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COMPARISON AND MATCHING OF LOW DENSITY POLYETHYLENE PLASTIC BAGS BY INFRARED SPECTROSCOPY

NCJ Number
57023
Journal
Journal of Forensic Sciences Volume: 24 Issue: 2 Dated: (APRIL 1979) Pages: 339-345
Author(s)
B CLEVERLEY
Date Published
1979
Length
7 pages
Annotation
COMMON LOW-DENSITY POLYETHYLENE (LDPE) BAGS ARE USED TO PACKAGE ILLEGAL DRUGS AND ARE OFTEN FOUND ASSOCIATED WITH OTHER CRIMES. A METHOD OF AMPLIFYING WEAK INFRARED ABSORPTION BANDS TO MATCH LDPE FILMS IS DESCRIBED.
Abstract
WEAK TO MEDIUM BANDS IN THE INFRARED SPECTRA OF COMPARATIVELY THICK FILMS ARE COMMONLY USED TO DISTINGUISH HIGH- AND LOW-DENSITY POLYETHYLENES, BUT THE SPECTRAL DIFFERENCES GENERALLY ARE NOT SUFFICIENT TO ENABLE DIFFERENT LDPE RESINS TO BE DIFFERENTIATED. CONSEQUENTLY, A TECHNIQUE FOR INTENSIFYING THESE WEAK BANDS WAS DEVELOPED. WADS OF LDPE FILM WERE COMPRESSED INTO THICK TRANSPARENT FILMS AT A TEMPERATURE BELOW THEIR MELTING POINT. THESE PELLETS WERE THEN ANALYZED ON A PERKIN-ELMER MODEL 580 SPECTROPHOTOMETER WITH THE INTEGRATED SCAN MODE SET AT 2. ADDITIONAL NOISE FILTERING WAS USED TO OBTAIN CLEAR READINGS. ANALYSIS OF FILM SPECTRA FROM ELEVEN COMMERCIAL RESINS SUPPLIED BY POLYMER MANUFACTURERS IN CANADA, GREAT BRITAIN, JAPAN, AND THE U.S. REVEALED THAT ALL BUT TWO WERE DIFFERENT. FOR THESE TWO, THE ADDITION OF SLIP AND ANTIBLOCKING AGENTS PROVIDED A MEANS OF DIFFERENTIATION. TWENTY-NINE PACKS OF BAGS, PRODUCED IN 16 DIFFERENT SHAPES AND SIZES BY 7 DIFFERENT BAG MAKERS, WERE NEXT EXAMINED, AND 19 DIFFERING POLYMER SPECTRA WERE OBTAINED. (BAG MANUFACTURERS OFTEN USE THE SAME FILM FOR DIFFERENT SIZES AND DIFFERENT MANUFACTURERS MAY USE SIMILAR POLYMERS.) THESE SPECTRA ARE ILLUSTRATED AND ANALYZED. THE MOST USEFUL FINDING WAS THAT DIFFERENT RESINS MAY BE USED AT DIFFERENT TIMES FOR THE SAME KIND OF BAG. SEVEN PACKS PURCHASED IN DIFFERENT PLACES AROUND THE CITY HAD THREE TYPES OF POLYMERS, WHILE OTHER PRODUCTS VARIED OVER TIME IN THE POLYMERS USED. THIS HAS FORENSIC APPLICATIONS. (GLR)

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