a dense precipitate and be successfully recovered by filtration of the entire extraction solution Fillers such as graphite, calcium carbonate, starch, and cellulose are insoluble in hydrophobic solvents and remain in an extraction thimble throughout the operation. Filtering the floating polyethylene precipitate and rinsing with a volatile solvent can yield a good sample with purity suitable for AMS measurement, and at the same time, can provide an estimate of the amount of resin content of composites. Physical properties of the precipitates were studied by scanning-electron microscope observation, differential scanning calorimetry (DSC), X-ray diffraction, and UV-visible measurements to confirm crystallinity of the precipitates and adequate removal of the additive from the composites
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