G. Ajeesh

Influence of chemically and plasma-functionalized carbon nanotubes on high-performance polymeric nanocomposites

This investigation highlights different surface functionalization processes of multi-walled carbon nanotubes (MWCNTs) and their effects on mechanical properties of polyetherimide nanocomposite. Surfaces of MWCNTs were modified by chemical process and by low-pressure plasma process. There is a significant change in physicochemical characteristics of MWCNTs after chemical and low plasma treatment evident from scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy studies. Due to surface modification of CNTs, there is a significant change in surface morphology and increase in oxygen functionalities such as C=O, C–O, and COOH especially evident in low-pressure plasma treatment; however, differential scanning calorimeter and thermogravimetric analysis studies reveal that thermal properties of the composite do not alter as such. There is a significant increase in mechanical properties of high-performance polymeric nanocomposites when surface-functionalized MWCNTs are dispersed in polymeric matrix; however, surface characteristics of the composite remain almost unchanged evident from contact angle and surface energy studies.

Influence of surface activated carbon nano fiber on thermo-mechanical properties of high performance polymeric nano composites

This investigation highlights the influence of plasma modified carbon nano fiber (CNF) on the various properties of poly ether ketone (PEK). CNFs were modified with oxygen plasma under low pressure to enhance the interfacial adhesion between the reinforcement and matrix. Significant changes are evident in the elemental composition of oxygen and carbon on the plasma modified CNFs as observed by X-ray photo electron spectroscopy. Based on results from compression and tensile strength, significant change in the mechanical properties of the composites is observed. Dynamic mechanical thermal analysis (DMTA) reveals that the storage modulus increases on reinforcing modified CNF in PEK. The increase in modulus is noticeable only up to 1.5% wt reinforcement of CNF, while higher percentage of reinforcement leads to decline in properties. DMTA studies also clearly shows that the dispersion of CNF is not uniform after 1.5% of CNF reinforcement. However, differential scanning calorimeter and thermo gravimetric analysis studies reveal that the thermal properties of the CNF reinforced composite do not vary significantly. Thermal conductivity results show a substantial increase in the thermal conductivity of polymeric composites on increasing the reinforcements. Transmission electron microscopy (TEM) analysis reveals that there is uniform dispersion of CNF in PEK. TEM also clearly shows that higher percentage of CNF leads to agglomeration. Physico-chemical analysis indicates that the contact angle increases on increasing the reinforcements. These findings would be highly useful to make way for PEK composites for high temperature and high strength application.

Effect of Atmospheric Pressure Plasma Modification on Polyimide and Adhesive Joining with Titanium

This investigation highlights the effect of surface modification on polyimide by atmospheric pressure plasma treatment with different exposure time. Surface modification of polymer by plasma treatment essentially creates physical and chemical changes such as cross-linking and formation of free radicals. It also forms oxygen functionalization in the form of polar groups on polymer surface, hence improving the wetting and adhesion properties. It is observed that surface energy of the polymer increases with increasing exposure time of atmospheric pressure plasma. However, prolonged exposure time of plasma results in deterioration of the surface layer of polyimide resulting in degradation and embrittlement. Scanning electron microscopy and atomic force microscopy analysis reveal that there is a considerable morphological change on the polymer surface due to atmospheric pressure plasma treatment. X-ray photo electron spectroscopy analysis reveals that the oxygen functionalities of polymer surface increases significantly when polyimide is exposed to atmospheric pressure plasma. Untreated and atmospheric pressure plasma-treated polyimide sheet are adhesive bonded by employing polyimide adhesive as well as with titanium substrate. Due to surface modification of polyimide, it is observed that there is a significant increase in lap shear tensile strength, and therefore, this technology is highly acceptable for aviation and space applications.

High-performance fire-resistant polymeric nanocomposite for aerospace applications:

This investigation essentially highlights development of novel high-performance fire-resistant polymeric nanocomposite with respect to its orientation towards future generation aviation. Therefore, an attempt has been made to increase thermal stability and fire resistivity of phenolic/cotton fabric reinforced polymer composite, which is desirable for aircraft interiors. There is considerable increase in adhesion characteristics of phenolic fabric reinforced polymer composite due to atmospheric pressure plasma treatment. The phenolic fabric reinforced polymer is subsequently coated with nanosized calcium silicate reinforced polybenzimidazole composite in order to increase thermal stability and fire resistance property. Thermogravimetric analysis reveals that polybenzimidazole-coated fabric reinforced polymer shows significantly better thermal stability than the uncoated phenolic fabric reinforced polymer. There is a significant increase in the limiting oxygen index characteristics of polybenzimidazole-coated fabric reinforced polymer when compared to the uncoated phenolic composite resulting in considerable improvement in fire resistivity of the polymers.

Effects of high energy radiation and thermo-chemical environments on polyetherimide composites: futuristic approach to nuclear waste storage

This research highlights the effect of radiation, chemical and thermal environments on mechanical and thermal properties of polyetherimide (PEI) composites. The tests are conducted on specimens made from PEI and PEI reinforced with modified Carbon Nano Fibre (CNF). The specimens are subjected to gamma radiation doses of 5 MGy, which is equivalent to the cumulative dose of radiation from spent nuclear fuel until the end of complete radioactivity. The exposed samples are further subjected to highly corrosive and thermal environments. Studies under transmission electron microscopy reveal that there is a uniform dispersion of modified CNF in PEI. Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) indicate that there are no significant changes in thermal properties of PEI and PEI composite when exposed to aggressive environments. It is observed that there is a marginal loss in the tensile strength of polymeric samples when exposed to gamma radiation and thermal environments. PEI samples when subjected to alkaline corrosive environments show significant loss in the tensile strength. There is a significant decrease in the molecular weight of PEI under alkaline corrosive environments as seen from Gel Permeable Chromatography (GPC).

Feasibility of polyetherketone (PEK) composites: a solution for long-term nuclear waste storage

This investigation highlights the effect of radiation, chemical and thermal environments on mechanical and thermal properties of polyetherketone (PEK) composites and its rationale for long-term nuclear waste storage. The tests are conducted on samples manufactured using PEK and PEK reinforced with modified carbon nano fibre (CNF). The specimens are subjected to gamma radiation doses of 5 MGy, which is equivalent to the cumulative dosage of radiation from spent nuclear fuel until the radioactivity neutralises completely. Studies under transmission electron microscopy (TEM) reveal that there is a uniform dispersion of modified CNF in PEK. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicate that there are no significant changes in thermal properties of PEK and PEK composite when exposed to aggressive environments. It is observed that tensile strength of polymeric samples remains unchanged when exposed to gamma radiation and thermo-chemical environment.