Indian Journal of Fibre & Textile Research Yo 1.3 I , March 2006, pp. 72-82

Microencapsulation of essential oils and phase change materials

for applications in textile products

Bojana Boha Department of Chemical Education and Informatics, Faculty of Natural Sciences and Engineering, University of Ljubljana,

Yegova 4, 1001 Ljubljana, Slovenia

and

Emil Knez Aero Chemical, Graphic and Paper Industries, Ipavceva 32, 3000 Celje, Slovenia

The paper reports the development and testing of three types of microcapsules for applications i n textile products, namely microencapsulation of antimicrobial essential oils of sage, lavender and rosemary for nonwoven textile shoe insoles; smell-based animal repellents for agricultural textiles, designed to protect plants against damage caused by deer and rabbits; and paraffinic phase change materials (PCMs) for active thermal control garments. III situ polymerisation of melamine­formaldehyde prepolymers was used as the microencapsulation technology in all three cases, based on partly methylated tri­methylolmelamine and hexamethoxymethylolmelamine resin as wall materials and a styrene-maleic acid anhydride copoly­mer as a modifying agent. The microencapsulation process was modified to achieve the desired characteristics of microcap­sule wal ls (different permeabi l i ty and sensitivity/resistance to pressure). Bibl iometric trends in microencapsulation technol­ogy with special reference to textile industries have also been discussed with an overview of main application fields and uses of microencapsulated additives in textile products.

Keywords: Microencapsulation, Nonwoven, Phase change material

IPC Code: I nt. C I .8 C09K5/00, DO I F I I I O

1 Introduction

1.1 Microencapsulation Trends

Microencapsulation includes several technologies for coating micrometer sized particles of finely ground solids, drops of liquids, or gaseous components with protective spherical membranes - microcapsule walls . Microencapsulation can be considered as a typical ex­ample of a knowledge-intensive and dynamic research field with an increasing growth of publications (Fig. I ) . 1 Trends in patent vs. non-patent l i terature i l­lustrate the growth of basic research (non-patent lit­erature), and a faster growth of industrial research rep­resented in waves of patented inventions.

Microencapsulation technologies offer many op­portunities to improve the properties of textiles or to give them new functions. B ibliometric analyses show that the vast majority of publications on microencap­sulation for textile applications are the patents (Fig. 2), i l lustrating the importance of industrial property rights in this specialized field. The first wave of microcap­"ule inventions for textiles broke out in 1 970s and in-

., all the correspondence should be addressed . . � .boh @ntf.uni-Ij .s i .

troduced microencapsulated dyes, pigments, softeners, antistatic agents and fire retardants for textiles, while the second wave of i nventions in the 1 990s brought thermochromic and photochromic materials , antimi­crobials, insect repellents, cosmetic and medical tex­tiles. The third wave, biggest of all, took rise after the year 2000 and covered primarily the microencapsu­lated phase change materials (PCMs).

2500 (ij Q) >- 2000 Q; 0.. C/) C Q) E :::J <..> 0 -0 0 Q; .0 E :::J Z

1970 1975

D "

1980 1985 Year

1990 1995 2000

Fig. I -Yearly growth in new publ ications on microencapsulation in the Chemical Abstracts Plus database

BOH & KNEZ: M ICROENCAPSULATION OF ESSENTIAL OILS & PHASE C HANGE MATERIALS 73

1.2 Microencapsulation Processes

I The selection of microencapsulation processes de­pends on the desired characteristics and uses of textile final products. The properties of microcapsules, their sizes, shapes, wall materials, active substance release mechanisms, method of application, and compatibil i ty with formulation additives have to be adapted to the requirements of textile processing methods and uses of final products . The preparation of microcapsules for textile finishing compositions was in i tially based on coacervation processes and later on polymerisation methods, such as interfacial polymerisation and in situ polymerisation of aminoaldehyde resins.

The coacervation phenomenon takes place in col­loid systems, where coacervate droplets (a macromo­lecular colloid rich phase) surround dispersed micro­capsule cores and form a viscous microcapsule wall ,

701

� w�---------------- -------------------n.

j 501' 0 Non-paten!

