Effect of surface modification of fly ash on the mechanical, thermal, electrical and morphological properties of polyetheretherketone composites

doi:10.1016/j.msea.2011.01.026

Materials Science and Engineering: A

Volume 528, Issues 13–14, 25 May 2011, Pages 4277-4286

https://doi.org/10.1016/j.msea.2011.01.026 Get rights and content

Abstract

Poly (ether ether ketone) (PEEK)/fly ash (FA) composites were prepared using melt blending technique. To improve the interfacial interaction of fly ash with the PEEK matrix, fly ash was chemically modified with calcium hydroxide, at different concentration. Various characterization studies like dynamic mechanical thermal analysis (DMTA), modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM) have been carried out to evaluate the storage modulus, tan δ, crystallinity, and morphology in the composites. SEM micrographs showed more uniform dispersion and interaction in the modified composites than unmodified counterpart. Surface modified fly ash improved the interfacial adhesion between fly ash and PEEK which is confirmed also through improved mechanical strength. The dynamic modulus of PEEK composites exhibited over 133% increment at 100–250 °C, indicating improvement of elevated temperature mechanical properties. The modified fly ash reinforcements also showed improvement in glass-transition and crystallization temperature.

Research highlights

► Preparation of high performance poly (ether ether ketone) (PEEK)/fly ash (FA) composites. ► Characterization studies like DMTA, MDSC, FTIR and SEM have been carried out. ► Addition of modified FA, decrease T_c by 58 °C, due to the hindrance in PEEK molecular mobility during the cooling crystallization process. ► Modified fly ash filled PEEK composites exhibit higher tensile strength and modulus than the unmodified ones.

Introduction

Although the use of fillers in plastics industry has been known for several decades, there is still a huge demand in academia and industry for the development of high performance composite materials with desired attributes. In particular, the growing need for high tech products, accelerate the research in advanced composites, which demand extensive knowledge of all the factors that determine the final properties in the polymeric composite materials. It has been reported that the decreasing filler dimension and increasing filler content will significantly improve the specific area of the filler, which in turn would greatly and effectively improve the transfer of the load between the fillers and polymer matrix. Particle filled polymer composites have become attractive because of their wider applications and low cost. Incorporation of inorganic mineral fillers into thermoplastic resin improves various physical properties of the materials such as mechanical strength, modulus and heat deflection temperature. The properties of the composites depend upon the characteristics of components, composition, structure and interfacial interactions. The latter factor is greatly affected by the size of the interface and the strength of the interaction. Surface treatments with different modifiers such as stearic acid, silane and titanate coupling agents have been reported to improve the interface and strength of the interaction between the filler and the matrix [1], [2], [3], [4], [5], [6], [7], [8], [9].

Performance of composites depends not only on the characteristics of the filler, but also on the dispersion of filler and polymer–filler interactions, and more specifically on the properties and thickness of interphase between polymer and filler [10], [11], [12]. It is well known that the final performance of the composites depend upon the capabilities of the interphase to transmit the stress from matrix to filler. The particle agglomerates have to be broken down into smaller parts called aggregates to increase the dispersion characteristics. During compounding, mechanical shear induces dispersion of the filler within the matrix. The mechanism for dispersion has been extensively studied by various researchers [13], [14].

Fly ash, a waste material, obtained in huge quantities from thermal power plant as by-product of the burning of pulverized coal. This thermal waste has received considerable attention in the recent years as an additive component in the polymer composites. Fly ash is fine and powdery in nature with the particles essentially spherical in nature [15], [16]. Fly ash filled polymer matrix composites have been studied by various workers [17], [18], [19], [20] to improve the bulk properties of the matrix polymer predominately and have driven high volume applications.

PEEK is a high performance semicrystalline polymer having outstanding thermal stability, wear resistance, mechanical properties, and excellent resistance to chemicals. It has high melting (T_m), glass transition (T_g) and wide service temperature. It can be processed by conventional methods such as injection molding, extrusion, compression molding and powder coating techniques. Therefore, PEEK and its composites have been reported to be extensively used in aerospace, automotive, structural, high temperature wiring, tribology, and biomedical applications [21], [22], [23]. Several studies on PEEK filled with micron size particles such as aluminium nitride (AlN) [24], [25], aluminium oxide (Al₂O₃) [26], CaCO₃ [27], and hydroxyapatite (HA) have been extensively investigated [28].

