Renewable and sustainable biobased materials: An assessment on biofibers, biofilms, biopolymers and biocomposites

With the public’s mature demand in recent times pressurized the textile industry for use of natural colorants, without any harmful effects on environment and aquatic ecosystem, and with more developed functionalities simultaneously. Advanced developments for the natural bio-resources and their sustainable use for multifunctional clothing are gaining pace now. Present review highlights historical overview of natural colorants, classification and predominantly processing of colorants from sources, application on textiles surfaces with the functionalities provided by them. Chemistry of natural colorants on textiles also discussed with relevance to adsorption isotherms and kinetic models for dyeing of textiles.

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Natural Colorants: Historical, Processing and Sustainable Prospects

OBJECTIVE: To evaluate the antibacterial potential of aqueous and acetone extracts of galls of Quercus infectoria by determination of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values. 
MATERIALS AND METHODS: The extracts from the galls of Q. infectoria at 10 mg/ml were screened against three Gram-positive bacteria (Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis and Bacillus subtilis) and three Gram-negative bacteria (Escherichia coli NCTC 12079 serotype O157:H7, Salmonella typhimurium NCTC 74 and Pseudomonas aeruginosa ATCC 27853). The MIC of the extracts were then determined using the twofold serial microdilution technique at a concentration ranging from 5 mg/ml to 0.0024 mg/ml. The MBC values were finally obtained from the MIC microtiter wells which showed no turbidity after 24 hrs of incubation by subculturing method. 
RESULTS: Out of the six bacterial species tested, S. aureus was the most susceptible. On the other hand, the extracts showed weak inhibitory effect against S. epidermidis, B. subtilis, S. typhimurium and P. aeruginosa while there was no inhibition zone observed for E. coli O157. The MIC values of the extracts ranged from 0.0781 mg/ml to 1.25 mg/ml whereas the MBC values ranged from 0.3125 mg/ml to 2.50 mg/ml. The MBC values of aqueous extract against S. aureus and S. typhimurium were higher than their MIC values. The MBC value of acetone extract against S. aureus was also higher than its MIC value. Interestingly, however, the MIC and MBC values of acetone extract against S. typhimurium were the same (1.25 mg/ml). 
CONCLUSION: The aqueous and acetone extracts displayed similarities in their antimicrobial activity on the bacterial species and as such, the galls of Quercus infectoria are potentially good source of antimicrobial agents.

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Research Paper - The potential of aqueous and acetone extracts of galls of Quercus infectoria as antibacterial agents

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

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Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

Background The recent rise in awareness of safe food and changing consumer attitudes have brought many innovations in packaging technology. Consumers are increasingly demanding natural food colorants such as carotenoids, betaines, anthocyanins and chlorophylls rather than synthetic dyes for food applications. As a result, smart packaging based on natural colorants and biopolymers has been introduced as the latest technology in the food packaging field. Smart products not only protect food from environmental hazards, but also send real-time signals (colorimetric, chemical, or electrical) to consumers for changes in the packaging environment and food quality. Scope and approach This paper reviewed the pH-sensitive smart packaging films based on natural food colorants and biopolymers and key applications in the food industry. Technological aspects associated with the natural colorant-based pH-responsive packaging films, biopolymer-based smart packaging, and the importance of natural colorants compared with synthetic dyes are discussed. The most commonly used colorimetric indicators indicating changes in pH, the application of smart food packaging films in real food systems, and the trend of future research were investigated. Key findings and conclusions Based on natural food colorants, smart packaging monitors the qualitative properties of foods in real-time, including freshness, microbial growth, and chemical changes in the product, through visual changes and quantification of pH changes in the food. It provides a fast and reliable inline assessment of food quality and safety. Nevertheless, future studies should consider commercially sustainable key points such as consumer acceptance and trust, cost, regulatory considerations (i.e. labeling) and multifunctional performance of smart films.

pH-sensitive (halochromic) smart packaging films based on natural food colorants for the monitoring of food quality and safety