C • Patent (1) 40 -- ----------------------I-H-E :::J U ' _____________________ � .g JOT '0 20-;--------Iii .0 � IO -----� �----���HH�� ..... Z

1965 1 970 1 975 1980 1985 1990 1995 2000 Year Fig, 2-Bibl iometric analysis of microencapsulation applications in textiles as per the Chemical Abstracts Plus database

which is then hardened with a cross-linking agent (Fig. 3a) . In polymerisation methods, monomers polymerise around emulsified or dispersed cores and form a solid polymeric wal l . In the i nterfacial polymerisation (Fig. 3b), one of the monomers is typically dissolved in the aqueous phase and the other in a hydrophobic solvent phase, while in the in situ polymerisation (Fig. 3c), monomers or precondensates are added only to the aqueous phase of the emulsion.

1.3 Microcapsule Formulations for Textile Applications

Patents describe different ways of incorporating mi­crocapsules onto or into texti les, such as by spraying, by coating with an air knife or rod coater, by impreg­nation or immersion during the stage of chemical treatment, or by incorporation into plastic carriers, such as polymer foams, coatings and multi layer com­posites, fol lowed by insertion into selected parts of textile clothing. In rare cases, microcapsules are incor­porated directly into textile fibres during the spinning process.

I n a typical example, a suspension of microcapsules has to be formulated for applications on woven or nonwoven texti les. Formulation additives usually con­sist of binders, organic or inorganic pigments and fi l l ­ers, antifoaming agents, and viscosity controll ing agents.

B inders play a crucial role in microcapsule coating formulations. They may be selected from the groups of water soluble polymers (e.g. starch and modified starches, carboxymethyl cellulose, polyvinyl alcohol, and xanthanes), synthetic latexes (e.g. styrene-

Fig. 3-(a) Microcapsules produced by complex coacervation of gelatin and carboxymethyl cel l ulose (transmission stereomicroscopy, x 1 00); (b) dispersion of cross-l inked protein microcapsules, prepared by interfacial polymerisation in water- in-oi l emulsion [transmission microscopy (x 1 00), photographic enlargement (x lO) ] ; and (c) coating of microcapsules, produced by ill situ polymerisation of mela­mine-formaldehyde resins (SEM, x 1 900)

74 INDIAN J. FIBRE TEXT. RES., MARCH 2006

butadiene, polyvinyl acetate or acrylate latexes with anionic andlor nonionic emulsifiers), aminoaldehyde resins (e.g. urea- and melamine-formaldehyde resins, dimethylol ethylene urea, dimethylol dihydroxy ethyl­ene urea, and dimethylol propylene urea), and sil icones.

1 .4 Applications of Microcapsules in Textile Products

The idea of using microencapsulation technology in textile products was born soon after the first introduc­tion of the industrial production of microcapsules for carbonless pressure-sensitive copying papers in the middle of the previous century. Possibil ities of using microencapsulation technologies in textile products are numerous, and have already been described in detai I .2

The main application fields and uses of microencap­sulated additives i n textile products are summarised in Fig. 4 . The products include: dyes and pigments l - 1 4 ; i ngredients for transfer pri nting 1 5-20 ; thermochromic . I 2 1 -26 h h ' . I "7-35 I matena s ; p otoc romIc matena s· . ; cata ysts and enzymes36. 37; fire retardants38-47; sizing and bond-. 48 49 bl ' d d' Ing agents . ; OWIng an expan Ing agents; water-proofing agents50-53 ; detergent components, such as enzymes54-62; bleaching and whitening additives63-74;

8edroSl:aUc pOoling

Solvent dyeing

Dot dyeing and sped<1ed printing H Dyes ard pignents � SCreen printing

Trar'lsfer printing

Uquid c:rystals

� ThermoclYomic materials Thennochromic dyes

Re�rsib� photochromic dyes Pholochromic materials � VVrinkJe reoo�ry agents

� Surface modifying agents Catalysts ard Enzymes

antifoami ng agents 75-77 ; dry c1eani ng agents 78; soften-d . . 79-84 f d f ers an antistatIc agents ; ragrances an per urnes 85-95 . I I 96- 1 02 d d d d' . i' ; Insect repe ents ; eo orants an ISInleC-

tants 1 03- 1 1 0; active i ngredients for cosmetic textiles 1 1 1 - 1 1 5 ; adsorbents and decontaminants 1 1 6- 1 1 8 ; thermal regulation agents based on sunlight conver­sion"9 ; and heat storage materials based on phase h . I 1 20- 1 13 C ange matena s . -

This paper describes microencapsulation of antimi­crobial essential oils for shoe insoles, animal repellents for agricultural texti les, and PCMs for active thermal control garments. In situ polymerisation of melamine­formaldehyde resins was used as the microencapsula­tion technology in all three cases.

