Scientific Methods Design of Phenol-Formaldehyde Shell Structures

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Abstract

Carvacrol and Thymol based novel Phenol-Formaldehyde shell structures was designed by in-situ polymerization technique. Diverse operating conditions have been carried out for construction of shell to encapsulate core material i.e. neem oil. Characterizations of prepared microcapsules was carried out by Fourier transform infrared spectroscopy, thermogravimetric analysis, and particle size analyser. The surface morphology of microcapsules was examined by optical microscopy, Leica S8APO stereo microscopy, and scanning electron microscopy. The release rate of core from microcapsules was estimated by UV spectrophotometer, as well as by a simple gravimetric method.

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The results discovered that modified release can be familiar by variable operational procedure for newly invented shell, and constructed shell can be comprehensive to other applications such as drug delivery. Also, the splendour of our present research work is symbolized Thymol-formaldehyde (TF), Carvacrol-Formaldehyde (CF), and Thymol-Carvacrol-Formaldehyde (TCF) as a new shell material for the encapsulation of neem oil and its control release.

Keywords: Carvacrol, thymol, PF microcapsules, neem oil, controlled release.

Introduction

In the regards phenol-formaldehyde (PF) resins are known as one of the oldest commercial synthetic polymers [1], they are used extensively because of their high heat, and excellent electrical and chemical resistance and retention properties [2].

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These resins are used in a wide variety of applications including adhesives [3], surface coating [4], binders [5], moldings [6], and microencapsulation [7].

Microencapsulation is a technique of entrapping liquid, solid or gas molecules within a polymeric shell fabric [8], which is intended to defend contents of core from environment or surrounding to avoid degradation, and the second advantage is that the core is released under controlled conditions [9].

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Also, microencapsulation can be explained as an entrapping of liquid, solid, and gas [10], like unstable or susceptible functional materials within a covering of stable polymeric material [11]. Now this has been commonly applied in various fields like pesticides [12], foods [13], cosmetics [14], pharmaceuticals [15], fragrances [16], textiles [17], self-healing coatings [18,19], perfumery [20], anticorrosive coatings [21,22] etc. All of these microcapsules are encompassed of different polymeric shell materials which involves non-bio-based monomeric components. In continuation very, few are involved in designing of biobased polymeric shells for the same. As PF based shells are robust, easy to prepare, they are used in many applications but attempt to design bio-based PF-resin is very limited [23].

Biobased phenols viz. carvacrol and thymol are naturally occurring and found in essential oils of many plants. They show antimicrobial activity against the growth of a broad spectrum of microorganisms also they shows huge range of pharmacological activities including anti-inflammatory, analgesic, anti-oxidant and anticancer activities have been well-researched, a number of studies have pointed out that plant-derived essential oils may be an efficient substitute to conquer microbial resistance [24-27].

Carvacrol is a monoterpenic phenol biosynthesized from ?-terpinene, through p-cymene and containing methyl and isopropyl functions in the para position to each other on a phenol ring. Carvacrol is the chief natural ingredient in the essential oil fraction of aromatic plants belonging to the family Lamiaceae. Carvacrol has been standard by the Food and Drug Administration for food use and also incorporated in the list of accepted chemical flavorings. Carvacrol has been extensively used in conventional medication, and a huge number of feed additives based on this molecule are at present commercially accessible [28-30].

Thymol is found in thyme essential oil which is the main monoterpene phenol and isomer of carvacrol. Thyme is a labiatae plant which essential oil has demonstrated antiseptic, antispasmodic, anti-inflammatory, immunomodulatory, antioxidant, antibacterial and antifungal properties [31,32]. Up to this, various worker uses essential oil carvacrol and thymol as core material in microencapsulation process using various shells like alginate [10], ca-alginate hydrogel [33], carbohydrate material [34], Arabic gum [35], phosphatidyl choline-based liposomes [36], ?-cyclodextrin [37] etc. Microcapsules possessing diverse shell walls like as phenol formaldehyde [7], urea formaldehyde [38], melamine formaldehyde [39,40], polyurethane [41], and polyurea [42] have been formulated.

It is found that carvacrol and thymol are reported as core material in microencapsulation, but no one reported these as shell materials in microencapsulation technique. Establishment of novel shell is inimitable idea of this work. Phenol-formaldehyde (PF) microcapsules with various cores like neem oil, linseed oil, pendimethalene were produced by applying in situ polymerization technique [7, 43-44].

Neem oil is a phytochemical derived from Indian neem tree, Azadirachta indica. Neem is a large evergreen tree having an outstanding example among plants that has been subject matter of numerous scientific studies concerning its utilization covering a wide range of applications like medicine, cosmetics industry (soap, hair products, body hygiene creams, hand creams) and agriculture (bio-pesticides and Insecticides) against various pathogens, pests, skin diseases, inflammations, and fevers. Though subtle, neem's effects, such as repellency, feeding and oviposition deterrence, growth inhibition, mating disruption, chemo-sterilization, etc. neem oil can control at least 200 species of agricultural. Neem oil results to reduce the risk of exposing the pest's natural enemies to poisoned food or starvation. Neem oil enters the system of insects and blocks the real hormones from working properly and hence impairs their activity which does not kill pests like a neurotoxin but instead affects their behavior and physiology [45-47].

In this work we have made an effort for development of a hazard and waste-free synthesis of shell material and it may be of great use for economical synthesis of bio-based shell material from bio-based phenols. The prettiness of present research work is that the rapid degradation of core material neem oil (bio-pesticide) in the environment was prevented by encapsulation within invented bio-based shell materials thymol-formaldehyde (TF), carvacrol-formaldehyde (CF), and thymol-carvacrol- formaldehyde (TCF). Thus, sustained release of neem oil and improved stability in the environment, which is essential to improve its efficiency.

