Processing Structure Property Relationships in (TPE-E) Nanocomposites - Lab Report Example

?4. Results and discussion The present work describes Fluormica (Somasif ME 100) Prestine clay modified with alkyl-ammoniums and a polymer (PolyesterTPE). The goal was to prepare TPE-E nanocomposites by preparing modified organoclays and melt blending them with different grades of TPE-E (Block copolyester thermo platic elastomers)using extruder (PolyLab ThermoHaake). There is a significant amount of polymers that the produced modified organoclays can be blended with. Modified organoclays are known to be highly dispersible in both polar and non-polar polymers. However, we will use only Polyester TPE of three different grades (Grade: Hytrel 3078, Hytrel 4069 and Hytrel 5556). This area of research is extremely promising because such systems possess higher dispersion then conventional organolclays do. Also, it is worth mentioning that examples from both literature and experimentaly achieved data point out that alkyl-ammoniums used as organo-modifiers have limited applications for apolar polymers. Scheme 1: Alkyl-ammoniums used as organo-modifiers For such polymers interactions with clay is usually low and further entropic barriers prevent mixing of an inorganic clay with the desired polymer. In other words, alkyl chain-clay interactions are low. To overcome this organo-modifiers are used but, as our studies suggest, low thermostability (Changes in composition start to occur at approx. 2200C) of the produced modified clay will limit the scope of potential applications. 4.1 Modification of Clay As it was previously stated, it was necessary to modify Fluormica (Somasif ME 100) Prestine clay to increase its mixability with the polyester TPE. The employed type of clay is hydrophilic. This factor contributes to poor solubility in hydrophobic polymers. It terms of structure, Fluormica (Somasif ME 100) is made of layers which are held together by electrostatic forces. These layers carry the negative charge, while positively charged cations are shared equally between stacks of layers. This structure is not easy to brake, what is another factor to poor mixability. In order to modify the studied clay ion exchange reactions were used. The chemical formulation is Na0.66Mg2.68(Si3.98Al0.02)O10.02F1.96 [65] and the particle size is about 650 nm. (Cation Exchange Capacity is 100 mequiv/mol). Thus it can be presumed that cations such as Na+ and Mg2+ can be substituted by an alkyl-ammonium (Scheme 1) cations. Alkyl-ammoniums carry different hydrophobic groups consequently, producing various hydrophobicity. Hydrophobic chain makes the modified clay more compatible with the organic matrix. Employing different alkyl-ammoniums it will be possible to make the clay compatible with almost any required polymer. Moreover, treatment with described organic modifiers will separate clay plates. This will afford intercalated and exfoliated materials which can be used to produce nanoparticles. To describe the produced modified clay it is necessary to analyse Fourier transform infrared spectrosctrum(FT-IR) then move on to X-ray photoelectron spectroscopy (XPS) before finally commenting on thermogravimetric analysis (TGA) curves. 4.2 FT-IR The major peak for all the studied samples occurs at 902 cm-1 (Scheme 2). This wavelength can be associated only with carbon-oxygen-carbon symmetric stretch absorbtion. There is only one peak in this region there are no peaks formed by asymmetric carbon-oxygen-carbon absorbtion. The next major peak occurs at 2925 cm-1 but not for all studied entries. ME 100 and ME100 CC do not possess such peak. The formed peak is due to asymmetric stretch of CH2-O group. The described peaks prove the presence of specific bonds in the molecule. Scheme 2: FT-IR spectrums of the modified clay samples. 4.3 XPS On the Schemes 3 and 4 ME 100 is the unmodified clay and all the entries from 2 to 8 present various modifications. It is seen that not all Na+ and Mg2+ are substituted by N+R4. In ME 75 Etho substitution is the most efficient and ME 100 CC shows only slight reduction on Na+ and Mg2+ quantity. No Sample Code O (%) C (%) F (%) Na (%) Mg (%) Si (%) N (%) 1 ME 100 46.83 13.48 10.09 0.54 10.97 17.70 0.39 2 ME 100 Etho 32.41 42.62 6.15 0.13 6.87 11.07 0.76 3 ME 75 Etho 33.33 40.07 6.01 0.13 7.16 11.17 2.12 4 ME 100 ODTMA 30.83 43.96 5.30 0.17 7.23 11.74 0.78 5 ME 75 ODTMA 29.16 53.70 4.17 0.10 4.80 7.27 0.79 6 ME 100 DMDO 26.30 50.57 5.47 0.19 6.70 9.81 0.96 7 ME 75 DMDO 28.29 46.07 6.18 0.33 7.05 10.97 1.10 8 ME 100 CC 43.63 21.04 8.51 0.55 9.88 15.71 0.69 