Ideas
Exchange
Column
l&EC's features bring in lots of fan mail. Readers want information, and they pass along ideas. Ideas Exchange Column is a careful screening of this correspondence. This is not a place for praise or criticism; it is a source of technical questions and their factual answers.
Something Being Done DEAR SIR:
In the April issue of I&EC, H. F. Robertson of the Bakélite Co. stated the problem of nomenclature of the polyethylene resins. He said that identification of the resins by their properties could lead to such expressions as medium high tensile, moderately linear, or slightly branched. As one solution, Robertson called on the Society of the Plastics Industry or other suitable bodies to classify the polyethylene resins into a number of groups in much the same way that the spectrum is divided. Something is being done, and exactly along these same lines.
ASTM's Committee D-20 on Plastics (Subcommittee XV Thermoplastic Materials, Section J, ethylene plastics) has been looking into the problem of nomenclature of polyethylene resins, and has developed a system of classification based on dividing the resins into three main types, subdividing each type into four classes and then further subdividing each of the twelve classes into three grades. The system proposed by the ASTM committee has been balloted upon twice—that is, the original and the rewrite-^and rejected by a committee composed of both suppliers and users of the resins. Consequently, as yet, the
system has no status in ASTM or the industry. Below is a look at the proposed classification system which was voted upon and rejected in June 1957. The most prominent and repeated negative ballots were on the use of melt index in specified ranges as a classification criterion. The proposal is being rewritten to reconcile the negative ballots and will be voted upon at the next meeting of this subcommittee (XV, section J) of ASTM. Ε. Υ . WOLFORD
Koppers Co. Pittsburgh, Pa.
Requirements for Breakdown into Grades of Polyethylene Molding and Extrusion Materials Dielec Dielec Dielec tric tric tric Dissipa- ConDissipa Con Dissipa- Con tion stant", tion stant", tion stant", Factor", 1 K c Factor", 1 Kc. Factor·,, 1 K c Brittle 1 Kc. to to 1 Brittle 1 Kc. to to 1 Brittle 1 K c to to 1 Identifica Temp. 1 Mc. Mc. Absorp Temp. 1 Mc. Mc. Absorp- Temp. Mc. Absorp 1 Mc. S e c , tivity. tions S e c , S e c , tivity, Sec"C, Sec, S e c , tivity, ° C, °C, Max. Max. Min. Max. Max. Min. Max. Max. Min. Max. Max. Class Grade Max. Grade 1. Natural color only (general purpose and dielectric). Grade 2. Colors includ ing black (general pur pose and dielectric) con tain antioxidant unless otherwise agreed be tween vendor and pur chaser. Grade 3. Black only (weather resistant) con tains antioxidant unless otherwise agreed between vendor and purchaser, and not less than 2% car bon black no larger than 20-m/i average particle diameter.
Type I A
1 2 3
-60 -60 -60
0.0005 0.0005 0.005
2.30 2.35 2.75
1 2 3
-55 -55 -55
C
1 2 3
-45 -45 -45
D
1 2 3
-35 -35 -35
Β
Type II
24,000
-70 -70 -70
0.0005 0.0005 0.005
2.35 2.40 2.85
0.0005 0.0005 0.005
2.30 2.35 2.75 24,000
65 -65 -65
0.0005 0.0005 0.005
2.35 2.40 2.80
0.0005 0.0005
2.30 2.3S
0.0005 0.0005
2.35 2.40 2.80
Type III
24,000
-75 -75 -75
24,000
0.001 0.001 0.005
2.45 2.45 2.90
24,000
0.001 0.001 0.005
2.50 2.50 2.90
24,000
" Requirements apply only to materials to be used for electrical insulation.
Requirements for Breakdown into Types and Classes of Polyethylene Molding and Extrusion Materials Type I, Low Density Type II, Medium Density Type I I I , High Density Density Range", 0.910-0.925 Density Range" . 0.926-0.940 Density Range", 0.941-0.965 Class Class A Class Β Class C Class D Class A Class Β Class C Class D Class A Class Β Class C Class D Identification Melt index, g. per to 0.49 10 min.* 0.50-2.6 2.7-9.9 10-30 to 0.49 0 . 5 0 - 2 . 6 2.7-9.9 10-30 to 0.49 0.50-2.6 2.7-9.9 10-30 Tensile strength, min. lb./sq. in. 1600 1000 800 2200 2000 1400 1800 1600 1200 1000 400 200 20 Ultimate elonga 400 400 400 50 5 20 5 tion, min. % Environmental crack resist., max. 20% at 48 hr. « At 23° C , of uncolored, unfilled specimen. * An indication of uniformity of flow rate of the polymer of a single manufacturer, made by an individual process, and may indicate uniformity of other properties. However, flow-rate uniformity of various polymers from various manufacturers, made by various processes, does not, in the absence of other tests, indicate uniformity of other properties.
VOL. 49, NO. 8
·
AUGUST 1957
83 A
