Stearic acid modified tourmaline powder had been investigated to improve the compatibility and dispersed stability between tourmaline and polymer matrix. The experimental results indicated that the activation index was 100% and contact angle reached 120° when the ratio of the ore slurry is 5:50, the dosage of stearic acid and p-toluenesulfonic acid is 10% and 0.5% (of tourmaline powder’s quantity) respectively with reaction at 80°C for 6.0 h, and the modified tourmaline exhibited an excellent hydrophobic property. The introduction of stearic groups reduced the reunion of tourmaline particles clearly and improved the dispersivity in polymers, and the amount of negative ions released of modified tourmaline increased obviously for both modified tourmaline powders and its composite with polyamide-66 compared to the unmodified tourmaline. Moreover, the structure of modified tourmaline was also characterized by means of Fourier Transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, scanning electron microscope.
Tourmaline is a particular mineral and attracting widespread attentions for its piezoelectric and pyroelectric characteristics since which was discovered by E. Rieche [
Generally, tourmaline powders and polymers are in poor compatibility due to their different surface properties. The poor dispersity of tourmaline, especially in a non-polar polymer matrix, can always reduce the mechanical properties, and thus leading to low overall performance of the material [
In this study, we report our investigation on the reactivity between tourmaline powders and stearic acid, in which the activation index and contact angle are the two major experimental parameters that we concerned on, and the tourmaline/PA-66 composites combined with a polar polymer polyamide-66. The structure of modified tourmaline was characterized, and the amounts of negative ions released by modified tourmaline powders and its composite have been measured quantitatively.
Tourmaline powder with diameters of d50 1.75 mm and d97 5.23 mm (purity 98%) was purchased from Yanxin Mineral Company Limited, Hebei, China; stearic acid (analytical reagent) was obtained from West Long Chemical Company; and liquid paraffin (chemical pure), ethanol (analytical reagent), acetone (analytical reagent), toluene (analytical reagent) and p-toluenesulfonic acid (analytical reagent) were purchased from Beijing Chemical Reagent Factory, and polyamide-66 was purchased from Pindingshan Shenma Engineering Plastics Company Limited.
The testing devices included a Perkin Elmer Spectrum 100 Fourier transform infrared (FTIR) spectrometer (Shanghai Company) and a Rigaku D/max-rA 12 kw X-ray diffractometer (XRD) (Japan). Scanning electron microscope (SEM) images were observed on a Hitachi Model S-450 scanning electron microscope, and the DSA100M optical measurement (Zhongchen Digital Technology & Instrument Company, Shanghai) was used for the measurements of the contact angles. Thermal gravimetric analysis (TGA) was analyzed with Q500 Thermogravimetric Analyser (TA instrument Company, American); And the amount of negative ions released were measured on the AIC1000 negative ion concentration tester (Alphalab Company, American).
In a 100 ml three-neck flask, 5 g of super-fine tourmaline powder and stearic acid in 50 ml of toluene was stirred adequately, then p-toluenesulfonic acid was added into flask, reacted at 80˚C for 5 h. The samples were separated by centrifugation, washed three times with ethanol and acetone, and finally dried and ground prior to characterization.
The sample was pressed into a circle using a press, and distilled water was then dripped onto the surface of the sample to evaluate the contact angle using optical measurements. Each value was averaged over three tests.
The activation index of the modified tourmaline was determined according to the HG/T2567 standard (former Ministry of Chemical Industry). In a 100 ml beaker, 1.0 g of modified tourmaline (M0) in 50 ml of water was stirred for 5 min and allowed to stand statically for 5 h. The turbid solution in the middle of the beaker turned clear, and the powders floating on top of the solution were collected, dried and weighed as M1. The activation index was calculated as follows:
The modification effect of tourmaline powder under various conditions such as the quantity of stearic acid and p-toluenesulfonic acid, reaction temperature and time were studied by focusing on the experimental parameters of the activation index and contact angle.
