Rakesh Kumar Khandal

Sulfur containing optical plastics and its ophthalmic lenses applications

Abstract Plastics produced from the sulfur-based monomer are excellent materials with many optical applications such as ophthalmic lenses, fiber optics and non- linear optics. High refractive index plastic materials are able to reduce the curvature, edge and center thickness of lenses. Sulfur containing plastics such as sulfide, polysulfide, and sulfur containing vinyl compound, thioacrylate, polythiol and isocyanate/isothiocyanate based monomers have demonstrated high refractive index, high Abbe number, good impact strength, excellent machinability, good tintability and good transmittance. In the present article, various sulfur containing plastics with different types of monomers for ophthalmic lens applications are reviewed.

Novel way of making high refractive index plastics; metal containing polymers for optical applications

Abstract Plastics are being preferred in almost all possible applications of materials. Several new applications including optical devices are being developed using plastics replacing conventional materials like inorganic glass etc. For the optical applications, the most important properties of plastics essential for their desired performance include refractive index, Abbe number, optical clarity, etc. The biggest challenge in developing suitable materials for optical applications has always been to meet the criteria of high refractive index along with a high Abbe number. Normally, if the refractive index increases, the Abbe number automatically decreases. The researchers have tried several approaches to deal with this typical challenge without which it is not possible to develop novel optical plastics. Presently the most popularly known optical plastics includes polymers such as polymethacrylates, polyurethanes, polycarbonates, polystyrene and diethylene glycol bis allyl carbonate. The latest material of high refractive index plastics with a refractive index of 1.67 belongs to the polythiourethanes chemistry. Several approaches are being tried world over, to develop materials of high refractive index. One of the approaches being pursued for enhancement of refractive index of existing monomers pertain to the incorporation of metals or metal salts in the matrices. The other commonly tried but difficult to achieve approaches pertain to the preparation of nanoparticles or nanocomposites.

Development of High Refractive Index Plastics

Abstract Optical plastics have been the priority area of research for material scientists worldwide, mainly, to find alternative materials to glass, a conceptual optical material in use over the years. There are numerous advantages of using plastics for optical applications, in particular for ophthalmic applications over glass. Recently, the researchers have been putting their efforts to develop novel plastic materials to meet requirements of ophthalmic industries. The present review compiles the recent developments in the area of optical plastics. The aim is to present the current state-of-the-art in the field, besides analyzing the various aspects of developing optical plastics. The review presents various possible approaches to achieve the desired properties e.g. high refractive index of the optical plastic materials.

Certain Rheological Aspects of Functionalized Guar Gum

Guar gum and its derivatives are highly important industrial hydrocolloids as they find applications in various industrial sectors. Guar is a polymer of high molecular weight and its aqueous solutions exhibit unique rheological properties, which has led to its wide acceptance by the industry. In certain industrial applications low molecular weight guar and its derivatives are needed, and conventionally chemical depolymerisation of guar is carried out for this purpose. Radiation processing is a novel and green technology for carrying out depolymerization and can be an ideal substitute for chemical depolymerisation technique. In order to study the effect of radiation on guar derivatives, three types of derivatives have been taken in the present study: carboxymethyl, hydroxyethyl, and methyl guar. The effect of 1–50 KGy radiation dose on the rheological behavior of these derivatives has been studied, and the results have been described in the present paper. The effect on storage and loss modulus with respect to frequency and effect on viscosity with respect to shear rate have been discussed in detail.

Novel Nanocomposite Optical Plastics: Dispersion of Titanium in Polyacrylates

Polyacrylates have become the preferred materials for optical applications replacing the conventionally used glass due to their superior optical clarity. The major disadvantage with polyacrylates is their low (1.40–1.50) refractive index besides their poor impact resistance. The improvements in refractive index as well as mechanical properties can be achieved by way of incorporation of metals or metal compounds in the matrix. A novel methodology for the incorporation of high refractive index metals into low refractive index polymeric materials to improve the refractive index and impact resistance of the latter has been developed. With the in-situ formation of nanoparticles of , the refractive index of polyacrylates improved from 1.45 to 1.53 and the Abbe number increased from 40 to 57. One of the interesting dimension of this study pertains to the possibility of tailor-making of the two key optical properties of materials by way of varying the amount of being formed in-situ. Thermal stability and impact resistance of nano dispersed (4.3% by wt. of Ti) polyacrylates are found to be better than the neat polyacrylates. Moreover, -containing polyacrylate is of light weight. TEM, SEM, and IR analysis confirms the in-situ formation of nanoparticles of . Gamma irradiation has been used as an eco-friendly technique for polymerization. The developed compositions can be cast polymerized into clear and bubble free material for optical applications.

