Influence of Organo-Sepiolite on the Morphological, Mechanical, and Rheological Properties of PP/ABS Blends

To improve the poor impact toughness of polypropylene (PP), organo-sepiolite (O-Sep) filled 80/20 (w/w) polypropylene/poly(acrylonitrile-butadiene-styrene) (PP/ABS) nanocomposites were fabricated. The contents of O-Sep were correlated with the morphological, mechanical, and rheological behavior of PP/ABS/O-Sep blends. Scanning electron microscopy (SEM) was applied to study the morphology and thermogravimetric analysis (TGA) was applied to study the thermal stability. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were applied to study the crystallinity. The obtained results show that O-Sep enhanced the dispersion of ABS in the PP matrix and increased the crystallinity of blends. The rheological results show that O-Sep could increase the viscosity, storage modulus, and loss modulus of blends. Moreover, the mechanical behavior shows that O-Sep (at proper content) simultaneously increased the tensile modulus, flexural modulus, and impact strength of PP/ABS/O-Sep blends.


Introduction
Due to its low density, good elongation, high thermal stability, and good solvent resistance, polypropylene (PP) has become one of the most popular engineering plastics. However, low temperature brittleness and poor impact resistance restrict its applicability. Among all strategies for PP toughening, the introduction of a β-nucleating agent has been demonstrated to be the most reliable strategy [1][2][3][4][5][6][7][8]. Nowadays, due to the low cost, simple processing, and their non-toxic, macromolecular β-nucleating agents (such as polystyrene (PS), acrylonitrile-butadiene-styrene graft copolymer (ABS), or thermo-plastic phenolic resin) have been reported to have higher β-nucleating efficiency compared with low molecular weight organic β-nucleating agents. Moreover, benzene rings in the macromolecular structure may serve as a growth center for crystals [9][10][11][12][13][14][15][16][17][18]. Due to the advantages it offers, polymer blending technology has become one of the major strategies for the research and development of polymer materials in the past decade [19][20][21][22][23]. In a blend, the less viscous components form the continuous phase and the contents of dispersed phase determine the final morphology and thermo-mechanical properties. According to the mutual solubility and melt viscosity, polymers can be divided into compatible and incompatible polymers. Therefore, a physical or chemical modification of commodity is commonly applied in polymer blending technology.
ABS resin has a two-phase structure, has been demonstrated to perform like a typical rubber and improves the impact resistance of PP. ABS resin has also been reported to induce β-crystallization in Table 1.

Measurements and Characterizations
A FTIR spectrometer (Nicolet IS50, Thermo Fisher Scientific Inc., Waltham, MA, USA) was applied to characterize Sep, CG-570, and O-Sep, and the test resolution was 4 cm −1 , the number of scans was 32, and the test range was 400-4000 cm −1 . A FEI Quanta 250 FEG field-emission scanning electron micro-scope (SEM) (Thermo Fisher Scientific Inc., Waltham, MA, USA) under high vacuum at a voltage of 20 kV was applied to observe the morphologies of all testing samples, all testing samples were cryofractured with the direction parallel to the injection molding direction and coated with a thin layer of Pt. A TG 219 F3 thermal analyzer (Netzsch Instruments Co., Ltd., Hanau, Germany) was applied at a constant scanning rate of 10 • C/min under nitrogen at temperatures ranging from 50 to 600 • C to evaluate the thermal stability of all testing materials. DSC 214 (Netzsch Instruments, Co., Ltd., Hanau, Germany) at a heating rate of 10 • C/min was applied to study the crystallization of all testing samples. The samples were heated from 30 to 230 • C and held at this temperature for 5 min and then cooled to 30 • C at a rate of 10 • C/min. This was repeated to obtain a second heating scan. XRD (D/MAX2500, Rigaku Corporation, Tokyo, Japan) with Cu Kα radiation (λ = 1.54 Å) over the range of 5 • -35 • at a scanning rate of 2 • /min was applied to study the crystalline structure of Sep and the blends, and the measurement geometry was Bragg-Brentano geometry, the voltage was 40 kV, the filament current was 40 mA. CMT6104 (MTS, Beijing, China) was applied to study the tensile performance testing (sample size: 75 mm × 5 mm × 1.88 mm) and bending performance testing (sample size: 64 mm × 10 mm ×

Modification of Sep
To improve the dispersion of Sep in the PP/ABS blends, Sep was modified with diluted HCl and CG-570 to prepare O-Sep. As shown in the FTIR curves in Figure 1a, O-Sep has an asymmetric stretching vibration peak of an alkane-CH bond at 2946 cm −1 [52] and a stretching vibration peak of carbonyl C=O at 1718 cm −1 . The strong and wide absorption band at 1093 cm −1 shows the stretching vibration absorption peak of the Si-O-Si bond. The stretching vibration peak of Si-O bond at 910 cm −1 indicated that Si-OH reacted with Sep. FTIR demonstrated that CG570 successfully modified Sep. The further TG results ( Figure 1b) were consistent with the FTIR results, and neither Sep nor O-Sep had hydroxyl water and coordination water (no obvious peak at 3500-3600 cm −1 ), Sep and O-Sep are very stable below 433.9 • C. After organic modification with CG-570, the mass loss of Sep increased, which further indicated that Sep has been modified with CG-570 successfully.