Scheme 3: Atomic compositions on clay layers and surfactant organization in the interlayer galleries of clays. he percentage of carbon also increases. By introducing nitrogen carbon will be introduced through alkyl chains. Organo clays C-C C-N/C-O BE (eV) % BE (eV) % ME100 284.654 82.52 285.757 17.48 100 Etho 284.195 76.6 285.783 23.40 75/25 Etho/CC 284.251 70.99 285.588 29.01 100 ODTMA 284.370 97.99 286.752 13.01 75/25 ODTMA/CC 284.969 63.67 286.803 33.65 100 DMDO 285.000 90.90 286.548 9.07 75/25 DMDO/CC 285.006 90.94 286.625 9.062 100 CC 284.448 53.58 286.238 46.92 Scheme 4: Percentage of carbon atoms bound to carbon (C-C) and nitrogen and oxygen (C-N/C-O) atoms in ME 100 series The same logic can be applied describing scheme 4. Exposing ME 100 to alkyl-ammonium salts will increase the number of carbon-nitrogen/carbon-oxygen bonds but, as it was deduced from scheme 3, substitution is not complete. High number of carbon-carbon interactions for 100 DMDO and 75/25 DMDO/CC is expected because of high carbon quantity in dimethyldioctadecyl ammonium. 4.4 TGA Commenting on the dependence of mass from temperature a slight reduction of mass is observed for all the samples at 900C. This is due to the presence of water. Next till 2200C there are no changes in mass. Starting from 2200C it is necessary to comment on several observations. First, there are absolutely no changes in mass for unmodified ME 100. This fact makes the mentioned compound the most thermo stable, however it cannot be mixed with Polyester TPE. Second, ME 100 CC is the most stable among the modified clay samples. It starts to lose weight at 3000C in contrast to 2200C for all other entries. And finally, changes in composition of alkyl-ammonium salts, generally, will not contribute thermostability of the modified clay. Scheme 5: TGA diagrams of the modified clay samples. 5. Future work and outlook Mainly, there are three methods that help to overcome thermodynamic factors and to obtain the desired nanoparticles. This is either solvent blending, melt blending or in situ polymerisation,. This work in future will be concentrated on employing melt blending of achieved modified organoclays with different grades of TPE-E. The procedure is not new and is described in literature. Melt blending were used by Matayabas et al. In his preparations of PET nanoparticles with different quantities of Claytone –APA. 1200C were used to dry the mixture following extrusion at 2800C. As their work suggest, the increase in the amount of clay will decrease the viscosity of the achieved PET/organomodified clay nanocomposites. This fact point out to the degradation of the polymer used. Degradation was different depending on the structure of the polymer, however, it is affected by low thermostability of the modified organoclay. Another example of melt blending was described by Davis et al. They dispersed two types of organoclays in PET, performing the operation at 2850C. It was possible to produce nanocomposites employing MMT (montmorillonite) exposed to N,N-dimethyl-N,N-dioctadecylammonium. MMT is known to decompose at 2500C. The second sample was 1,2-dimethyl-3-N-hexadecyl imidazolium subjected to hexadecyl-MMT. For hexadecyl-MMT the decomposition temperature is higher, 3500C. In both cases twin-screw extruder was used and it was noted that if the speed is low (20 rad/sec) then dispersion is much better than operating at higher speed (30 rad/sec). Also, it was noted that degree of exfoliation depends on the residence time spent in the extruder. Taking into account all the published literature, there is not much information describing dependence between structure of produced nanocomposites and their obtaining conditions. It was noted that surfactant’s decomposition can be lowered if the process is conducted at approx. 2600C but not at usual 2800C. MMT is not the only substrate that can be used in the described processes. Cloisite 10-A is an interesting example leading to thermally stable nanocomposites. By altering the structure of Cloisite 10-A it was possible to afford products more thermally stable then in case of montmorillonite. Taking into account the listed examples from literature, it can be stated that preparation of modified organoclays to melt blend with different grades of TPE-E (Block copolyester thermo platic elastomers) using extruder (PolyLab ThermoHaake) is a method that has far going potential practical applications. Reference list Sontikaew, S., 2008. PET/Organoclay Nanocomposites, A Thesis submitted for the degree of Doctor of Philosophy, Brunel University: London Read More