Introduction of natural dyes into modern dye houses is very promising green chemistry concept which should be popularized more and more to reduce the dependency of wool dyeing on some toxic and non-biodegradable synthetic dyes (Azo and benzidine dyes). In the present study, an attempt has been made to investigate the possibility of wool dyeing with Adhatoda vasica extract as a natural dye. A beautiful color palette of shades of varied hue and tone were obtained by using different mordants. The effect of various metal salts (ferrous sulphate, alum and stannous chloride) and natural tannin extracts (gallnut, pomegranate peel and babool bark) as mordants on color and fastness properties of dyed wool samples was comparatively evaluated. Dyeing experiments were performed with and without mordants, using pre-mordanting technique. The color of dyed woolen yarn was investigated in terms of CIELab (L*, a* and b*) and K/S values; and fastness properties were determined as per ISO and AATCC standard test methods. As confirmed by exhaustion studies, a substantial portion of metal salts remained in residual mordant baths. The results of using biomordants for wool dyeing were comparable with that of the metallic mordants in terms of color strength and fastness characterisctics. Biomordants produced quite different color gamuts as expected from a mordant and thus offer full potential to replace metal salts in wool dyeing.

Ecological dyeing of Woolen yarn with Adhatoda vasica natural dye in the presence of biomordants as an alternative copartner to metal mordants

The current study deals with the use of Terminalia arjuna natural dye as an ecofriendly finishing agent for producing highly functional antimicrobial and fluorescent woolen yarn along with the evaluation of kinetic and thermodynamic adsorption characteristics. The effect of pH on the adsorption was investigated, showing an increase in adsorption capacity with decreasing pH over the range of 2–9, with maximum adsorption at pH 3.5. Two kinetic equations pseudo-first order and pseudo-second order were employed for determining adsorption rates. The pseudo-second order equation provided the best fit to experimental data with an activation energy of 105.58 kJ mol−1, indicating chemisorption. The equilibrium adsorption data was fitted to Langmuir, Freundlich and Redlich–Peterson adsorption isotherms. The adsorption behavior accorded with the Redlich–Peterson isotherm with exceptionally high regression coefficients for dyeing temperatures of 50, 70 and 90 °C with dye concentration varying from 0.5–10% (o.w.f). Comparative results of the colorimetric properties (CIEL*a*b* and K/S) using a spectrophotometer under D65 illuminant (10° standard observer) and color fastness (light, wash, and rub) of dyed woolen yarns were studied to quantify the effect of metal mordants. The antimicrobial potential of Terminalia arjuna solution and dyed woolen yarn were assessed in terms of percentage inhibition of bacterial growth against a wide variety of bacterial strains, showing more than 85% inhibition. Reduction in antimicrobial activity of dyed woolen yarn was observed with mordanted samples, however they were found to retain more antimicrobial activity as compared to unmordanted samples as a function of successive washing cycles. The chemical nature of different mordants and wool–mordant–dye complex forming ability were found to have significant impact on the colorimetric and fluorescence characteristics of dyed woolen yarn.

Antimicrobial and fluorescence finishing of woolen yarn with Terminalia arjuna natural dye as an ecofriendly substitute to synthetic antibacterial agents

An eco-friendly dyeing of woolen yarn by Terminalia chebula extract with evaluations of kinetic and adsorption characteristics.

In the present study, Terminalia chebula (Myrobalan/Harda) natural dye extract was used for the development of eco-friendly shades on woolen yarn with different hues and tones. The effect of dye concentration on color strength (K/S) of woolen yarn dyed with T. chebula was assessed. Increasing the concentration of dye decreased lightness (L*) values of woolen yarn samples, indicating darker shades. Different metal salts such as alum, ferrous sulfate, and stannous chloride were used to enhance the fastness properties (light, wash, dry and wet rubs) of dyed woolen yarn. Pre-treatment of woolen yarn samples with metal salts has shown encouraging results with better fastness properties and enhanced color strength values. Five percent ferrous sulfate mordanted samples show greater saturation with increasing dye concentration from 0.5 to 15 % (o.w.f.). Fourier-transform infrared (FT-IR) analysis of T. chebula dye extract shows presence of carbonyl and hydroxyl functionalities.

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Mohd Shabbir

Papers

Natural Colorants: Historical, Processing and Sustainable Prospects

Ecological dyeing of Woolen yarn with Adhatoda vasica natural dye in the presence of biomordants as an alternative copartner to metal mordants

Antimicrobial and fluorescence finishing of woolen yarn with Terminalia arjuna natural dye as an ecofriendly substitute to synthetic antibacterial agents

An eco-friendly dyeing of woolen yarn by Terminalia chebula extract with evaluations of kinetic and adsorption characteristics.

Application of Terminalia chebula natural dye on wool fiber—evaluation of color and fastness properties