Modification of Sep
To improve the dispersion of Sep in the PP/ABS blends, Sep was modified with diluted HCl and CG-570 to prepare O-Sep. As shown in the FTIR curves in Figure 1a

Morphology of Blends
A β-nucleating agent-based method has been demonstrated to be the most reliable strategy for PP toughening, and the dispersibility of the β-nucleating agent is key during this procedure. As shown in Figure 2a

Morphology of Blends
A β-nucleating agent-based method has been demonstrated to be the most reliable strategy for PP toughening, and the dispersibility of the β-nucleating agent is key during this procedure. As shown in Figure 2a Figure 2c-f, the O-Sep is 1 wt%, 3 wt%, 5 wt%, and 7 wt%, respectively. When introducing O-Sep into PP/ABS blends, the aggregation of ABS in the PP matrix gradually decreased, and the interface of the two-phase gradually blurred. This indicates that the introduction of O-Sep into the blends improved the dispersion of ABS in the PP matrix. In summary, the phase morphologies in the SEM images demonstrate that O-Sep has good compatibility with PP/ABS blends and the introduced O-Sep may serve as a special compatibilizer for PP/ABS blends.

Mechanical Properties
To investigate the influences of β-nucleating and O-Sep on the mechanical properties of PP, the influences of ABS on the mechanical properties of PP were investigated first. Then, the influences of O-Sep on the mechanical properties of PP/ABS blends were investigated. Table 2  Bonda and co-workers have reported that the tensile strength of PP and PP/ABS (20%) is 29.0 and 31.8 MPa respectively [26]. In our experiments, the tensile strength of PP and PP/ABS (20%) is 36.3 and 38.6 MPa respectively. Liu and co-workers have demonstrated that ABS and nano-ZnO could toughen PP. For instance, the impact strength of PP and PP/ABS/ZnO is 3.31 and 10.29 kJ/m 2 respectively in their experiments [24]. In our experiments, the impact strength of PP, PP/ABS, and PP/ABS/O-Sep5 is 4.54, 5.50, and 6.39 kJ/m 2 respectively.
A β-nucleating agent-based method has been demonstrated to be the most reliable strategy for PP toughening, and the dispersibility of the β-nucleating agent is key during this procedure. As shown in Figure 2a-f, the SEM images represent PP and PP/ABS/O-Sep with various O-Sep contents. For pure PP (Figure 2a), the SEM image shows homogenous phase and has no aggregation. For nanocomposite in the absence of O-Sep (Figure 2b), the SEM image shows that ABS microspheres dispersed in the PP matrix, showing a clear interface of both phases. In Figure 2c-f, the O-Sep is 1 wt%, 3 wt%, 5 wt%, and 7 wt%, respectively. When introducing O-Sep into PP/ABS blends, the aggregation of ABS in the PP matrix gradually decreased, and the interface of the two-phase gradually blurred. This indicates that the introduction of O-Sep into the blends improved the dispersion of ABS in the PP matrix. In summary, the phase morphologies in the SEM images demonstrate that O-Sep has good compatibility with PP/ABS blends and the introduced O-Sep may serve as a special compatibilizer for PP/ABS blends.  In short, adding O-Sep to the blends achieved better mechanical properties when compared with pure PP and PP/ABS blends. O-Sep may serve as a compatibilizer and help to improve interfacial adhesion, which is also supported by the results of SEM images shown in Figure 2. When sufficient O-Sep has been added, the dispersion of O-Sep into the PP/ABS matrix will become difficult, and the corresponding mechanical properties will begin to decrease [49].

Rheological Properties
The rheological behavior of polymers or polymer-based nanocomposites plays a vital role in their microstructure and processability [54,55]. It has been demonstrated that incorporating nanoparticles into a neat polymer could change the rheological properties of polymer matrix [56,57].

Rheological Properties
The rheological behavior of polymers or polymer-based nanocomposites plays a vital role in their microstructure and processability [54,55]. It has been demonstrated that incorporating nanoparticles into a neat polymer could change the rheological properties of polymer matrix [56,57]. Figure 6a

Rheological Properties
The rheological behavior of polymers or polymer-based nanocomposites plays a vital role in their microstructure and processability [54,55]. It has been demonstrated that incorporating nanoparticles into a neat polymer could change the rheological properties of polymer matrix [56,57].

Conclusions
In

Conclusions
In summary, PP/ABS/O-Sep nanocomposites (with various O-Sep contents) were prepared and the effects of O-Sep on the thermo-mechanical properties of nanocomposites have been systematically investigated. The results indicate that the toughness of PP can be improved by introducing both ABS and O-Sep. SEM images indicated improved dispersion of ABS in PP matrix by introducing O-Sep. The thermo-mechanical properties showed that not only the toughness of PP/ABS was enhanced by introducing O-Sep but also its crystallization temperature. Furthermore, the PP/ABS/O-Sep nanocomposites showed increased viscosity and modulus compared with PP/ABS blend and pure PP, and O-Sep acted as a reinforced filler. This work provides a new strategy to improve the PP/ABS blend system by introducing O-Sep as a nucleating agent and compatibilizer, and may provide a route for the toughening of PP.