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Anal. Chem. 1980, 52. 2225-2226
volume collected (9). An obvious disadvantage of the system reported is that no repetitive determinations are possible for each sample. However, the most important advancements that this system offers are minimum sampling time with accurate sample volume determination.
LITERATURE CITED (1) Middleton, J. T. "Research in Pesticides"; Chichester, C. O., Ed.; Academic Press: New York. 1965; p 191. (2) Wheatley, G. A. "Environmental Pollution by Pesticides"; Edwards, C.A.. Ed.; Plenum Press: London, 1973; p 365. (3) Gerakis, P. A.; Sticas, A. G. Residue Rev. 1974, 52, 69. (4) Seiber, J. N.; Woodrow, J. E.; Safik, T. M.; Enos, H. F. "Environmental Dynamics of Pesticides": Hoaue, R. Freed, V. H., Eds.; Plenum Press: New York, 1975; p 17. (5) Miles, J. W.; Fetzer, L. E.; Pearce, G. W. Environ. Sci. Tech. 1970, 4 , 420 (6) Van Dyk, L. P.; Visweswariah, K. ResMue Rev. 1975, 55, 91. (7) Lee, R. E., Jr. "Air Pollution from Pesticaes and Agricukural Processes"; Chemical Rubber Co. Press: Cleveland, 1976. (8) Linch, A. L. "Evaluation of Ambient Air Quality by Personnel Monitoring"; Chemical Rubber Co. Press: Cleveland, 1976. (9) Melcher, R. G.; Langner, R. R.; Kagel, R. 0. Am. Ind. Hyg. Assoc. J . 1970, 39,349.
-
Figure 3. Gas flow diagram for sample desorber apparatus. Position 1 indicates flow pattern for purge functional mode, and position 2 indicates flow pattern for injection mode.
utilizing liquid concentration media) and rely on precalibration of pumping speeds. Many factors can change pressure drops across the trapping medium during sampling, including: humidity, viscosity, sample loading, friction, supply voltage changes, etc., which may significantly alter estimates of total
RECEIVED for review February 1, 1980. Resubmitted May 21, 1980. Accepted August 7, 1980.
Separation of Composite Polymer Film Layers Barry Cleverley Chemistry Division, Department of Scientific & Industrial Research, Private Bag, Petone, New Zealand
It is usually necessary t o separate some of t h e layers t h a t make up a composite polymer film before the composition of t h e film or the order of t h e layers can be determined. T h e separated layers can be identified in various ways. infrared spectroscopy being t h e best single method since samples are easily prepared from films and every polymer has a characteristic infrared spectrum. EXPERIMENTAL SECTION Some film layers were separated intact, but thin outer coatings were usually separated by abrasion or dissolution, and some soluble layers were best isolated with solvents. Removal of Thin S u r f a c e Coatings. Thin coatings on the surfaces of film layers are usually nitrocellulose coatings on cellulose-based films or poly(viny1idene chloride) copolymers coated on almost any kind of polymer substrate. Abrasive Paper. The coatings may be removed with dry abrasive paper from hard substrate f i i such as cellulose, polyamide, and polyester. Cut a strip of film about 3 cm wide, along the machine direction for strength. Lay it on a clean glass plate and rub, one way only, with a 3-cm strip of 180 or 240 grit abrasive paper which has been folded double to provide a grip. Collect the powdered coating from the paper and the glass plate with a single-edge blade, and incorporate in a potassium bromide pellet for identification by infrared spectroscopy. Soluents. Soluble coatings can be removed with solvents. Cut the fiim into pieces that can lie on the bottom of a 150-mL conical flask. To provide free access for the solvent to both surfaces of the film,crinkle the pieces so they will not cling together or stick to the glass. Pour a small amount of solvent into the flask, shake very briefly, and then pour out. Repeat the procedure until the coating has all been removed. By minimum contact with the solvent in this way, soluble materials within the composite structure will not be dissolved. 0003-2700/80/0352-2225$01 .OO/O
Spread the solution on a clean glass plate or the bottom of a Petri dish and allow the solvent to evaporate slowly. Remove the dry polymer f h under water, with the aid of a thin blade. Fragile films that are difficult to handle can be manipulated successfully under water. Nitrocellulose coatings are soluble in cold methanol. Plasticizers in the coating which interfere with identification should be removed by first rinsing quickly four times with cold dichloromethane. Once the film is dry again, two quick rinses with cold methanol should be all that is needed to remove the coating. Longer contact with methanol may remove some of the softener from the cellulose base film. Coatings of poly(viny1idene chloride) copolymers are removed from films by rinsing quickly a few times with cold tetrahydrofuran. Tetrahydrofuran generally contains hydroquinone which can be removed from films that have been cast from solutions of tetrahydrofuran by soaking in hot water. Removal