Preparation And Properties Of Poly (Ether Ether Ketone) (PEEK)/Organic Modified Montmorillonite (OMMT) Composites

At present, polymer/montmorillonite nanocomposites have become a research hotspot of polymer nanocomposites. Because the inorganic phase with nano-size can uniformly dispersed.in polymer matrix, a small amount of montmorillonite obviously improve properties of polymer matrix, such as modulus, strength, barrier properties, thermal stability, and optical properties. With the development and application of commercial products, the researchers focus on the novel montmorillonite nanocomposites.Poly (ether ether ketone) (PEEK) has excellent rigidity, radiation resistance, fatigue resistance, creep resistance, abrasion resistance, fire-retardant features, etc. Therefore, it has been successfully applicated in the aviation, aerospace, nuclear energy, information, communication, electronic telecommunications, petrochemical, machinery manufacturing, transportation and other high-tech fields, followed by the replacement of traditional products. Although excellent properties is more important than cost in high performance applications, the expensive cost of poly (ether ether ketone) (PEEK, 100,000 $/ton) certainly becomes the bottleneck of wide use. Therefore, great efforts have been devoted to the modification of PEEK by filling, compound and blending.Our lab possesses deeply theoretical basis and richly practical experience in the synthesis, modification and processing of PEEK. The aim of this paper is to add the organic modified montmorillonite (OMMT, 3,662 $/ton) to PEEK matrix so as to reduce the cost of expensive PEEK besides improve the properties such as strength, modulus, thermal stability. Therefore, the combination of OMMT and PEEK may supply the competitive materials with the satisfactory performance-price ratio in high temperature engineering applications to broaden the range of use. In addition, in order to obtain PEEK/OMMT nanocomposites, polyetherimide (PEI) and polyethersulfone (PES) were adopted due to their good solubility and compatibility with PEEK. The PEI/OMMT and PES/OMMT nanocomposites were firstly prepared by solution mixing, and then PEEK/PEI/OMMT and PEEK/PES/OMMT nanocomposites were prepared by melting blending. Two-step method helped to disperse montmorillonite in the PEEK matrix with nano-size, but also effectively enhanced the mechanical properties and thermal properties of PEEK/PEI and PEEK/PES compounds.On the basis of the corresponding literatures, a systematic research on the species of MMT, the optimum condition of OMMT, preparation and properties of PEEK/OMMT binary compounds and PEEK/PEI/OMMT or PEEK/PES/OMMT ternary compounds were performed in this paper. The conclusions are as follows:1. Zhejiang montmorillonite is choosed as a research object, which is due to its high content of montmorillonite, small amount of impurity , low charge density of a half unit cell (< 0.4ξ), easy dispersion with nano scale in polymer matrix. It is most important that its modified effect on montmorillonite is the best. With the regard of the modifiers, the effect of octadecyltrimethyl ammonium chloride is most obvious.2. For Zhejiang montmorillonite, the optimum condition of achieving the largest interlayer spacing (d=4.18 nm) is that the modifier is octadecyltrimethyl ammonium chloride (ODTA), the pH value is 7, reaction time is 1 hour, reaction temperature is 60℃, the amount of modifier is 2.5CEC (cation exchange capacity).3. A series of PEEK/OMMT microcomposites (POMCs) were prepared based on PEEK and different addition amount of OMMT. It should be noted that the used OMMT is that Zhejiang montmorillonite and its interlayer spacing is 4.18 nm. The XRD results of POMCs showed that the interlayer spacing of OMMT decreased to approximate 1.39 nm when OMMT was compounded with PEEK. The decrease of interlayer spacing suggested that the chain of C18 between the silicate layers should be decomposed and the modified Na-MMT (OMMT) almost returned to the former aggregation state (Na-MMT, d=1.21 nm) before the polymer chain came into the silicate layers. Moreover, TEM micrograph indicated that the PEEK did not effectively diffuse into the clay galleries during the swelling period. As a consequence, the silicate layers existed in closely stacked state and the OMMT was dispersed with microscale in the PEEK matrix after the processing, which was in good agreement with XRD results. In addition, the OMMT tended to agglomerate with the OMMT loading.4. The DSC results of POMCs exhibited that the presence of OMMT had marginal influence on the glass transition temperature (Tg) and melting temperature (Tm) of PEEK in the composites. This should result from the coexistence of the baffling effect of inorganic MMT and plasticization of the salt small molecule. The crystallization temperature (Tc) basically decreased except for POMC1 as the OMMT content increased. Namely very small amounts of clay dramatically increased the rate of crystallization. However, high clay concentrations reduced the rate of crystallization. The