Benzoxazine (Bz) monomer was synthesized from renewable cardanol, a by-product from cashew-nut industry, using a solventless approach. The monomer was encapsulated in poly(styrene) (PS) shells by solvent evaporation technique to obtain spherical microcapsules. The microcapsule dimensions and core content could be tailored by optimizing the operating parameters, particularly stirring speed and PS concentration. Successful demonstration of this simple and versatile methodology widens the scope for large-scale application of benzoxazines in the field of self-healing. © 2014 Elsevier Ltd. All rights reserved.

Bimlesh Lochab

Chemistry

(SoNS) School of Natural Sciences

Sharma P.

Shukla S.

Kumar D.

Kumar Roy P.

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Shiv Nadar University

Materials Letters

Polybenzoxazines are evolving as a new class of phenolic resins with a tremendous amount of applications. The ease of structural designing, synthetic procedure, and polymerization reactions are attractive to affect their properties ensuing as an effective substitute for many existing polymers. The nonrenewable origin, toxicity, and increasing cost of petro-based raw materials are alarming issues. Therefore, the emergence of sustainable benzoxazines, especially based on naturally abundant, agro-waste origin cardanol is encouraging as it allows both solventless synthesis of monomers and processing to form highly thermally stable thermoset resins. The inherent functionalities in cardanol benzoxazine provide a platform for further structural modifications to advance their applications as adhesives, composites, and energy storage devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Macromolecular Chemistry and Physics

Cardanol Benzoxazines: A Versatile Monomer with Advancing Applications

This chapter explores the utility of cardanol as a potential feedstock for the synthesis of benzoxazine monomers and polymers. Cardanol is a renewable phenolic compound obtained from the plant Anacardium occidentale L. Commercially it is produced as cashew nut shell liquid (CNSL) as a byproduct of cashew nut processing. It is currently under exploration as a valuable phenolic reagent in benzoxazine monomers and polymers. Cardanol-based benzoxazines are attractive monomers due to their sustainable aspect, opportunities for solventless synthesis, and processing. To date, Cardanol monomers have primarily been utilized for adhesive and composite applications, but they are ideal candidates for a variety of other applications, which need further exploration. © 2017 Elsevier Inc. All rights reserved.

Advanced and Emerging Polybenzoxazine Science and Technology

Cardanol-Based Benzoxazines and Their Applications

Benzoxazine resins, although exhibiting attractive properties; particularly high thermal stability and near zero- shrinkage, suffer from a major drawback associated with its high curing temperature. In view of the Lewis acidity associated with the Zn4O nodes in a zinc based metal organic framework [Zn4O(BDC)3, MOF5], we considered it of interest to explore its potential as a curing accelerator for a representative biobased benzoxazine resin. MOF 5 was solvothermally synthesized and characterized using different techniques including powder X-ray diffraction (PXRD), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and Nitrogen physisorption measurements. Bio-based benzoxazine resin was synthesized by mannich type condensation of cardanol and aniline with formaldehyde under solventless conditions, the structure of which was confirmed using FT-IR and 1H-NMR. The curing behavior of the synthesized resin was systematically investigated using non-isothermal Differential Scanning Calorimetry (DSC). Introduction of MOF 5 led to a shift in the curing profile to lower temperature, the extent of which was proportional to the amount of MOF 5 in the formulation. DSC studies were performed at different heating rates to establish the kinetic parameters associated with the curing of the resin. Activation energy, as calculated using Kissinger Akahira Sunose method, was found to concomitantly decrease from 98 kJ/mol to 58 kJ/mol upon addition of MOF 5 (5 \% w/w). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ChemistrySelect

