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Characterization and analysis of waxes by differential thermal analysis
Tabma. 1967.Vol. 14.pp. 421to 424. PcrgamonPces.s Ltd. Printedin Northem Ireland
CHARACTERIZATION AND ANALYSIS OF WAXES BY DIFFERENTIAL THERMAL ANALYSIS B. R. Department
of Chemistry, Northern
CURRELL
Polytechnic,
Holloway Road, London, N.7, U.K.
and
B. ROBINSON Chiswick 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 thermal analysis is described. An endothermic peak at 475480” is characteristic of microcrystalline and polyethylene waxes, and measurement of its area provides a method for the estimation of these waxes in mixtures. RECENT interest in the characterization of paraffin and microcrystalline waxes and in the analysis of mixtures of these waxes is typified by the papers by Ferris,l Fox,~ Templin3 and Ludwig.” Lange and Jochinke 5 have applied differential thermal analysis (DTA) to a study of the melting and solidification of waxes (temperature range 20-140’) and suggest that these curves may be used to characterize a wax and in many cases to determine the components of a mixture. We have similarly applied DTA but, in our case, in the range 20-600”. From our studies of the melting curves we draw the same general conclusions as Lange and Jochinke and suggest that, to a possibly limited extent, these curves may be used to characterize a wax. The melting curves do not give unequivocal criteria for distinguishing between microcrystalline and polyethylene waxes and paraffin waxes, but there is a tendency for most microcrystalline and polyethylene waxes to be characterized by a single melting endotherm (Fig. 2), whereas the paraffin waxes show at least two endotherms (Fig. 1). Exceptions to this tendency are the Superla 165/170” and Jasber 180/185” waxes (e and h, Fig. 2) and the 140/145” ex Assam and the 56/58O German Zeitz waxes (fand j, Fig. 1). The additional peaks in the paraffin wax traces may be due to the crystalline transition orthorhombic + hexagonal which Ludwig 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 and paraffin waxes. At the higher temperatures all the paraffin waxes showed broad diffuse peaks which returned to baseline before 460”. In contrast, a sharp peak at 475-480” is characteristic of all the microcrystalline and polyethylene waxes which we have examined. This peak may be used to identify the presence of a microcrystalline or polyethylene wax in a mixture and also to give a quantitative estimation of the amount present; thus Table I shows the results obtained by measuring the area of this peak and relating it to the amount of microwax C700 in an artificial mixture of this microwax and the paraffin wax 135/140” ex Stanlow Refinery. The DTA trace of the mixture containing 50.0 % of microwax is reproduced in Fig. 3.
421
Characterization
and analysis of waxes by differential thermal analysis
I
0
I
I
loo
200
I 400
I 300
T-UN.
I so0
1
.C
curve of 1: 1 mixture of microwax C23 and par& wax 135/140 ex Stanlow Refinery. The shaded area gives a measure of the amount of microwax present (see Table 1). FIG.
3.-DTA
TABLEI.-TYPICAL RESULTSOBTAINED ANALYSIS AND
OF
MIXTURJZS
PARAFFIN
WAX
OF
MICROWAX
135140 ex
IN
THE
000
STBUW
REFINERY
Microwax present, %
Microwax found by measuring the area of the peak at 475”. %
71.9 50.0 47.2 19.2
67.3 53.9 51.6 15.6
Tamw~roture,
=C
4.-DTA curves of waxes. a Hoechst Wax L; b, Hoechst Wax OM ; c. Candelilla Wax; d, Beeswax; e, Carnauba Flake. FIG.
423
424
B. R. C-L
and B. ROBINSON
To provide a comparison the DTA traces of some other waxes are included (Fig. 4). These include the natural waxes Beeswax, Candelilla and Carnauba Flake and the synthetic Hoechst waxes L and OM. These results are preliminary; a full evaluation of the limitations of this method of analysing wax mixtures will be carried out when we have finished a programme of work designed to define the limitations of DTA as a quantitative method; factors to be taken into account will include variations in the size and thermal conductivity of the samples, heating rate, crucible design and methods of packing. EXPERIMENTAL 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 of which rested OD chromel-ahnnel thermocouples; the cups were supported in an inconel block. Differentialtemperature was plotted against block temperature on an Aminco X-Y recorder. All runs were carried out at a heating rate of 8O/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 as possible of the same weight. Acknowle&ements-We wish to acknowledge the generosity of the American Instrument Co. in providing the DTA equipment on loan, andalso theexperimentalassistancegiven by Mr. P. Stevenson, who carried out many of the runs. Zusammenfassung-Die Charakterisierung von Wachsen durch Differentialthermoanalyse wird beschrieben. Ein endothermer Peak bei 475-480” ist charakteristisch fiir mikrokristalline und Polyiithylenwachse; Messung seiner Fliiche bietet eine Methode zur Bestimmung dieser Wachse in Gemischen. R&&---On d&it la caracterisation de tires par analyse thermique differentielle. Un pit endothermique a 475-480” est caract6ristique de tires microcristallines et poly&hyl&iques et la mesure de son aire foumit une mtthode d’estimation de ces tires dam des melanges. REFERENCES 1. 2. 3. 4. 5.
S. W. Ferris, Tech. Assoc., Paper Pu& Ind., Spec. Tech. Assoc. Publ., 1963, 2, 1. R. C. Fox, ibid. 1963, 2, 160. P. R. Templin, ibid. 1963, 2, 51. F. J. Ludwig, Anal. Chem., 1965,37, 1737. J. Lange and H. Jochinke, Fette Seifen Anstrichmittel, 1965, 67, 89.
