Rajeev Mehta

Synthesis of Poly(Lactic Acid): A Review

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.

Modeling Impact of Solar Radiation on Site Selection for Solar PV Power Plants In India

Solar power is gaining importance in the light of discussion about climate change and renewable energy sources. In most parts of India, clear sunny weather is experienced 250–300 days in a year. The annual global radiation varies from 1600 to 2200 kWh/m2, which is comparable with radiation received in the tropical and subtropical regions. This paper runs simulation scenarios for various sites in India for technical and financial viability of solar power generation with photo voltaic (PV) technology. Solar radiation data are accessed from National Aeronautics and Space Administration (NASA) website, and other meteorological parameters are collected from Indian Meteorological Department (IMD). The data are fed into RETScreen model to run various simulation scenarios. Feasibility of sites in India to build a 5-MW PV-grid connected power plant from techno-economical and environmental points of view are discussed. A model is run for 31 major sites in India to measure the viability of Solar PV plants at these sites. Financial incentives announced in national solar mission of India have been used as an input to the model. Viability indicators like internal rate of return (IRR), net present value (NPV), cost of electricity (CoE), benefit–cost (B–C) ratio are identified on the basis of the model. A comparison of results is done and the best sites in India are reported.

Preparation and Characterization of Polylactic Acid-Based Biodegradable Blends Processed Under Microwave Radiation

Properties of the biodegradable polymers like PDLLA and PCL can be modified by blending them with each other and with other polymers like Starch. In the present study we have prepared blends of PDLLA, PCL and starch in different proportions and then subjected to microwave radiation. Using microwave, time of reaction has been reduced to 3–30 min as microwave radiation is associated with more even distribution of heat. The results indicate a direct linkage between the polymers indicating the formation of a chemical linkage between the two molecules as opposed to just a physical blend.

Mathematical Modeling of the Poly(lactic acid) Ring–Opening Polymerization Kinetics

The modeling of ring-opening polymerization of (D,L)-lactide to poly(lactic acid) (PLA) has been performed. Except some reported data on the apparent rate constant, there is lack of data in the literature on the rate constants for initiation, propagation and termination steps of PLA polymerization. Using a simple numerical technique, the individual rate constants are evaluated theoretically and the results are compared with the available experimental data for ring-opening polymerization of PLA. The proposed method works well without requiring a polymer chain length independent rate constant. It is also shown that presence of even small amount of impurity (e.g., water) in the reaction kettle can greatly limit the polymer molecular weight.

Mathematical Modeling of the Poly(lactic acid) Ring-Opening Polymerization using Stannous Octoate as a Catalyst

A novel and simple mathematical model to get the polymerization rate constants for the ring-opening polymerization of poly(lactic acid) is described. The model permits evaluation of the degree of polymerization versus monomer-to-initiator ratio curves. The predicted results are compared with the reported experimental data. The value of rate constants for initiation, propagation, and different modes of termination, are also obtained.

Processing of Functionalized and Pristine Carbon Nanotube Epoxy Composites with Silane-Treated Glass Fiber

In this work, an attempt has been made to study the bonding between the silane coupling agents and the glass fiber (GF) surface. The mechanical properties of the composites so obtained have been specifically analyzed. It has been experimentally found that epoxy silane (ES)-treated GF mat in a neat epoxy matrix showed considerable improvement compared to amino silane (AS)-treated GF. The effect of heat treatment on GF has also been looked into. Moreover, a new processing technique has been explored, which involves the use of amino functionalized nanotube (ACNT) and pristine nanotube (PCNT), homogeneously and uniformly dispersed in an epoxy matrix. Additionally, the effect of ES- and AS-treated GF in the presence of PCNTs and ACNTs has been studied and it has been found that AS shows strong interfacial adhesion in the ACNT matrix, whereas ES shows improved mechanical behavior in the PCNT matrix. The findings from this study have certainly helped us design improved fiber reinforced nanocomposites with enhanced mechanical properties suitable for marine structures.

Effect of surface treatment of nanoclay on the mechanical properties of epoxy/glass fiber/clay nanocomposites

Abstract A new method of silane treatment of nanoclays is reported where in the clay is nanodispersed in hydrolyzed silanes. The surface functionalization of Cloisite® 15A nanoclay has been carried out using two different silane coupling agents: 3-aminopropyltriethoxy silane and 3-glycidyloxypropyltrimethoxy silane using varied amounts of silane coupling agents, e.g. 10, 50, 200, and 400 wt% of clay. The surface modification of Cloisite® 15A has been confirmed by Fourier transform infrared spectroscopy. The modified clays were then dispersed in epoxy resin, and glass fiber-reinforced epoxy clay laminates were manufactured using vacuum bagging technique. The fiber-reinforced epoxy clay nanocomposites containing silane modified clays have been characterized using small angle X-ray scattering, transmission electron spectroscopy and differential scanning calorimetry. The results indicate that the silane treatment of nanoclay aided the exfoliation of nanoclay and also led to an increase in mechanical properties. The optimized amount of silane coupling agents was 200 wt%. The nanocomposites containing clay modified in 200 wt% of silanes exhibited an exfoliated morphology, improved tensile strength, flexural modulus, and flexural strength. The improved interfacial bonding between silane modified nanoclays and epoxy matrix was also evident from significant increase in elongation at break.

Microwave Assisted Synthesis of Poly(lactic acid) and its Characterization using Size Exclusion Chromatography

Poly(lactic acid) (PLA) has been synthesized catalytically under vacuum by microwave (MW) irradiation using stannous octoate (SnOct2) as catalyst. The polymerization is carried out at 180○C up to 30 min. PLA with a molar mass of 104 g.mol−1 and a yield over 97% was produced in 20 min by the ring-opening polymerization of L-lactide using (SnOct2) as catalyst under microwave irradiation with a power level of 180 W. The structural investigations are done by NMR and FTIR. The average molar mass of PLA is determined by means of size exclusion chromatography, (SEC). The characterization is done using three different columns. The polymerization rate is much faster with microwave heating than conventional heating. Microwave irradiation gives rapid energy transfer and high-energy efficiency, hence, a faster reaction rate.

Synthesis of Polylactide: Effect of Dispersion of the Initiator

The ring opening polymerization of L-lactide was studied in bulk using stannous octoate as initiator. In some experiments, triphenylphosphine, a Lewis base was also used as co-initiator. The polymerization was carried out at 130°C up to 29 h. The monomer was used after recrystallizing three times with dry toluene. Experiments were carried out using a wide range of monomer to initiator ratio. The averages and distributions of molar masses of resulting PLA have been determined by means of size exclusion chromatography, SEC. It is shown that the (mode, process) procedure of dispersion of the catalyst in polymerization system affects the molar mass distribution of the product as is evidenced by the bimodality or even trimodality observed in the SEC chromatograms.

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Abstract Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (Tg) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.