In the present study, fly ash particles were introduced into PEEK compound, due to prances of hydroxyl group on the surface, and calcium hydroxide was chosen as a chemical modifier to improve the interaction between PEEK and fly ash composites. The aim of the work is to optimize the concentration of the surface modified fly ash to achieve improved performance characteristics with controlled morphology.

Section snippets

Materials

The PEEK granules (grade 5300) were obtained from M/s Gharda Chemicals, Ltd., Panoli, Gujarat, India. Fly ash of average particle size 53 μm was obtained from M/s Kuradi thermal power Nagpur, India. Calcium hydroxide used as surface modifier, was supplied by M/s Aroma chemical agencies, Mumbai, India.

Surface modification of fly ash

A solution of 10 g calcium hydroxide (Ca(OH)₂) in 100 ml of water was prepared with continuous stirring for 5 min at 80 ± 5 °C, to obtain 10 wt% solution. 100 g of fly ash was then added into the solution

Effect of fly ash concentration on the mechanical properties of PEEK composites

Fig. 2 shows the mechanical properties of unmodified fly ash filled PEEK composites at varying concentration (0–30%). It is observed that with the increase in concentration of fly ash up to 20 wt%, there is an increase in the tensile strength beyond which it decreases. This behavior is probably due to counterbalance of two factors; increase in the filler content in a polymer composite results in increase in effective surface fracture energy, size of voids and agglomeration of filler particles.

Conclusion

1.
The Ca(OH)₂ modified fly ash filled PEEK composites shows better interaction in fly ash/PEEK matrix more uniform filler dispersion, and it appears the smaller inter-planer spacing of the PEEK crystalline phase. However, the unmodified fly ash filled PEEK composites do not reveal this effect.
2.
The inclusion of the modified fly ash did not alter much the T_m values of the resulting PEEK composites, but decrease T_c by 58 °C, due to the hindrance in the PEEK molecular mobility during the cooling

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Citation Excerpt :
Merwe used sodium dodecylsulfate to modify the surface of FA to improve its dispersibility in concrete [21]. Moreover, Parvaiz considered that the FA modified by 10% Ca(OH)2 solution was used to better the strength by improving the interface between FA particles and hardened cement [22]. Then, Donatello immersed mortar with high-volume FA into HCl and Na2SO4 solutions to boost the compressive strength by crystallization of the hydrated products [23].
This study aimed to introduce fluidized bed reactor-vapor deposition (FBR-VD) into the modification of fly ash
(FA) using the activators of HCl (HC), H₂SO₄ (HS), NaOH (NH), Na₂SO₄ (NS), and NaCl (NC) to reveal the modification mechanism and hydration process of FA. The simple and effective modification device is innovatively combined with building materials to promote the utilization of FA, and the chemical reagents of HC and HS are firstly used in constructive materials to modify FA. The fluidity, compressive strength and the risk of Cl⁻ presence were analyzed. The hydration process was conducted by the hydration heat, chemical shrinkage, selective chemical dissolution method, scanning electron microscopy (SEM) and thermogravimetric-differential scanning calorimetry (TG-DSC). The modification mechanism was investigated by X-ray photoelectron spectroscopy (XPS) and fourier transform infrared spectroscopy (FTIR). The results demonstrate that HC can significantly improve the fluidity of the FA-cement paste and modifiers can increase the intensity at different ages except for NS. The Cl⁻ in the modifiers does not affect the safety of concrete. The modifiers of NC, HC, NH, and HS can enhance the early hydration rate and the degree of hydration of FA to increase the compressive strength of the FA-cement paste. Modifiers can promote the cleavage of the Si–O bond and the Al–O bond of the network structure in FA, effectively activating the pozzolanic activity of FA.

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Effect of surface modification of fly ash on the mechanical, thermal, electrical and morphological properties of polyetheretherketone composites

Abstract

Research highlights

Introduction

Section snippets

Materials

Surface modification of fly ash

Effect of fly ash concentration on the mechanical properties of PEEK composites

Conclusion

J. Appl. Polym. Sci.

Mech. Mater.

Comp. Sci. Technol.

Int. J. Solids Struct.

J. Appl. Mech.

Int. J. Mech. Sci.

J. Mater. Sci.

Polymer

J. Mech. Phys. Solids

Compos. Part A: Appl. Sci. Manuf.

J. Appl. Polym. Scil.

J. Mater. Sci.

J. Appl. Mech.

Handbook of Fillers and Reinforcement for Plastic

J. Appl. Polym. Sci.

J. Appl. Polym. Sci.

Rubber Compos.

J. Appl. Polym. Sci.

J. Appl. Polym. Sci.