Studies on Development of Polymeric Materials Using Gamma Irradiation for Contact and Intraocular Lenses

For the development of materials for contact lenses and intraocular lenses, the selection criteria is based on the (i) capacity to absorb and retain water, (ii) hydrophilicity and hydrophobicity, (iii) refractive index and (iv) hardness besides the other essential properties. Various monomers are being studied to develop suitable materials for such applications. Selection of suitable monomers that can be converted into optical materials of desired characteristics is the most essential step. In the present paper, an attempt has been made to develop suitable optical polymers based on 2-hydroxy ethyl methacrylate (HEMA), N-vinyl pyrrolidone (NVP), methyl methacrylate (MMA), methacrylic acid (MAA), and styrene. Compositions were prepared in such a way that polymers of varying hydrophilicity or hydrophobicity could be obtained keeping HEMA as the base (main) monomer. For polymerization, gamma irradiation (Co-60 as a source) was used. The results of the study showed that: (i) an increase in NVP and MAA content brought in an increase in hydrophilicity of polymerized HEMA (pHEMA), while the addition of styrene and MMA decreased hydrophilicity of polymerized HEMA (pHEMA), (ii) polymers for contact lenses with water retention capacity as high as >50 wt.% and as low as <10 wt% with varying content of suitable comonomers can be designed, (iii) polymeric materials for contact lenses can be made by using radiation processing such as Co-60 and (iv) a dose of 40 kGy was found to be ideal for purpose.

Water Quality Issues Needing Technological Interventions: Sustainable Availability for All

The fact that existence of life is entirely because of the availability of water and since water cannot be manufactured, it becomes utmost essential to take care of the various resources of water for sustainability. In order to ensure quality water, the management of water resources requires extreme care and caution. Water is the key resource for life support systems. It is only due to the existence of water that agriculture, aquaculture, animal husbandry, marines, etc. is possible. Due to its unique properties, water is an important raw material for various industrial and household products. As per the recent trends, industrial products based on organic solvents are being reformulated using water. For setting up of any industry, one always ensures the sustainable availability of quality water. Water has also been used for transportation. Whichever purposes the water is used for, it is important that water should be of desired quality; use of poor quality water can be worse than the non-availability of water. Water is not only non-degradable but also it can neither be created nor be destroyed. The unique nature of imbibing everything, water gets in contact with, is the concern! The moment water gets in contact with any surface or a substance, it picks up the various constituents from the matrix in contact, resulting in the conversion of quality water into wastewater. The deterioration of quality starts when the measures for protection of water from contamination are inadequate. Therefore, to avoid spoilage of quality water and to recover quality water from wastewater are the key priority tasks for which technological interventions are needed. The present paper deals with various aspects of availability of quality water.

Challenges in preparation of metal-containing nanocomposites; dispersion of titanium into plastics

Abstract Metal containing polymers are of great interest as they have proven to be the most promising materials for applications such as microelectronics, holography and magnetic recording of information. Metal containing polymers also provide an alternative to even the specialty glass materials conventionally used for optical applications. Metals such as barium, lead and lanthanum have been used to improve the optical properties such as refractive index and mechanical properties such as hardness of optical plastics. The metal-containing optical plastic materials with improved refractive index of as much as 1.60 along with the Abbe number of more than 30 have been successfully designed using these metals by the authors of this paper. To further increase the refractive index without any drop in Abbe number and to improve the hardness of the polymer matrix, titanium would be the most promising metal. Incorporation of titanium in plastic matrices to form homogeneous and optically clear compositions is a challenging task. This paper reviews the state-ofthe- art by which titanium can be dispersed in polymer matrices to form metal containing composites as optical plastics.

Modification of Low Refractive Index Polycarbonate for High Refractive Index Applications

Polycarbonates and polythiourethanes are the most popular materials in use today, for optical applications. Polycarbonates are of two types which fall in the category of low refractive index and medium refractive index. The present paper describes the conversion of low refractive index polycarbonates into high refractive index material by the use of a high refractive index monomer, polythiol, as an additive. Novel polycarbonates, where the properties of refractive index and Abbe number can be tailor made, have been obtained. Thermal studies and refractive index determination indicate the formation of a new polymer with improved properties and suitable for optical applications.

Improvements in Essential Electrical and Physical Properties of Phenol Formaldehyde Resin by Incorporation of Modified Coal Tar Pitch

Abstract Phenol-formaldehyde (PF) resin is used here for making thermosetting composites along with environmentally friendly coal tar pitch(CTP). These PF-CTP composites are made with dual objectives of using environment-friendly CTP to improve the electrical and physical properties of PF resin and to reduce cost of PF resin for final applications. The composites are prepared by a two-step method using standard compression molding technique. Comparing the properties of the samples containing varying amount of CTP with pure PF resin as the reference sample, significant improvements in electrical properties like surface resistivity, volume resistivity and dielectric strength are observed with the increase in amount of CTP. The waterproofing tendency also improved as the amount of CTP is increased. The best properties are observed for the thermosetting composition with 40 phr of CTP.