Influence of the Alkane Molar Distribution on the Physical Properties of Synthetic Waxes

Abstract

The purpose of this paper is to compare the structure and the mechanical properties of several model mixtures exclusively constituted of pure linear alkanes so as to better understand the conditions in which disorder appears within real systems. The molar distribution of all the studied mixtures is of "normal logarithmic type", and the only statistical parameter varying from one mixture to the other is the standard deviation (σ) of the distribution. This work was carried out by means of X-ray diffraction, differential scanning calorimetry (DSC), and dynamical mechanical analysis (DMA) according to temperature. The obtained results show that the number of crystallized phases increases with the standard deviation and that the structural evolution versus temperature of the mixtures also depends on this statistical parameter. With regard to the mechanical properties, the results of the dynamic mechanical analyses show that the storage modulus (E 0 ) and the loss factor (tan δ) are also affected by the standard deviation of the distribution.

Effect of the amount and the composition of precipitated n-alkanes on the yield stress of wax-decane gels

“…With known XRD determined average carbon number (n c ) and the real average carbon number (  ) of precipitated C n , the conformation disorder in wax crystals was revealed using c nn     (Chevallier et al, 2000;Petitjean et al, 2010). As shown in Table 3 and Fig.…”

“…Furthermore, no quantitative structural parameters were provided in previous work to investigate the effect of co-crystallization. (Guo et al, 2004;Senra et al, 2008Senra et al, , 2009 To interpret the effect of the composition on the structural parameters (a, b, c) of wax crystal, the XRD technique has been widely used (Briard et al, 2004;Chevallier et al, , 2000Petitjean et al, 2010). When the precipitated C n is in the shape of orthorhombic, the crystalline lattice c-parameter detected by XRD can provide the information on the conformation disorder of n-alkanes (Dirand et al, 2002).…”

“…Comparing this n c with the real average carbon number (  ) of precipitated C n based on carbon number distribution, the extent of conformation disorder of C n can be obtained. Petitjean et al (2010) used synthetic waxes of different n-alkane polydispersity to investigate the relationship between C n molecule conformation disorder and the mechanical property of synthetic waxes. It was found that the storage module was drastically decreased when the extent of conformation disorder of C n increases.…”

“…Instead, the average carbon numbers of the synthetic waxes were used to be compared with the XRD determined average carbon number (n c ) of precipitated C n . Petitjean et al (2010) provided a useful method to correlate the mechanical strength of wax-oil gel with the composition of precipitated C n except that the experimental procedure needs to be completed.…”

“…The XRD method can adequately describe the structural parameters of precipitated C n . However, the previous works were limited in mono-disperse or binary C n in decane solutions, and some limitations exist in the experimental procedure provided by Petitjean et al (2010). This work added the centrifugation and HTGC method into the experimental procedure to obtain the real average carbon number (  ) of precipitated C n .…”