The idea of fragranced textiles containing microen­capsulated essential oils and aromas is more than thirty years old. Aromatic capsules have been developed, which either slowly release their contents through semipermeable walls or have impermeable walls which burst open by mechanical pressure and rubbi ng when the wearer moves. A new generation of aromatic textiles entered the market when better washfast bind-

Enzymes

Bleaches

r1 Detergents � Mtifoarring agents

Perfumes

Dyes '-i Dry deaning chemcalS

H Essenl�1 oils I Fragrarces ard perfumes I Aromas and perfumes

Mosquito repellents

H Insect. repellents Tk:k repellents

18 ���ij Molhproofflg agents

Fire retardingfe:dingushing agents Fire reta-dants � -{

Anlibaderial plant oils and I Deodorants & disinfectants Sizing agents

� Antifungal plant oilS and extracts I

Adhesives and activato� Sizirg and bonding � AntimaobiaJ agenlS Cross.-Wnk.ing agents

Antioxidants

Light-weight leather substitutes MOISturizilg agents

waterproofing coatings H � l.{ � Cosmetic textiles Sub-cutaneous fat controllers

BICMling ;n:! expandirg AntisWp materials I- Anti-cellulite agents

8Ipandable sewing threads Diuretics

Bkxxj circulation stimulants 8cpansion agents

� Wate(-proofmg agents WfiA..- proofirg

I H Water purification absorbent

Fillers ard deconta'l'linants Military decontamination agents I

Textile softeners in detergents

� Antiststtc; agents Laundry � J -1

Sunlight conversion agents Thermal agents

Fragrances in texliJe soneners Phase change materials I Fig. 4-Appl ications of microcapsules in texti le products

BOH & KNEZ: MICROENCAPSULATION OF ESSENTIAL OILS & PHASE CHANGE MATERIALS 75

ers were introduced. According to patent l i terature, these fragranced textile products retain the aroma over several years, keep the microcapsules over 25 washing cycles or resist dry cleaning. Typical products include fragranced garments, bed l inen, and textiles for furni­ture and car interiors.

In addition to the pleasant aroma, several essential oils also possess antimicrobial , fungicidal and deodor­ant properties. Based on some essential oils, antibacte­rial printing compositions for garments and antimicro­bial nonwoven textile shoe insoles with prolonged ac­tivity, based on pressure-sensitive microcapsules which release the active ingredient during walking, have also been developed.

Textiles with prolonged insect repellent effects have been developed to protect the wearer against mosqui­toes and ticks, or to protect textiles by applying micro­encapsulated mothproofing agents. Appl ications in­clude insect repelling carpets and curtains, panty hoses with durable insect repel lence, sprays for mothproof­ing treatment, and animal repellent textiles for agri­cultural and horticultural uses: Similarly as in the case of microencapsulated fragrances, many improvements in microencapsulated repel lents on textile supports deal with binders for improved wash fastness.

The fastest growing microencapsulation application in textiles has become sportswear and special technical apparel, based on micr.oencapsulate'd PCMs with heat and cold absorbing capacity . Several firms compete for the intellectual property rights and market shares in this field. Sportswear shops are offering coats, j ackets, boots, socks and gloves with the active thermal control technology.

PCMs are a sub-group of heat storage materials with a dynamic heat exchange process taking place at the melting point temperature. When a PCM undergoes a phase change transition from solid to liquid, energy is stored in the form of latent heat at a constant tempera­ture. Accumulated latent thermal energy is then re­leased when the PCM solidifies again. In general, the higher the PCM's latent heat of phase change is, the more thermal energy a material can store. The transi-' , , tion process is complet�ly reversible. To overcome' practical problems of'.. solid-liguid phase , transitions, , PCMs are microencapsulated and turned into solid formulations or suspensions for applications in various thermal management applications. In textile applica­tions, microcapsules with PCMs are incorporated into fabrics with enhanced thermal properties, functioning as heat absorbers or as barriers against cold. In heating ,

PCMs, the temperature gradient flows from the PCM into the body, and the phase transition temperature is above the body's normal skin temperature. The cooling PCMs have a phase transition temperature below the body's normal skin temperature. When chilled below their transition temperature, the temperature gradient flows from the body into the PCM.

