Search results

This paper aims to gain a greater insight into the molecular level changes occurring in lac‐epoxy blends, at elevated temperatures for different intervals of time. It is also to determine the changes in key physico‐chemical parameters of these blends, before and after applying thermal stress on these blends.

Films of lac‐epoxy blends, applied on tin panels, were baked at 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as these were otherwise difficult to examine through conventional IR techniques, using KBr pellet method. The results obtained were compared and reported. The blends were also tested for different physico‐chemical parameters like scratch hardness, flexibility, adhesion, acid resistance, etc.

On baking the blends of lac‐epoxy resin at 200°C for different time intervals, the strained three membered epoxy ring apparently break open, releasing some free hydroxyl groups, which react with carboxylic groups in lac resin to form ester linkages, resulting in condensation. In terms of different physico‐chemical parameters, blends of 70 per cent lac:30 per cent epoxy were found to be better in performance than blends of 50 per cent lac:50 per cent epoxy and blends of 30 per cent lac:70 per cent epoxy resins, baked at 200°C for different time intervals. Adhesion and acid resistance of lac‐epoxy blends were very good compared with the parent resins.

The spectral studies on lac‐epoxy blends were done qualitatively. Although desirable, quantitative studies could not be carried out, due to the inherent difficulties in handling the resins.

Lac‐epoxy blends may find an important role in printing inks, varnishes and finishing industries owing to their very good adhesion, gloss, scratch hardness and resistance to the action of acids.

As of now, there is no record of specular‐reflectance and derivative spectrometric studies on lac‐synthetic resin blends. This paper represents the first attempt to obtain and correlate reflectance data with physico‐chemical changes. It also highlights the convenience of the method and the scope of sophisticated data analysis, including derivative spectrometry and spectral subtraction techniques.

To find out the molecular level changes in lac‐MF blends, occurring due to the effect of thermal stress on the blends at elevated temperature and at different intervals of baking time.

Films of lac‐MF blends, applied on tin panels were baked at 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as they were otherwise difficult to examine through conventional IR techniques, using KBr pellet method, due to their amorphous and tacky nature. The results obtained were compared and reported.

On baking the blends of lac‐MF resin at 200°C for different time intervals, cross‐polymerisation sets in via esterification and condensation. In addition to this, etherification may take place among different molecules of lac and MF resin. In terms of different physico‐chemical parameters, blends of 7:3 (w/w) lac:MF and of 1:1 (w/w) lac:MF were found to be better than blends of 3:7 (w/w) lac:MF, baked at 200°C for different time intervals.

Chemical researches on lac‐synthetic resin blends have been typically limited due to the complex nature of resins and also due to the lack of suitable modern tools and techniques. This has been solved using state‐of‐the‐art instrumentation and computational techniques, which may prove to be useful to industry and for research.

Lac and its blends retain their significance in diverse fields of applications, ranging from surface coatings and food applications, to the formulation of lacquers, varnishes and in the finishing industry. Findings made in this study could have significant application for such industries from an application point of view.

To date, there is no record of specular – reflectance and derivative spectrometric studies on lac‐synthetic resin blends. This paper represents the first attempt to obtain and correlate reflectance data on such blends. It also highlights the convenience of the method and the scope of sophisticated data analysis, including derivative spectrometry.

To study the changes occurring in lac‐polyvinyl butyral (PVB) resin blends at molecular levels on baking the blends at 200°C for different intervals of time. It was also to ascertain the changes in key physico‐chemical parameters of these blends, before and after applying thermal stress on these blends.

Films of lac‐PVB blends, applied on tin panels were baked at 200°C for different time intervals. The FTIR spectra of the blends were recorded using specular reflectance spectroscopic techniques. The results obtained were compared and reported. The blends were also tested for different physico‐chemical parameters such as scratch hardness, flexibility, adhesion, acid resistance, etc.

On baking the blends of lac‐PVB resin at 200°C for different time intervals; fragmentation reaction, that is breakdown of products into small molecules, takes place in lac‐PVB blends. Side products such as acetic acid emerge on baking the blends. Probably hydrolysis of oxirane ring also takes place leading to the release of free alcoholic groups. The lac‐PVB blends do not show any improvement in scratch hardness and are also not resistant to the action of acids. The blends made by lac‐PVB resin baked at 200°C do not seem to be compatible as no improvement in any of the physico‐chemical parameters was seen.

Mixtures of solvents were tried for dissolving the PVB resin. In most of the solvent mixtures, PVB resin forms big lumps and is not soluble so there is a need for universal solvent for dissolving the PVB resin. The spectral studies on lac‐PVB blends were conducted qualitatively, although desirable, quantitative studies could not be carried out, due to the inherent difficulties in handling the resins.

