Preparation and Characteristics of Polystyrene / Attapulgite Composites Via In-siu Suspension Polymerization

A series of polystyrene/attapulgite composites were synthesized through suspension polymerization. The composites were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and X-ray diffraction. FTIR results show that there was no significant change in the peak positions and the peak intensity for polystyrene/attapulgite composites compared to the pure polystyrene. There is a rise in thermal stability of composites compared to pure polystyrene. Attapulgite acts as an effective thermal barrier and thereby hinders the degradtion of polystyrene.


Introduction
Polymer-matrix compoites have attracted much attention of researchers due to creation of materials with improved physical and chemical properties.A number of studies have been performed aimed at improving the thermal stability and mechanical properites of polystyrene (PS) by compounding it with organic or inorganic particles [1][2][3], such as multi-wall carbon [4], clay [5] and graphene [6].For example, P. Pereira et.al [7] compared the impact of fullerenes and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on the thermal stability of melt processed polystyrene, and reported that the PS-PCBM have higher thermal than the corresponding PS-C 60 .A. Krishnan et.al. [8] investigated the effect of cellulose nanofibers on the mechanical and morphological properties of polypropylene/polystyrene blend.
Comparatively, the polymer-modified clay minerals possess more excellent dispersibility and good property than others.Attapulgite (ATP), natural Mg-Al silicate clay mineral with one-dimension crystal morphology, have recently received a great deal of attention.Attapulgite play important role in modifying the desirable properties of polymers and reducing the costing of their composites.To ensure interfacial interactions of the layered silicate with other polymer matrices, the layered surface must be converted to an organophilic surface.Organic attapulgite is one of the most important clay.Polymer/organic attapulgite composites have been attracting great interest because of their improved properties.
In this work, the attapulgites were used for the polystyrene-based composites via suspension polymerization.The effects of attapulgite loading on the properites of the polystyrene and the thermal degradation were confirmed by FTIR, XRD and TGA.

2.1Materials
The monomer of styrene and dibenzoly peroxide (BPO) as a free radical initiator were purchased from aladdin Co. Ltd. (China).Poly(vinyl pyrrolidone) (PVP) was used as stabilizing agent.The attapulgite which is one of natural fibrillar minerals was supplied by the Jiuchuan Nano-material Technology Co. Ltd.

2.2Specimens Preparation
A series of polystyrene/attapulgite composites were synthesized through suspension polymerization.Attapulgite concentrations were 1, 3, and 5 wt% of monomer total weight.0.3g of BPO, 0.14g attapulgite, and styrene were placed in the three-necked flask.The attapugite were dispersed by sonication for 10min.Then 20ml 1.5% PVP and deionized water were added to three-necked flask.under constant stirring at 90 o C for 2h.Finally, PS/attapulgite particles were collected on a filter, washed with deionized water and dried in a in vacuum drying chamber at 60 o C.

2.3Characterizations
Fourier-transform infra-red (FTIR) spectroscopy has been used to monitor the chemical reactions.For the infrared measurement a small portion of the samples were grind to a fine powder, mixed with potassium bromide (KBr) powder and pressed into a pellet by hand press.FTIR were recorded by nicolet NEXUS-670 IR spectrometer in the wavelength range of 4000-400cm -1 .
X-ray diffraction patterns were recorded in XD-6 X-ray diffractometer (China).The length and width of all test samples are 20mm and 15mm, respectively.The wavelength of the monochromated X-ray from Cu KĮ radiation is 0.154056nm.The scanning 2ș range was 10-60° with a scanning rate of 2°/min.Thermogravimetric analysis (TGA) was carried out on a HTC-1 TG (China).The mass of each specimen was about 6 mg.Thermogravimetry analysis curves were recorded in the course of heating from 25 to 500 at a heating rate of 10 /min.

3.1Chemical Structure of Polystyrene/Attapulgite Composites
FTIR spectral analysis was performed to confirm the chemical structure of polystyrene and polystyrene/attapulgite composites.The FTIR spectra of polystyrene and polystyrene/attapulgite composites were shown in Fig. 1.The absorption peak at about 3500 cm -1 was assighed to the absorption of water inside the PS.The peak at about 3000 cm -1 corresponding to the asymmetrical and symmetrical stretching vibrations of -CH 2 could be observed.The peak at 1500 cm -1 was assined to aromatic C-H stretching.There was no significant change in the peak positions and the peak intensity for polystyrene/attapulgite composites, indicating that the composite have the same structural properties.

3.2X-ray Diffraction Analysis
Fig. 2 shows the XRD patterns of polystyrene and polystyrene/attapulgite composites.Both polystyrene and polystyrene/attapulgite composites exhibit a broad diffraction peak and its location does not change..It can be seen that the reflexes associated with attapulgite are absent in XRD patterns of composite.This is due to that the concentration of attapulgite in the studied composites is inadequate for the occurrence or the weak aggregation of attapulgite.

3.3Thermal Degradation of Composites
Fig. 3 shows the TG curves from the thermal degradation of the effect of attapulgite on the decompoition behavior of polystyrene.Both polystyrene and polystyrene/attapulgite composites decomposed in a one step process.The TGA curves showed that polystyrene and composites undergo massive thermal degradation after 320 .The TGA curve profile of the composites shifted towards a higher temperature compared to pure polystyrene.There is a rise in thermal stability of composites compared to pure polystyrene.Attapulgite acts as an effective thermal barrier and thereby hinders the degradtion of polystyrene.Fig. 4 shows the DTA of TGA, which gives the peak temperature at which the macimum weight loss occurred.The DTA curve shows a single prominent rate of weight loss peak, which indicated that the thermal degradation consisted of one main weight loss step.

Conclusions
In this work, polystyrene and polystyrene/attapulgite composites were prepared through in situ suspension polymerization.The polystyrene/attapulgite composites were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, and X-ray diffraction.FTIR results show that there was no significant change in the peak positions and the peak intensity for polystyrene/attapulgite composites compared to the pure polystyrene.TGA results show that the attapulgite enhanced thermal properties for polystyrene.Attapulgite acts as an effective thermal barrier and thereby hinders the degradtion of polystyrene.