For garments that could better keep a constant tem­perature, microencapsulated PCMs were first incorpo­rated in the fibres. The idea was further developed by several researchers, but it was difficult to incorporate enough PCM in the fibre structure to get a thermal re­sult while retaining the fibre' s mechanical characteris­tics. To overcome this problem, PCM microcapsules were , incorporated into textile products in different ways, such as coated on fibres and fabrics with a binder or built into polymer foam inserts and compos­ites with two or more layers. Several texti le applica­tions were then developed, such as improved diving suits, fire wear, special working clothes, military uni­forms, gloves and shoes, leather products and special textile products containing electric heating circuits.

2 Materi}lIs and Methods .

2.1 Materials l' Partly methylated trimetnylolrl1elamine and a hex­

amethoxymethylolmelamine resin (both procured from Melamin;< Slovenia) were used as ;prepolymers for mi­crocapsule wal�s. Styrene�maleic ' acid anhydride co­polymer with' average mol. weight 350,000 (Hercules) was used as a modifying agent and emulsifier for ill situ polymerisation. Analytical grade sodium hydrox­ide (Kemika, Croatia) and sodium metabisulphite Na2S20S (BASF) were used for the termination of po­lymerisation reaction and removal of free formalde­hyde from the suspension of microcapsules.

Essential oils of lavender (Lavandula hybrida), rosemary (Rosmarinus officinalis) and sage (Salvia officinalis) in mixtures with isopropylmyristate as a solvent were used as antimicrobial active agents. Con-

, centrations of 1 0%, 25% and 40% essential oil in the solvent were microencapsulated.

Daphne ' (Dragoco, Austr-ia) was used as an animal repellent, based on a mixtu� essential oils and other volatile co�pounds. Its main c'�mponents are vanillin, heliotropin (3 ,4-methylenedioxybenzaldehyde), cy­clamaldehyde . 3-( 4-isopropy l-phenyl)-2-methy lpropa­nal] , methionyl acetaldehyde, citronellol (3 ,7-dimethyl-6-octen- l -ol) and dimethylphthalate as a solvent. Four paraffinic hydrocarbons (AGS, Turkey and Rubitherm,

76 INDIAN 1. FIBRE TEXT. RES., MARCH 2006

Germany) with melting points 25°C, 28°C, 40°C and 50°C were used as PCMs for microencapsulation.

Polyester, polypropylene and cellulose-polypropy­lene nonwoven textiles (30, 40, 45 and 250 g/m2) were used as textile carriers for the shoe i nsoles with anti­microbial activity. Polypropylene nonwoven textiles (20 and 30 g/m2) , and cellulose-polypropylene non­woven textile (40g/m2) were used as carriers for Daphne animal repel lent microcapsules. The impreg­nated agricultural textiles were dried and cut into strips (length 3 m, width 5 cm).

Acrylic latex, styrene-butadiene latex, and water­soluble binders (polyvinyl alcohol and carboxymethyl cellu lose) were added to microcapsule suspensions prior to textile impregnation.

2.2 Methods

A d'f' d " I . . h d b 1 34 135 mo I Ie In sltu po ymensatlOn met 0 y . was used as the basic microencapsulation process for the preparation of microcapsules with melamine­formaldehyde prepolymers as a wall material, and a

- -

Water + aminoaldehyde resin + anionic polyelectrolyte

modifying agent

Emulsification of a Jipophylic core material

(active substance) -

styrene-maleic acid anhydride copolymer as a modi­fying agent. The latter served both as an emulsifier and as a polycondensation i nitiator, which enabled the po­Iymerisation to develop only at the surface of the emulsified oil droplets (future microcapsule cores), and not throughout the whole water phase (Fig. 5) .

The melting points of PCMs were determined by differential scanning calorimetry (Perkin Elmer Pyris- l ) . The microcapsule size and size distribution were measured by Coulter Counter TA I l apparatus and by Alkatel Ci lias Laser Granulometer 7 1 5 . Aque­ous suspensions of microencapsulated PCMs were dried by a B lichi B290 spray dryer. Scanning electron microscopy was performed by JEOL JSM-6060LV microscope at accelerating voltage 1 5 kV w;th micro­capsule coating C + Au/Pd.

