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Reprinted (romReçu le '- 8 DEC.1969

PERGAMON PRESSOXFORD'NEW YORK LONDON PARIS

Ta1anta. 1967. Vol. 14. pp. 421 to 424. Pergamon Press Lld. Printed in Northern lreland

CHARACTERIZATION AND ANALYSIS OF WAXESBY DIFFERENTIAL THERMAL ANALYSIS

B. R. CURRELL

Department of Chemistry, Northern Polytechnic, Holloway Road, London, N.7, U.K.and

B. ROBINSONChiswick Products Ltd., P.O. Box 26, Burlington Lane,

Chiswick, London, W.4, U.K.

(Received 15 September 1966)

Summary- The characterization of waxes by differential thermalanalysis is described. An endothermic peak at 475-480° is character­istic of microcrystalline and polyethylene waxes, and measurementof its area provides a method for the estimation of these waxes inmixtures.

RECENT interest in the characterization of paraffin and microcrystalline waxes andin the analysis of mixtures of these waxes is typified by the papers by Ferris,l FOX,2Templin3 and Ludwig.4 Lange and Jochinke5 have applied differential thermalanalysis (DTA) to a study of the melting and solidification of waxes (temperaturerange 20-140°) and suggest that these curves may be used to characterize a wax andin many cases to determine the components of a mixture. We have similarly appliedDTA but, in our case, in the range 20-600°.

From our studies of the melting curves we draw the same general conclusions asLange and Jochinke and suggest that, to a possibly limited extent, these curves maybe used to characterize a wax. The melting curves do not give unequivocal criteriafor distinguishing between microcrystalline and polyethylene waxes and paraffinwaxes, but there is a tendency for most microcrystalline and polyethylene waxes tobe characterized by a single melting endotherm (Fig. 2), whereas the paraffin waxesshow at least two endotherms CFig. 1). Exceptions to this tendency are the Superla165/170° and Jasber 180/185° waxes (e and h, Fig. 2) and the 140/145° ex Assam andthe 56/58° German Zeitz waxes (jandj, Fig. 1). The additional peaks in the paraffinwax traces may be due to the crystalline transition orthorhombic -+ hexagonal whichLudwig detected by infrared spectra.

DTA in the extended temperature range up to 600° does, however, provide a

ready means of distinguishing between microcrystalline and polyethylene waxes andparaffin waxes. At the higher temperatures aIl the paraffin waxes showed broaddiffuse peaks which returned to baseline before 460°. ln contrast, a sharp peak at475-480° is characteristic of all the microcrystalline and polyethylene waxes which wehave examined. This peak may be used to identify the presence of a microcrystallineor polyethylene wax in a mixture and also to give a quantitative estimation of theamount present; thus Table l shows the results obtained by measuring the area ofthis peak and relating it to the amount of microwax C700 in an artificial mixture ofthis microwax and the paraffin wax 135/140° exStanlow Refinery. The DTA traceof the mixture containing 50,0 % of microwax is reproduced in Fig. 3.

421

a v---Y .j:>.NN

!:Ai

(d

()

1!»::s0-

~~otlj

~~

~

)0 SoCh

oxW

1 1 1 1 1 1 1 1 1 1 1 1 1

o 100 200 300 400 SOO 0 100 200 300 400 SOO

Temperature, ·C

Fm. l.-DTA curves of paraffin waxes.a, 135/140 ex Stanlow Refinery, sample 1; b, 135{140 ex Stanlow Refinery,Sample 2; c, 140{145 ex Stanlow Refinery, sample 1; d, 140{145ex StanlowRefinery, sample 2; e, 120{125 ex B.P. Trading Co; f, 140/145 ex Assam;g, 135{140 ex Assam; h, 52{54 Russian; i, 52/54, German, Kopsen Webau;

j, 56/58 German, Zeitz.