The influence of the amount of stearic acid is shown in
The influence of the reaction temperature is displayed in
The influence of reaction time on the modification of tourmaline is plotted in
Effect of weight ratios of stearic acid to tourmaline
Effect of temperature
The influence of the amount of p-toluenesulfonic acid on the modification of tourmaline is presented in
The mass ratios of tourmaline to solvent also have impact on the modification of tourmaline, which is illustrated in
The structure of modified tourmaline was characterized by IR spectra, XRD analysis, SEM images and so on.
Effect of reaction time
Effect of the amount of p-toluenesulfonic acid
The influence of weight ratios of tourmaline to solvent
IR spectra of unmodified (a) and modified (b) tourmaline
band exhibits a red shift because of the electric effect of the metal ions on the surface of tourmaline. Other peaks (e.g., the B-O and Si-O bands) are also red shifted for a few wave numbers and broadened. These results indicate that stearic groups were introduced onto the surface of the tourmaline by the reaction of stearic acid with tourmaline powder (Equation (1)), and therefore the hydrophobic properties of tourmaline were improved.
The XRD patterns of unmodified and modified tourmaline are shown in
The SEM images of unmodified and modified tourmaline are presented in
XRD spectra of unmodified (a) and modified (b) tourmaline
SEM images of unmodified (a) and modified (b) tourmaline
The TGA curves of unmodified (a) and modified (b) tourmaline
The amount of negative ions released from the unmodified and modified tourmaline was listed in
In order to evaluate the dispersancy of modified tourmaline in a polymer, the composites of modified tourmaline and unmodified tourmaline with polyamide-66 (PA-66) were prepared, and characterized by SEM images and by the detection of the release of negative ions.
1) The preparation of tourmaline/PA-66 composites
Tourmaline (5% of PA-66 dosage) was added to a flask that contained PA-66 dissolved in dimethyl sulfoxide (DMSO) and stirred for 40 min at 170˚C. The mixture was cooled and poured into the distilled water with stirred quickly, then filtrated and washed three times with distilled water, dried to get the tourmaline/PA-66 composite.
2) SEM analysis of tourmaline/PA-66 composites
3) The examination of amount of negative ions released of tourmaline/PA-66 composites
The amount of negative ions released by tourmaline/PA-66 composites is shown in
The activation index of modified tourmaline powder can reach 100% when tourmaline-to-solvent mass ratios is
The SEM images of unmodified tourmaline/PA-66 (a) and modified tourmaline/PA-66 (b) composites
. The amount of negative ions released by unmodified and modified tourmaline
Sample | The amount of negative ions (ions/cm3) |
---|---|
Tourmaline | 320 |
Modified tourmaline | 860 |
. The amount of negative ions released by composites of tourmaline/PA-66 and modified tourmaline/PA-66
Composites | The amount of negative ions (ions/cm3) |
---|---|
5% tourmaline/PA-66 | 300 |
5% modified tourmaline/PA-66 | 500 |
5:50, the dosage of stearic acid and p-toluenesulfonic acid are 10% and 0.5% (of tourmaline powder’s quantity) respectively, at 80˚C for 6.0 h. The contact angle of the modified tourmaline is 120˚, which exhibits excellent hydrophobic properties for the modified tourmaline. The experimental results indicated that the stearic groups were introduced onto the surface of tourmaline by transesterification of the hydroxyl groups at the surface of the tourmaline particles with stearic acid, which improved the hydrophobic properties of tourmaline surface while keeping its crystal configuration unchanged, and reduced the reunion of tourmaline particles clearly and improved the dispersivity in polymers. And the amount of negative ions released by modified tourmaline increased obviously for both modified tourmaline powders and its composite with PA-66 compared to the unmodified tourmaline. The results offered an importance to prepare functional tourmaline composites.
This work is supported by the National Natural Science Foundation of China (No. 51072187, No. 51372233).