Additional steps in mechanical recyling of PET

This study presents the laboratory scale results of an extra step in Poly (ethylene terephthalate) - PET mechanical recycling (grinding, washing, drying and reprocessing): a chemical washing after the conventional one. Cooking oil PET bottle flakes were washed in water and then subjected to a reaction with an aqueous solution of sodium hydroxide 5 M at 90 degrees C for 10 min (chemical washing). After rinsing and drying, the flakes were characterized by thermogravimetry, gas chromatography and elemental analysis tests. The results indicated that the chemically washed material had higher purity than PET washed only with water: 99.3% and 96.7%, respectively, which undoubtedly implies properties, applications and prices closer to those of virgin resin. The production of purified terephthalic acid (TPA) from the chemical washing residue was optimized and reached a purity of 99.6%. Despite the results, the use of chemically washed PET and of TPA obtained is not recommended for direct contact with food, since they still contain some impurities. (C) 2009 Elsevier Ltd. All rights reserved.

Construction and demolition waste as a source of PVC for recycling

Construction and demolition waste can contain considerable amounts of polyvinyl chloride (PVC). This paper describes a study of the recycling of PVC pipes collected from such waste materials. In a sorting facility for the specific disposal of construction and demolition waste, PVC was found to represent one-third of the plastics separated by workers. Pipes were sorted carefully to preclude any possible contamination by poly(ethylene terephthalate) (PET) found in the waste. The material was ground into two distinct particle sizes (final mesh of 12.7 and 8 mm), washed, dried and recycled. The average formulation of the pipes was determined based on ash content tests and used in the fabrication of a similar compound made mainly of virgin PVC. Samples of recycled pipes and of compound based on virgin material were subjected to tensile and impact tests and provided very similar results. These results are a good indication of the application potential of the recycled material and of the fact that longer grinding to obtain finer particles is not necessarily beneficial.

Population structure of pond-raised Macrobrachium amazonicum with different stocking and harvesting strategies

The effect of size-grading of juveniles prior to stocking, as well as selective harvesting, on the population structure of pond-raised Macrobrachium amazonicum was studied. A randomized-complete-blocks design with 4 treatments and 3 replicates was used. The treatments were: upper size-graded juveniles, lower size-graded juveniles, ungraded juveniles (traditional), and ungraded juveniles with selective harvesting. Twelve 0.01 ha earthen ponds were stocked at 40 juveniles m(-2), according to the relevant treatment. Every three weeks, random samples from each pond were obtained for biometry, and after 3.5 months, the ponds were drained and completely harvested. Animals were then counted, weighed, and sexed; males were sorted as Translucent Claw (TC), Cinnamon Claw (CC), Green Claw 1 (GC1), and Green Claw 2 (GC2), and females as Virgin (VF), Berried (BE), and Open (OF). The prawns developed rapidly in the ponds. attaining maturity and differentiating into male morphotypes after about 2 months in all treatments. The fast-growing juveniles (upper grading fraction) mostly did not constitute the dominant males (CC] and GC2) in the adult population. Population development was slower in ponds stocked with Lower prawns, whereas selective harvesting increased the frequency of GC1 and reduced the final mean weight of GC2 males. The proportion of males increased throughout the culture period, but was generally not affected by the stocking or harvesting strategies. Grading juveniles and selective harvesting slightly altered the population dynamics and structure, although the general population development showed similar patterns in ponds stocked with upper, lower, and ungraded juveniles, or selectively harvested. (C) 2010 Elsevier B.V. All rights reserved.