PHYSICOCHEMICAL TESTS—PLASTICS
The following tests,designed to determine physical and chemical properties of plastics and their extracts,are based on the extraction of the plastic material,and it is essential that the designated amount of the plastic be used.Also,the specified surface area must be available for extraction at the designated temperature.
Extracting Medium— Unless otherwise directed in a specific test below,use Purified Water(see monograph)as the extracting medium,maintained at a temperature of 70during the extraction of the prepared Sample.
Apparatus— Use a water bath and the Extraction Containersas described under Biological Reactivity Tests,In Vivo á88ñ.
Preparation of Apparatus— Proceed as directed in the first paragraph of Preparation of Apparatusunder Biological Reactivity Tests,In Vivo á88ñ.[NOTE—The containers and equipment need not be sterile.]
Procedure—
Preparation of Sample— From a homogeneous plastic specimen,use a portion,for each 20.0mLof extracting medium,equivalent to 120cm2total surface area (both sides combined),and subdivide into strips approximately 3mm in width and as near to 5cm in length as is practical.Transfer the subdivided Sampleto a glass-stoppered,250-mLgraduated cylinder of Type Iglass,and add about 150mLof Purified Water.Agitate for about 30seconds,drain off and discard the liquid,and repeat with a second washing.
Transfer the prepared Sampleto a suitable extraction flask,and add the required amount of Extracting Medium.Extract by heating in a water bath at the temperature specified for the Extracting Mediumfor 24hours.Cool,but not below 20.Pipet 20mLof the extract of the prepared Sampleinto a suitable container.Use this portion in the test for Buffering Capacity.Immediately decant the remaining extract into a suitably cleansed container,and seal.
Blank— Use Purified Waterwhere a blank is specified in the following tests.
NONVOLATILERESIDUE— Transfer,in suitable portions,50.0mLof the extract of the prepared Sampleto a suitable,tared crucible (preferably a fused-silica crucible that has been acid-cleaned),and evaporate the volatile matter on a steam bath.Similarly evaporate 50.0mLof the Blankin a second crucible.[NOTE—If an oily residue is expected,inspect the crucible repeatedly during the evaporation and drying period,and reduce the amount of heat if the oil tends to creep along the walls of the crucible.]Dry at 105for 1hour:the difference between the amounts obtained from the Sampleand the Blankdoes not exceed 15mg.
RESIDUEONIGNITIONá281ñ— [NOTE—It is not necessary to perform this test when the Nonvolatile Residuetest result does not exceed 5mg.]Proceed with the Nonvolatile Residueobtained from the Sampleand from the Blank,using,if necessary,additional sulfuric acid but adding the same amount of sulfuric acid to each crucible:the difference between the amounts of residue on ignition obtained from the Sampleand the Blankdoes not exceed 5mg.
HEAVYMETALS— Pipet 20mLof the extract of the prepared Sample,filtered if necessary,into one of two matched 50-mLcolor-comparison tubes.Adjust with 1Nacetic acid or 6Nammonium hydroxide to a pHbetween 3.0and 4.0,using short-range pHpaper as external indicator,dilute with water to about 35mL,and mix.
Into the second color-comparison tube pipet 2mLof Standard Lead Solution(see Heavy Metals á231ñ),and add 20mLof the Blank.Adjust with 1Nacetic acid or 6Nammonium hydroxide to a pHbetween 3.0and 4.0,using short-range pHpaper as external indicator,dilute with water to about 35mL,and mix.To each tube add 1.2mLof thioacetamide-glycerin base TSand 2mLof pH3.5Acetate Buffer(see Heavy Metals á231ñ),dilute with water to 50mL,and mix:any brown color produced within 10minutes in the tube containing the extract of the prepared Sampledoes not exceed that in the tube containing the Standard Lead Solution,both tubes being viewed downward over a white surface (1ppm in extract).
BUFFERINGCAPACITY— Titrate the previously collected 20-mLportion of the extract of the prepared Samplepotentiometrically to a pHof 7.0,using either 0.010Nhydrochloric acid or 0.010Nsodium hydroxide,as required.Treat a 20.0-mLportion of the Blanksimilarly:if the same titrant was required for both Sampleand Blank,the difference between the two volumes is not greater than 10.0mL;and if acid was required for either the Sampleor the Blankand alkali for the other,the total of the two volumes required is not greater than 10.0mL.