k

1 1 1 1 1 1 1 1 1 1 1 1 1

o œ = ~ ~ = 0 œ = ~ ~ =Temperature, ·C

Fm. 2.-DTA curves of micro and polyethylene waxes.a, Microwax C23; b, Microwax C700; c, Superwax Amber 1800; d, StarwaxAmber 180°; e, Superla 165{170; f, Superla 165{170; g, Bareco Amber;h, Jasber 180{185°; i, Polyethylene PA130; j, Polyethylene AC 629; k, Poly-

ethylene AC6.

e

Characterization and analysis of waxes by differential thermal analysis 423

Exo

En'do

lo

J

100L--J

200 300Temperoture,

J

400

·C

J

500

Fm. 3.-DTA curve of 1: 1 mixture of microwax C23 and paraffin wax 135{140 exStanlow Refinery.

The shaded area gives a measure of the amount of microwax present (see Table 1).

TABLEL-TypICAL RESULTSOBTAINEDlN THEANALYSISOF MIXTURESOF MICROWAXC700AND PARAFFINWAX 135{40 ex STANLOW

REFlNERY

Microwax

present, %

Microwax found bymeasuring the area of the,

peak at 475°, %

71·950,047·219·2

67-353'951-615·6

o"w

L-J100 200

1

o 1 1 1 1 1 1 1 1 1

300 400 500 0 100 200 300 400 500Temperature, ·C

FIG. 4.-DT A curves of waxes.a Hoechst Wax L; b, Hoechst Wax OM; c, Candelilla Wax; d, Beeswax; e, Carnauba

Flake.

424 B. R. CURRELLand B. ROBINSON

To provide a comparison the DTA traces of sorne other waxes are included (Fig.4). These include the natural waxes Beeswax, Candelilla and Carnauba Plake and thesynthetic Hoechst waxes Land OMo

These resuIts are preliminary; a full evaluation of the limitations of this methodof analysing wax mixtures will be carried out when we have finished a programme ofwork designed to define the limitations of DTA as a quantitative method; factors tobe taken into account will include variations in the size and thermal conductivity ofthe samples, heating rate, crucible design and methods of packing.

EXPERIMENT AL

The apparatus used was the American Instrument Co. DTA instrument. The sample (~100 mg)and reference material (calcined alumina) were contained in inconel cups, the bases ofwhich rested onchromel-alumel thermocouples; the cups were supported in an inconel block. Differentiai temperaturewas plotted against block temperature on an Aminco X-Y recorder. Ail runs were carried out at aheating rate of 8°/min.

To obtain maximum reproducibility in the quantitative experiments the same components, i.e.,cups, block and furnace, were used throughout. The pair of cups used were chosen to be as nearly aspossible of the same weight.

Acknawledgements-We wish to acknowledge the generosity of the American Instrument Co. inproviding the DT A equipment on loan, and also the experimental assistance given by Mr. P. Stevenson,who carried out many of the runs.

Zusammenfassung-Die Charakterisierung von Wachsen durchDifferentialthermoanalyse wird beschrieben. Ein endothermer Peakbei 475-480° ist charakteristisch für mikrokristalline und Polyathylen­wachse; Messung seiner Flache bietet eine Methode zur Bestimmungdieser Wachse in Gemischen.

Résumé-On décrit la caractérisation de cires par analyse thermiquedifférentielle. Un pic endothermique à 475-480° est caractéristique decires microcristallines et polyéthyléniques et la mesure de son airefournit une méthode d'estimation de ces cires dans des mélanges.

REFERENCES

1. S. W. Ferris, Tech. Assac., Paper Pulp lnd., Spec. Tech. Assac. Publ., 1963, 2, 1.2. R. C. Fox, ibid. 1963,2,160.3. P. R. Templin, ibid. 1963, 2, 51.4. F. J. Ludwig, Anal. Chem., 1965, 37, 1737.5. J. Lange and H. Jochinke, Fette Seifen Anstrichmittel, 1965, 67, 89.