Rajeev Mehta

Bio: Rajeev Mehta is an academic researcher from Thapar University. The author has contributed to research in topics: Epoxy & Ultimate tensile strength. The author has an hindex of 19, co-authored 95 publications receiving 1573 citations. Previous affiliations of Rajeev Mehta include University of Illinois at Chicago.

Synthesis of Poly(Lactic Acid): A Review

Abstract: Poly(lactic acid), a bio‐degradable polymer, has been studied extensively during the past 15 years. This paper presents a review on poly(lactic acid) (PLA) with focus on its stereochemistry, synthesis via ring‐opening polymerization, reaction kinetics and thermodynamics, synthesis of low molecular weight polymer, a continuous process for production of PLA from lactic acid, and blends. The different polymerization mechanisms, which have been proposed in the literature, are also summarized. Various catalyst systems, solvents, and reaction temperature and time give products of an entire range of molecular weights, ranging from a few thousand to over a million. Modeling and simulation of the ring‐opening polymerization of PLA is also discussed.

Salvage treatment for recurrent squamous cell carcinoma of the oral cavity

Abstract: Background Squamous cell carcinoma (SCCA) of the oral cavity recurs with a frequency of 25%–48%, a fact that usually portends a poor prognosis. Recent studies have reported salvage cure rates as high as 67%. Investigators have also claimed that restaging recurrent tumors provides useful prognostic information, although this has not been demonstrated with tumors of the oral cavity. The purposes of this study were: (1) to report the patterns of recurrent SCCA of the oral cavity; (2) to examine the benefit of restaging oral cavity tumors, and (3) to compare different treatment modalities in the management of recurrent SCCA of the oral cavity. Materials and Methods Thirty-eight patients who developed recurrent SCCA of the oral cavity were reviewed. Salvage treatment consisted of surgery, chemotherapy, radiation therapy, or a combination of these modalities. Survival analysis was based on the stage of the primary and recurrent tumors and the type of salvage treatment received. Results The overall recurrence rate was 28%. Local recurrence was most common (58%) followed by locoregional (27%) and regional recurrence (16%). Patients who recurred more than 6 months after completion of their primary treatment had improved survival compared with those who recurred within 6 months of initial treatment. Individuals with stage I-II primary tumors had significantly improved salvage time and total survival time compared with those with stage III-IV primary tumors (p < 0.005 and p < 0.001). Conversely, the stage of the recurrent tumor was not predictive of either improved salvage time or total survival time. Patients who underwent salvage surgery had significantly improved salvage time and total survival time compared with those who received chemotherapy and/or radiation therapy (p < 0.001 and p < 0.002). The overall salvage cure rate was 21%. Neither the stage of the primary or recurrent tumors nor the type of salvage treatment received significantly correlated with an improved cure rate. However, the group of patients who underwent salvage surgery approached a statistically significant improvement in cure rate (p = 0.08). Conclusions Squamous cell carcinoma of the oral cavity is most likely to recur at the primary site. The stage of the primary tumor is significantly correlated with survival even after recurrence, but the stage of the recurrent tumor is not significantly correlated with survival. Patients most likely to benefit from retreatment are those who (1) have primary tumors stage I-II, (2) recur greater than 6 months after their initial treatment, and (3) develop recurrences that are amenable to salvage surgery. © 2000 John Wiley & Sons, Inc. Head Neck 22: 34–41, 2000.

Clay Modification by the Use of Organic Cations

Abstract: To render layered silicates miscible with polymer matrices, one must convert the normally hydrophilic silicate surface to an organophilic one, making the intercalation of polymeric chain between silicate layers possible. This can be done by ion-exchange reactions with cationic surfactants. Sodium montmorillonite (Na-MMT) was modified with several organic cationic surfactants. Organoclays with water soluble surfactants were prepared by the traditional cation exchange reaction. An alternative procedure was used to prepare organoclays with water insoluble salts. The basal spacing and thermal behavior of organoclays were characterized by X-ray diffraction, XRD and Thermogravimetric analysis, TGA respectively.

Pristine and amino functionalized carbon nanotubes reinforced glass fiber epoxy composites

Abstract: Multi-phase composites have been studied by incorporating carbon nanotubes (CNTs) as a secondary reinforcement in an epoxy matrix which was then reinforced with glass fiber mat. Different types of CNTs e.g. amino functionalized carbon nanotubes (ACNT) and pristine carbon nanotubes (PCNT) were homogeneously dispersed in the epoxy matrix and two-ply laminates were fabricated using vacuum-assisted resin infusion molding technique. The issues related to CNT dispersion and interfacial bonding and its affect on the mechanical properties have been studied. An important finding of this study is that PCNT scores over ACNT in composites prepared under certain conditions. This is a very significant finding since PCNT is available at a much lower cost than ACNT.

Microfibrillated cellulose and new nanocomposite materials: a review

Abstract: Due to their abundance, high strength and stiffness, low weight and biodegradability, nano-scale cellulose fiber materials (e.g., microfibrillated cellulose and bacterial cellulose) serve as promising candidates for bio-nanocomposite production. Such new high-value materials are the subject of continuing research and are commercially interesting in terms of new products from the pulp and paper industry and the agricultural sector. Cellulose nanofibers can be extracted from various plant sources and, although the mechanical separation of plant fibers into smaller elementary constituents has typically required high energy input, chemical and/or enzymatic fiber pre-treatments have been developed to overcome this problem. A challenge associated with using nanocellulose in composites is the lack of compatibility with hydrophobic polymers and various chemical modification methods have been explored in order to address this hurdle. This review summarizes progress in nanocellulose preparation with a particular focus on microfibrillated cellulose and also discusses recent developments in bio-nanocomposite fabrication based on nanocellulose.

π-Conjugated Polymers for Organic Electronics and Photovoltaic Cell Applications†

Abstract: The optoelectronic properties of polymeric semiconductor materials can be utilized for the fabrication of organic electronic and photonic devices. When key structural requirements are met, these materials exhibit unique properties such as solution processability, large charge transporting capabilities, and/or broad optical absorption. In this review recent developments in the area of π-conjugated polymeric semiconductors for organic thin-film (or field-effect) transistors (OTFTs or OFETs) and bulk-heterojunction photovoltaic (or solar) cell (BHJ-OPV or OSC) applications are summarized and analyzed.

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Abstract: 4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Poly-Lactic Acid: Production, Applications, Nanocomposites, and Release Studies.

Abstract: Environmental, economic, and safety challenges have provoked packaging scientists and producers to partially substitute petrochemical-based polymers with biodegradable ones. The general purpose of this review is to introduce poly-lactic acid (PLA), a compostable, biodegradable thermoplastic made from renewable sources. PLA properties and modifications via different methods, like using modifiers, blending, copolymerizing, and physical treatments, are mentioned; these are rarely discussed together in other reviews. Industrial processing methods for producing different PLA films, wrappings, laminates, containers (bottles and cups), are presented. The capabilities of PLA for being a strong active packaging material in different areas requiring antimicrobial and antioxidant characteristics are discussed. Consequently, applications of nanomaterials in combination with PLA structures for creating new PLA nanocomposites with greater abilities are also covered. These approaches may modify PLA weaknesses for some food packaging applications. Nanotechnology approaches are being broadened in food science, especially in packaging material science with high performances and low concentrations and prices, so this category of nano-research is estimated to be revolutionary in food packaging science in the near future. The linkage of a 100% bio-originated material and nanomaterials opens new windows for becoming independent, primarily, of petrochemical-based polymers and, secondarily, for answering environmental and health concerns will undoubtedly be growing with time.