The parent resins in lac‐PVB blends (baked at 200°C) do not seem to be compatible with one another as there was no improvement in any of the physico‐chemical parameters of the lac‐PVB blends. For making lac‐PVB blends, low range of baking temperature may be tried.

In literature, there is not much evidence of making lac‐PVB blends. This paper is the first one in attempting to obtain and correlate FTIR spectra of the lac‐PVB blends with physico‐chemical changes of the blends. This paper also highlights the convenience of the method and the scope of sophisticated data analysis such as derivative spectrometry.

Applies Fourier transform infrared spectroscopy (FTIR) to the study of lac resin, a complex natural resin of insect origin, and some of its derivatives. Compares the result obtained by this method with those from earlier studies that used classical methods of chemical analysis (the so‐called wet methods). Finds that FTIR has several advantages over the classical methods but, as spectroscopic assignments are still only tentative because of the complex nature of the lac resin, the FTIR data requires supplementing by other instrumental techniques such as FT‐Raman spectroscopy and solid state nuclear magnetic resonance.

To investigate changes at molecular level in lac‐resole blends, occurring due to the effect of thermal stress at higher temperatures and different intervals of baking time.

Films of lac‐resole blends were applied on tin‐panels and baked at 200°C for different time intervals. The baked films were examined by specular reflectance spectroscopy, as they were otherwise difficult to examine through conventional IR techniques, using KBr pellet method. The results obtained were compared and reported.

When lac‐resole blends are baked at 200°C, in addition to possible chromic ring structures, esters linkages are formed between lac and resole molecules through cross linkages among different reactive sites of lac and PF resin. Blend of 70 per cent lac: 30 per cent resole, baked at 200°C for 20 min was found to be the best in terms of different physico‐chemical properties.

Lac‐synthetic resin blends are structurally complex in nature. Chemical researches on such blends have been typically limited due to lack of modern tools. The present method, to determine molecular level changes in lac‐resole blends due to heating effects, using state‐of‐the‐art instrumentation and computational techniques, opens a new field for research and industry.

Lac and its blends retain their significance in the surface coatings and food applications, in the formulation of lacquers, varnishes and in the finishing industry. This study could have significant implication for such industries from application point of view.

As of now, there is no report of specular reflectance data on lac‐synthetic resin blends. This paper represents the first attempt to obtain and correlate reflectance data on such blends. It also highlights the convenience of the method and the scope of sophisticated data analysis, including derivative spectrometry.

The purpose of this paper is to find out a convenient chemical treatment for seedlac and shellac (semi‐refined and refined commercial forms of natural resin lac, respectively) for preventing degradation during storage at room temperature condition.

Seedlac and shellac are treated with a dilute solution of an antioxidant before storage. This method has not been attempted before. The changes in the physico‐chemical properties of both untreated and treated resins are investigated periodically during storage.

Antioxidant delays the degradation of seedlac and shellac at least by six to eight months during the early period of storage. It is further observed that oxalic acid, used in the trade during conversion of seedlac into shellac by hot filtration for imparting gloss on shellac flakes for attracting buyers), causes rapid polymerisation of shellac resulting in zero value (100 percent decrease) of flow (fluidity) within 30 months of storage, whereas, shellac prepared without treatment of oxalic acid could be stored beyond that period without a significant deterioration in its qualities.

Antioxidants are known to be scavengers of OH groups. Lac resin (shellac and seedlac) contains five hydroxyl groups and one carboxyl group. Thus, only one dilute concentration of antioxidant is used to avoid possible modification of seedlac and shellac.

Consumers of shellac are not aware of the ill effect of oxalic acid treatment being practiced by processors. The results obtained in the present study will help consumers to advise processors suitably before purchase and will be able to store shellac for a longer period if it is not treated with oxalic acid. The consumers may also use an antioxidant to delay degradation of seedlac/shellac.

The results obtained in this paper, regarding the effects of treatments of antioxidant and oxalic acid are not available in any previous publication. These are reported for the first time.

The purpose of this study is to enhance the functional properties of Hessian fabric through resin finishing. Hessian bags made of lignocellulosic jute fiber are commonly used to pack, store and transport agro-commodities, including horticultural crops such as rice, potato, onion and wheat. However, because of high water affinity, these bags undergo degradation in properties due to moisture release by the stored commodities themselves. Exposure to natural elements, e.g. rain and dew, also causes moisture absorption in hessian bags. Once the bag gets moistened, degradation of jute bags starts due to microbial attack, leading to loss in tensile strength and change in extensibility, leading to ultimate breakage in warp and weft directions of the fabric.

To overcome the degradation in the functional properties of hessian fabric due to exposure to moisture and microbial attack, the application of semi-synthetic polymeric materials was carried out.