addition of OMMT has two effects on the crystallization behavior of PEEK. On the one hand, OMMT as nucleation agent promote the crystallization of PEEK; on the other hand, OMMT as inorganic filler increase the melt viscosity of PEEK so as to restrict the regular arrangement of PEEK chains, as the result of hinder the crystallization of PEEK. More obvious the effect of promotion is, the higher of crystallization rate becomes; whereas the stronger the effect of encumbrance is, the lower of crystallization rate becomes. TGA results suggested that small amount of OTAC did not influence the thermal stability of PEEK and temperature at degradation rate of maximum of all POMCs were higher compared to pure PEEK in the temperature range of 550–650 oC. This improvement in the thermal stability can be owed to the high thermal stability of layered silicate in the PEEK matrix. In other words, layered silicate particles in the polymer matrix cumbered transfer of quantity of heat and decreased velocity of decomposition. For example, the temperatures of 5% and 10% weight loss of POMC10 were higher 9 oC and 10 oC than those of pure PEEK respectively.5. The complex viscosity of POMCs was higher than that of pure PEEK, and the complex viscosity of POMCs gradually increased with the increase of OMMT. This should be ascribed that the lamellae of montmorillonite has played a restrict role in polymer chain movement.6. Although we obtained the microcomposite rather than the nanocomposite for PEEK/OMMT system, all POMCs exhibited the improvements in modulus and strength due to the reinforcement effects of the OMMT fillers. Moreover, the reinforcement effects gradually enhanced with the increase of OMMT loading. Namely as the addition of filler to polymer matrix, the dispersed fillers make the crack propagation path longer, absorb a portion of the energy and enhance the plastic deformation. Therefore, the surface fracture energy increases and the modulus and strength the composites should increase with the volume percentage of the filler. The elongation at break of these composites decreased with the increase of OMMT loading. This may be due to the development of cracks around the fillers. It was worth noting that the addition of OMMT could enhance the flexible modulus and tensile modulus values for about 31% and 40% increments respectively, at the OMMT content of 10 wt%, with the slight loss of elongation at break.7. In order to obtain the PEEK/OMMT nanocomposites, PEI and PES were adopted. Firstly, PEI/OMMT and PES/OMMT nanocomposites were prepared by solvent mixing. XRD data showed that some excess quaternary ammonium modifier will be dissolved in chloroform again. As a result, the interlayer spacing of PEI/OMMT or PES/OMMT slightly decreased than that of OMMT. Moreover, the interlayer spacing of PEI/OMMT or PES/OMMT further increased by thermal treatment above 270 oC. The phenomenon explained that polymer chains of PEI or PES had entered into the interlayer of montmorillonite. In addition, TEM micrograph indicated that the montmorillonite dispered in polymer matrix with the intercalated and exfoliated state.8. A series of PEEK/PEI/OMMT or PEEK/PES/OMMT nanocomposites (PPIMs or PPSMs) were prepared based on PEEK and PEI/OMMT or PES/OMMT compounds. XRD and TEM results showed that the state of montmorillonite in PPIM 0.5, PPSM 0.5 and PPSM 1 is exfoliated, whereas the status of montmorillonite in PPIM 1, PPIM 3 is a wide range of intercalation. For PPSM 3, the state of montmorillonite is also intercalated, and the interlayer spacing is almost 1.54nm.9. DSC results exhibited that Tg of PPIM or PPSM compounded with OMMT (PPIMs or PPSMs) was higher than that of the unmodified PPIM or PPSM, whereas Tc, Tm,△Hm and Xc of them were lower than those of the unmodified PPIM or PPSM. TGA results indicated that PPIMs and PPSMs increased thermal stability with the addition of montmorillonite compared to the unmodified PPIM or PPSM. For example, the temperature of 5% and 10% weight loss of PPIM 3 increased by 5 oC and 24 oC than that of the unmodified PPIM respectively, and the temperature of 5% and 10% weight loss of PPSM 1 synchronously increased by 16oC than that of the unmodified PPSM.10. The viscosity of PPIM or PPSM compounded with OMMT (PPIMs or PPSMs) was higher than that of the unmodified PPIM or PPSM, and the viscosity of PPIMs or PPSMs gradually increased with the increase of OMMT. This should be ascribed that the lamellae of montmorillonite has played a restrict role in polymer chain movement.11. The modulus and strength of PPIM or PPSM compounded with OMMT (PPIMs or PPSMs) were higher than those of the unmodified PPIM or PPSM, and the modulus and strengh of PPIMs or PPSMs gradually increased with the increase of OMMT. When the addition amount of OMMT was lower, the range of increase in modulus and strength was obvious. When the addition amount of OMMT was higher, the range of increase in modulus and strength weakened due to the aggregation of OMMT. In addition, the elongation at break gradually decreased with the increase of OMMT.