o f t h e Coating f r o m O n e Side of a Composite Film. The coating can be removed from only one side of a composite film either by abrasion or by pouring solvent into a container made by stretching the film across one end of an open tube. An ideal vessel can be made from an 8 cm diameter preserving jar with the bottom removed. Seal off the other end by squeezing the f i i between the rim of the jar and the rubber-lined sealing dome. Secure the dome in place with adhesive tape. The film must be dried quickly once the coating has been removed or the solvent may penetrate the composite structure, dissolving additives and other polymer layers, including any coating there may be on the other surface of the film. Separation of Film L a y e r s by Soaking. Some composite films delaminate when they are wet and although this may be a short-coming during use, it can be turned to advantage by the analyst. Cut the film into 3-cm squares and soak in the appropriate liquid (Table I). After a time the layers will separate when one corner of each square has been stretched and scraped. The 0 1980 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980
Table I. Examples of the Separation of Composite Film Layers by Soaking in Wetting Liquids soaking time for 3-ern squares, min
structure of composite filma
separation achieved
Separation in Boiling Water cellulose - based film PVDC coating/cellulose/PU adhesive/PE/ PV DC/coating PE/PET films PE/PET PVDC coating/PE/PU adhesive/PET poly (olefin )/PVDC films PP/PVDC layer/EVA EVAIPVDC layer/EVA PE/PU adhesive/PVDC coating/PA
15
PVDC coating/cellulose ;PU/PE/ PVDC coating
15
PEPET PVDC coating/PE/PU P E T
30
PP PVDC ;EVA EVA;PVDC;EVA PE;PU/PVDC coating/PA
60 60
120
Separation in Cold Tetrahydrofuran PE/PA films with adhesive EVAfionomer/PA PE/PU adhesive/PA
2
EVA/ionomer;PA PE;PU/PA
10
a Key to abbreviations: PVDC, poly(viny1idene chloride); PU, polyurethane; PE, poly(ethy1ene); PET, polyester; PP, poly(propy1ene ); EVA, ethylene vinylacetate; PA, polyamide.
Table 11. Separation of Composite Polymer Film Layers by Selective Solubility soaking time for 3-em squares, min
structure of composite film
separation achieved
PA in Cold 90% Formic Acid PA/PU adhesive/PE PA/ionomer/PE
PA (soltn);PU/PE PA (soltn)jonomer/PE
a a
PE in Hot Toluene PE/PU
PE (so1tn);PU
1
PVDC in Cold Tetrahydrofuran PA/PU adhesive/PVDC coating/PE PP/PVDC layer/EVA EVA/PVDC layer/EVA PET/PU adhesive/PE/PVDC coating
PA;PVDC (soltn)PU/PE PP;PVDC (so1tn);EVA EVA;PVDC (so1tn);EVA PET ;PU/PE ;PVDC (soltn )
5 5 10 5
PVDC in Cold Dioxane PVDC layer/PVDC coating/PVDC layer a
2
PVDC (so1tn);PVDC fi1m;PVDC (soltn)
Overnight.
films can then be pulled apart from the corners. Films should be soaked for as short a time as possible so that there is no unnecessary loss of soluble materials into the wetting liquid. Separation w i t h Solvents. Many solvents tend to dissolve a number of polymers and the separation of film layers using solvents has limited application. Cut film into 3-em squares and soak in solvent (Table 11).
RESULTS AND DISCUSSION Examination of a number of commercial composite films of known structure has shown which separation procedures are the most effective with certain polymer film combinations. Soaking. T h e conditions for separating some commercial cellulose-, polyester-, and polyamide-based films and some poly(viny1idene chloride)/polyolefin combinations have been found, Table I. Cellulose-based films tended to delaminate in hot water. Polyolefin layers usually separated from polyester and poly(viny1idene chloride) layers quite readily in hot water, but polyethylene/polyamide composite films in which the layers had been joined with a polyurethane adhesive or a n ionomer layer separated only after soaking in cold tetrahydrofuran long enough to just soften the adhesive layers.
Poly(viny1idene chloride) coatings remained attached to their supporting layers after soaking in boiling water under the conditions in Table I, but they could be rubbed off cellulose layers that had been in boiling water longer than 30 min. Coatings which had been deposited on the supporting film from an aqueous suspension were removed more readily than those that had been applied as solutions. Solvents. Polyamide layers were dissolved by overnight soaking in cold 90% formic acid. Low-density polyethylene and ethylenevinyl acetate copolymers dissolved in hot toluene but the ionomers studied melted without dissolving. Although all the poly(viny1idene chloride) coatings and layers examined were soluble in cold tetrahydrofuran, it was possible t o distinguish between the components of a composite film made from two different poly(vinylidene chloride) copolymers since one copolymer was soluble in cold dioxane and the other was not. Examples of the separation of some composite polymer film layers by selective solubility are presented in Table 11.
RECEIWD for review March 18,1980. Accepted July 21,1980.