Experimental

Materials

The materials used in experiments include microcapsule as wall-forming materials thymol (Titan Biotech Ltd., Bhiwadi, Rajsthan, India), carvacrol (Natural Aroma Products Pvt. Ltd. New Delhi, India), formaldehyde (Loba Chemicals, Mumbai, India). The Core material used in the encapsulations is neem oil (Vishal Chem, Mumbai, India). Polyvinyl alcohol (PVA) as a protective colloid, NH4Cl and HCl as pH controllers, while resorcinol as cross-linking agent. Xylene as carrying phase for core were purchased from s d fine chemicals ltd., Mumbai, India.

Preparation of Biobased Thymol-Formaldehyde, Carvacrol-Formaldehyde, and Thymol-Carvacrol-Formaldehyde Novel Microcapsules

The schematic illustration and possible reaction scheme for novel TF, CF and TCF microcapsules fabrication, this section was also taken from the literature with some modifications [18,24,39,45] step by step preparation method is described below.

TF: Microcapsules were prepared by in situ polymerization of (TF) thymol in combination with formaldehyde in an oil in-water emulsion technique as follows. Classically 12 mL of 5% (w/v) aqueous solution of PVA was mixed in of distilled water (68 mL) in a three-neck 250 mL round-bottom flask with stirring arrangement of half-moon teflon blade adjusted to 8mm glass rod with the help of a mechanical stirrer. The flask was placed in a water bath. Under agitation thymol (3.4 g 0.0226 M) and of ammonium chloride (0.5 g 0.009 M) were added in PVA solution. The pH of PVA solution was adjusted to approximately 8-9 using NaOH solution (5% w/v). In another beaker neem oil (10 g) was added slowly to dissolve in xylene (10 mL) by means of a high-speed disperser. An emulsion was allowed to form by adding PVA solution to neem oil solution with high-speed disperser at 5000 rpm for 30 min. After stabilization, aqueous solution of formaldehyde (2.53 g 0.0295 M of 37 wt %) was added. In the starting, reaction was slowly heated to 70 °C temperature under stirring at 450 rpm and maintained at same temperature for the next 2 h. Then HCl (5 % w/v) was also added to maintain the pH at about 3-4 and resorcinol (0.33 g 0.0030 M) was added. Reaction was continued at the same temperature for next 1 h. Microcapsules from the suspension were recovered by filtration under vacuum. These microcapsules were washed well with water and dried under vacuum.
Microcapsules were prepared by in situ polymerization of (CF) carvacrol in combination with formaldehyde in an oil in-water emulsion technique as procedure followed in the scheme 1a only with alteration of carvacrol [3.4 g (0.0226 M)] instead of thymol [3.4 g (0.0226 M)].
Microcapsules were prepared by in situ polymerization of (TCF) thymol [1.7 g (0.0113 M)] and carvacrol [1.7 g (0.0113 M)] in combination with formaldehyde in an oil in-water emulsion technique as procedure followed in the scheme 1a. In this case thymol and carvacrol were used in half mole each instead of using entire 1 mole from only one of them.

Characterization

Microcapsules

Perkin Elmer Spectrum One spectrophotometer was used for recording the FT-IR spectra to identify the linkages and functional groups. Sampling method- Nujol Mull (A Nujol mull is a thick suspension of a solid with the oil. Mulls are made by grinding the solid and oil together in a mortar and pestle).

Thermal degradation study was done on a thermo gravimetric analyzer (Shimadzu TGA 50, Japan) at N2 flow rate of 20mL/min within temperature range of 0 to 700°C, and heating rate of 15°C/min.

Preliminary observations and morphological study of microcapsules were performed on an optical microscope (Labomed Sigma, 2124001, Texas) from 40-100 X resolution. The manifestation (appearance) of microcapsules below optical microscope was snap-shot using digital camera (Canon A 3100), and recorded on Leica S8APO stereo microscope with camera (LAS software. 80X to 160X zoom). Microcapsules were observed for their morphological study under a scanning electron microscope (SEM JEOL JSM 6360 and JEOL JSM 5400, Japan). Particle size was analyzed using a laser particle size analyzer (Mastersizer 2000 Ver. 5.60, MAL100167, Malvern, UK).

Controlled Release Study of Neem oil from Microcapsules

Controlled release of neem oil encapsulated in TF, CF, and TCF microcapsules was studied by weight loss on drying method. As per the procedure described as follows The known amount of dry microcapsules were taken in a Guch Crucibles (Grade No. 4) with 10mL xylene and stirred wobbly for 2 min and then kept for about 1 h at room temperature. The sample was filtered and allowed to dry in the Guch Crucible for 1 h at 40 °C; the dried residue was then weighed to calculate the loss in weight. The same method was repeated at regular time intervals till no loss in weight of microcapsules was observed. Each and every time, microcapsules were treated with fresh xylene of the same amount and neem oil was quantitatively analyzed by a UV spectrophotometer (UV-3600 Spectrophotometer, North America).

Results and Discussion

The objective of the present work is to decorate biobased phenol formaldehyde resins as shell having new properties and applications microencapsulation of neem oil. To achieve this objective many steps have to be performed, the preparation of novel biobased microcapsules from thymol, carvacrol and thymol-carvacrol were completed in our research laboratory by insitu polymerization process and curing by resorcinol.

Scientific Methods Design of Phenol-Formaldehyde Shell Structures. (2019, Dec 20). Retrieved from https://studymoose.com/scientific-methods-design-of-phenol-formaldehyde-shell-structures-essay