Tenacity, bursting strength, puncture resistance, tear strength and breaking load, as well as life cycle of resin-treated jute fabric was found to be better than control jute.

To the best of the authors’ knowledge, no recent reports of resin finishing on jute (hessian) fabric with semi-synthetic resins are presently available, other than coating with rubber.

The purpose of this study is to improve the coating properties of shellac–epoxidised novolac blends by treatment with melamine formaldehyde resin (MF) at ambient temperature for its use as a coating material.

Epoxidised-novolac resin was synthesised by epoxidation of novolac resin with epichlorohydrin. Novolac resin was synthesised by reaction of phenol with formaldehyde in acidic medium. Shellac was blended with the epoxidised-novolac resin in solution in varying ratios and treated the blends with MF resin in fixed ratio. Coating properties of the treated compositions were studied using a standard procedure. The compositions were characterised with Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and scanning electron microscopic (SEM) spectroscopy.

Treatment of shellac–epoxidised-novolac blends with MF resin improved water and alkali resistance of the blends, besides enhancing gloss. Gloss in all the blends was uniformly increased on treatment with MF resin. Water resistance of the blends tremendously improved after treatment with MF resin. Contact angle of the blends against water increased while decreased against ethylene glycol and dioxane. The compositions were more resistant to polar solvent than non-polar ones, suggesting that the compositions shifted to hydrophobic (lipophilic) nature on treatment with the MF resin.

A specified concentration of MF resin was used in the study. Different concentrations of the MF resin can also be tried for treatment of shellac–epoxidised-novolac blends to see the effect of the resin on the blends.

Treatment of shellac–epoxidised-novolac blend with MF resin improved the coating properties of the blends. The formulation SeNB-64 is the best with high gloss, good impact, scratch hardness and water resistance, and hence can be used as coating material for metal surfaces.

Blending of shellac with epoxidised-novolac resin and treatment of the blends with the MF resin was done for the first time. The formulation SeNB-64 can be used as coating material for metal surfaces.

The purpose of this paper is to improve the properties of shellac by blending with novolac and to study the thermal behaviour of the blends with an ultimate aim to use as surface coating material.

Novolac was synthesized by reaction of phenol with formaldehyde in a molar ratio of 1:0.8, in acidic condition. Blending of shellac with novolac was done in solution and films of the blends, prepared on glass slides and tin panels, were baked at 150°C for 15 minutes. Properties of the films were studied as per standard procedures.

Films of shellac‐novolac blends showed improvement in gloss and impact resistance compared to those of shellac alone. Gloss of blends increased with the increase in concentration of novolac and further increased on baking the films. Scratch hardness of shellac decreased on blending with novolac. Baked films of the blends showed resistance to heat and water. Films of shellac‐novolac blends were found to be more resistant to polar solvents compared to non‐polar solvents.

Shellac, prepared from kusmi seedlac, was used in the study. Besides shellac, dewaxed decolorized lac (DDL), dewaxed lac (DL) and bleached lac (BL) could also be used for study on blending with novolac.

Blending of shellac with novolac improved the film properties of shellac. The study suggests that the compositions can be utilised in developing formulations of coating material with improved properties for metal surfaces.

The formulations based on modification of shellac with novolac and study of the film properties utilising various instruments are novel. The formulations based on shellac and novolac can find applications in the field of surface coating with desired purposes.

The purpose of this paper is to improve the properties of shellac by blending with epoxidised novolac resin for its use as coating material for metal surfaces.

Epoxidised-novolac resin was synthesised by epoxidation of novolac resin, which in turn was synthesised by reaction of phenol with formaldehyde. The epoxidised-novolac resin was blended with different weight ratios of shellac ranging 10-50 weight per cent with an interval of 10 weight per cent. Films of the blends were studied for different coating properties using standard procedure.

Significant improvement in coating properties of shellac such as gloss, scratch hardness and impact resistance was observed on blending with epoxidised novolac resin. Resistance towards water and alkali increased, while acid resistance decreased, with the increase in concentration of epoxidised novolac resin in the blends. Contact angle measurement revealed that blends showed more resistance towards polar solvent than non-polar ones.

Epoxidised-novolac resin used in the study was synthesised of epoxy equivalent of 187. Epoxidised-novolac resin of different epoxy equivalent can also be synthesised and used for blending and studying the properties.

Blending of shellac with epoxidised-novolac resin improved the coating properties of shellac, which was further enhanced with the treatment of butylated melamine formaldehyde resin. The formulation can be used as coating material for metal surfaces.

Blending of shellac with epoxidised-novolac resin was done for the first time. The formulation can be utilised for developing coating material for metal surfaces.