Metal-Organic Frameworks as curing accelerators for benzoxazines

This paper deals with the preparation of sustainable benzoxazines that exhibit enormous potential to compete with the existing petro-based advance performance thermosets. The phenolic component used for the synthesis of benzoxazine is derived from naturally occurring cardanol, which is obtained from cashew nut tree, Anacardium occidentale. Polyethylene terephthalate (PET) was chosen as a sustainable feedstock for the amine fraction used to prepare the benzoxazine monomer containing amide linkages. Microwave-assisted aminolysis of PET was performed to obtain bis(amino-ethyl) terephthalamide (BAET) and α,ω-aminoligo(ethylene terephthalamide) (AOET), which were employed as the difunctional amine for the preparation of bis-benzoxazines. In comparison to the traditional method, microwave-assisted aminolysis of PET was found to be significantly faster, and the reaction completion time could be brought down appreciably. Mannich-like condensation of cardanol with PET-derived terephthalamides and paraformaldehyde led to the formation of bis-benzoxazines with amide linkages, the structure of which was confirmed through FT-IR and 1H NMR spectroscopy. The curing behavior of the bis-benzoxazines was studied using nonisothermal differential scanning calorimetry. The presence of amide linkages in addition to the polar group formed during the ring opening of benzoxazines led to the improvement in adhesive strength, which was quantified in terms of lap shear strength. © 2015 American Chemical Society.

ACS Sustainable Chemistry and Engineering

Sustainable Bis-benzoxazines from Cardanol and PET-Derived Terephthalamides

A series of benzoxazine monomers with varied benzoxazine functionality from 1 to 3 (mono, bis, and tris) is prepared by reacting agrowaste-derived cardanol with higher functionality amines. The ring opening polymerization study of cardanol-based benzoxazine monomers is investigated by three modes, namely, solution (nuclear magnetic resonance and gel permeation chromatography), bulk (differential scanning calorimetry), and theoretical (B3LYP and 6–31+G**) calculations to analyze the role of number of benzoxazine functionality in curing behavior of the monomers. It is found that the presence of higher and close vicinity of benzoxazine functionality in the monomer promotes faster ring opening, rapid polymerization conversion, and enhancement in the average molecular weight buildup. The activation energy for the curing process is found to decrease from 144–113 kJ mol−1 from mono- to tris-benzo­xazine monomer. Thermodynamically, the presence of higher benzoxazine moiety reveals the curing process is highly exergonic as supported by theoretical calculations. Free energy for successive protonation varies from −9.54 to −24.68 eV for mono- to tris-functionalized monomer. The effect of number of functionality in monomer on its curing behavior – a complete study is reported to offer sustainable monomers/polymers for futuristic materials applications. (Figure presented.) . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Kinetics behind a Strategy for Modulation of Sustainable Benzoxazines: Experimental Study and Its Theoretical Verification

Exploration of sustainable alternatives to chemicals derived from petro-based industries is the current challenge for maintaining the balance between the needs of a changing world while preserving nature. The major source for sustainable chemicals is either the natural existing plant sources or waste generated from agro-based industries. The utility of such resources will supplement new processed materials with different sets of properties and environmental friendliness due to their biodegradability and low toxicity during preparation, usage and disposal. Amongst other polymers used on a day-to-day basis, phenolic resins account for vast usage. Replacement of petro-based monomers such as phenol and its derivatives either partly or completely utilized for the synthesis of such resins is ongoing. Extraction of natural phenolic components from cashew nut shell liquid, lignin, tannin, palm oil, coconut shell tar or from agricultural and industrial waste, and their utilization as synthons for the preparation of bio-based polymers and properties obtained are reviewed in this paper. This review article is designed to acknowledge efforts of researchers towards the "3C" motto-not only trying to create but also adapting the principles to conserve and care for a sustainable environment. This review paper describes how extraction, separation and recovery of desired phenolic compounds have occurred recently; how substituted phenol compounds, unmodified and modified, act as monomers for polymerization; and how the presence of sustainable phenolic material affects the properties of polymers. There are about 600 references cited and still there is a lot to uncover in this research area. This journal is © the Partner Organisations 2014.

Fulltext

RSC Advances

Naturally occurring phenolic sources: Monomers and polymers

Journal of Polymer Research

Polysiloxane-based core-shell microspheres for toughening of epoxy resins

Macromolecules

Polybenzoxazine Precursors As Self-Healing Agents for Polysulfones

Journal of Thermal Analysis and Calorimetry

Blends of benzoxazine monomers

Journal of Polymer Science Part A: Polymer Chemistry

Methylol-functional benzoxazines as precursors for high-performance thermoset polymers: Unique simultaneous addition and condensation polymerization behavior