CHARACTERIZATION AND ANALYSIS OF WAXES BY DIFFERENTIAL THERMAL ANALYSIS B. R. Department
of Chemistry, Northern
CURRELL
Polytechnic,
Holloway Road, London, N.7, U.K.
and
B. ROBINSON Chiswick 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 thermal analysis is described. An endothermic peak at 475480” is characteristic of microcrystalline and polyethylene waxes, and measurement of its area provides a method for the estimation of these waxes in mixtures. RECENT interest in the characterization of paraffin and microcrystalline waxes and in the analysis of mixtures of these waxes is typified by the papers by Ferris,l Fox,~ Templin3 and Ludwig.” Lange and Jochinke 5 have applied differential thermal analysis (DTA) to a study of the melting and solidification of waxes (temperature range 20-140’) and suggest that these curves may be used to characterize a wax and in many cases to determine the components of a mixture. We have similarly applied DTA but, in our case, in the range 20-600”. From our studies of the melting curves we draw the same general conclusions as Lange and Jochinke and suggest that, to a possibly limited extent, these curves may be used to characterize a wax. The melting curves do not give unequivocal criteria for distinguishing between microcrystalline and polyethylene waxes and paraffin waxes, but there is a tendency for most microcrystalline and polyethylene waxes to be characterized by a single melting endotherm (Fig. 2), whereas the paraffin waxes show at least two endotherms (Fig. 1). Exceptions to this tendency are the Superla 165/170” and Jasber 180/185” waxes (e and h, Fig. 2) and the 140/145” ex Assam and the 56/58O German Zeitz waxes (fand j, Fig. 1). The additional peaks in the paraffin wax traces may be due to the crystalline transition orthorhombic + hexagonal which Ludwig 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 and paraffin waxes. At the higher temperatures all the paraffin waxes showed broad diffuse peaks which returned to baseline before 460”. In contrast, a sharp peak at 475-480” is characteristic of all the microcrystalline and polyethylene waxes which we have examined. This peak may be used to identify the presence of a microcrystalline or polyethylene wax in a mixture and also to give a quantitative estimation of the amount present; thus Table I shows the results obtained by measuring the area of this peak and relating it to the amount of microwax C700 in an artificial mixture of this microwax and the paraffin wax 135/140” ex Stanlow Refinery. The DTA trace of the mixture containing 50.0 % of microwax is reproduced in Fig. 3.
421
Characterization
and analysis of waxes by differential thermal analysis
I
0
I
I
loo
200
I 400
I 300
T-UN.
I so0
1
.C
curve of 1: 1 mixture of microwax C23 and par& wax 135/140 ex Stanlow Refinery. The shaded area gives a measure of the amount of microwax present (see Table 1). FIG.
3.-DTA
TABLEI.-TYPICAL RESULTSOBTAINED ANALYSIS AND
OF
MIXTURJZS
PARAFFIN
WAX
OF
MICROWAX
135140 ex
IN
THE
000
STBUW
REFINERY
Microwax present, %
Microwax found by measuring the area of the peak at 475”. %
71.9 50.0 47.2 19.2
67.3 53.9 51.6 15.6
Tamw~roture,
=C
4.-DTA curves of waxes. a Hoechst Wax L; b, Hoechst Wax OM ; c. Candelilla Wax; d, Beeswax; e, Carnauba Flake. FIG.
423
424
B. R. C-L
and B. ROBINSON
To provide a comparison the DTA traces of some other waxes are included (Fig. 4). These include the natural waxes Beeswax, Candelilla and Carnauba Flake and the synthetic Hoechst waxes L and OM. These results are preliminary; a full evaluation of the limitations of this method of analysing wax mixtures will be carried out when we have finished a programme of work designed to define the limitations of DTA as a quantitative method; factors to be taken into account will include variations in the size and thermal conductivity of the samples, heating rate, crucible design and methods of packing. EXPERIMENTAL 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 of which rested OD chromel-ahnnel thermocouples; the cups were supported in an inconel block. Differentialtemperature was plotted against block temperature on an Aminco X-Y recorder. All runs were carried out at a heating rate of 8O/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 as possible of the same weight. Acknowle&ements-We wish to acknowledge the generosity of the American Instrument Co. in providing the DTA equipment on loan, andalso theexperimentalassistancegiven by Mr. P. Stevenson, who carried out many of the runs. Zusammenfassung-Die Charakterisierung von Wachsen durch Differentialthermoanalyse wird beschrieben. Ein endothermer Peak bei 475-480” ist charakteristisch fiir mikrokristalline und Polyiithylenwachse; Messung seiner Fliiche bietet eine Methode zur Bestimmung dieser Wachse in Gemischen. R&&---On d&it la caracterisation de tires par analyse thermique differentielle. Un pit endothermique a 475-480” est caract6ristique de tires microcristallines et poly&hyl&iques et la mesure de son aire foumit une mtthode d’estimation de ces tires dam des melanges. REFERENCES 1. 2. 3. 4. 5.
S. W. Ferris, Tech. Assoc., Paper Pu& Ind., Spec. Tech. Assoc. Publ., 1963, 2, 1. R. C. Fox, ibid. 1963, 2, 160. P. R. Templin, ibid. 1963, 2, 51. F. J. Ludwig, Anal. Chem., 1965,37, 1737. J. Lange and H. Jochinke, Fette Seifen Anstrichmittel, 1965, 67, 89.