For the impregnation of nonwoven textiles with mi­crocapsule formulations, a technique for the transport

. of the textile carrier through the impregnation basin was used (Fig. 6). Headspace gas chromatography was

Polycondensation (change of

temperature and pH)

Microcapsule hardening, removal of

residual monomers

Fig. 5-Microencapsulation by in situ polymerisatioll of amino-aldehyde resins l34

Plain non- Suspension of woven microcapsules in a texti le binder solution

Drying . oven

Curing oven

Non-woven textile irnpregnated with

microencapsulated scents

Fig. 6--- A process for preparing nonwoven textile carriers saturated with microencapsulated active agents l3S

BOH & KNEZ: MICROENCAPSULATION OF ESSENTIAL OILS & PHASE CHANGE MATERIALS 77

used for the determination of quantities of essential oil in new and worn textile shoe insoles. Textile insole samples containing microencapsulated essential oils were put i nto measuring flasks and exposed to ele­vated temperature at 1 60"C for 45 min. Gaseous phases were then analysed by gas chromatography using internal standards (flame-ionisation detector, capillary column HP Ultra 1 and HP Carbowax M20, ini tial temperature 60°C, temperature gradient 2SClmin, and final temperature 1 90"C).

Mechanical testing of shoe insoles was performed by walking (experimental person 80 kg) on average 3 km per day for a total distance of 50 km.

The antimicrobial activity of shoe insoles made of nonwoven textiles impregnated with microencapsu­lated antimicrobial essential oils was tested by a stan­dard method for the determination of antibiotic activ­i ty. Clinical isolates of Trichophyton mentag rophytes, Candida albicalls, and Staphylococcus aureus were used as reference microorganisms. The tests were per­formed with 1 0% and 40% concentrations of essential oils in isopropylmiristate, and with the further dilu­tions to 1 :2 , 1 :4, 1 :8 , 1 : 1 6, 1 :32, 1 :64, 1 : 1 28, 1 :256, 1 :5 1 2 and 1 : 1 024.

Field testing of microencapsulated animal repellents on textile strips was carried out in the winter season on two agricultural fields near the forest. The pressure of wild animals on agricultural surfaces was strong in snow because the availabi l ity of natural food was very limited. The efficacy of the repellent agricultural tex­tiles was studied on deer and rabbits. Textile carriers (3 m long and 5 cm wide) impregnated with microen­capsulated repellen t Daphne were tested using baits with 10 one-year-old apple branches in each bait ( l m long branches, 10 cm distance between branches, I SO m distance between baits); the methodology as de­scribed earlierl 36 was used. The number of damaged branches per bait ( 1 - 1 0) was used as the criterion to evaluate damage caused by animals .

3 Results and Discussion

3.1 Microencapsulated Antimicrobial Essential Oils for Textile Shoe Insoles

Impermeable pressure-sensitive microcapsules contain ing antimicrobial mixtures of sage, lavender and rosemary essential oils were successfully pro­duced by the process described earlierl 34. 1 35 and then applied onto nonwoven textiles by immersion impreg­nation. Shoe i nsoles were produced from dried im­pregnated textiles. An example of essential oil compo-

nents present in non-ruptured microcapsules in a new polypropylene shoe insole, detected by the headspace gas chromatography, is given in Table I .

Chromatographic analyses, performed prior to and after the mechanical testing of shoe insoles, proved that the antimicrobial essential oils were kept in the microcapsule core until its wall was broken by a me­chanical pressure during walking. Tests confirmed that the microencapsulation of volatile essential oil s en­abled a sustained and prolonged release of essential oils from microcapsules during wearing of shoes. The results of headspace gas chromatograpy showed that after 50 km of walking, shoe insoles still contained 62-72% of microencapsulated active ingredients. The re­lease was more intense on insole parts exposed to higher mechanical pressure.

In in vitro antimicrobial activity tests against Staphylococcus aureus, a non-encapsulated mixture of 40% essential oil and 60% isopropyl miristate (sol­vent) was proven to have bactericidal activity. Bacte-

Table I -Composition analysis of new shoe insoles made of a nonwoven polypropylene texti le impregnated with microencap­sulated essential oil (Lavalldlila hybrida. Rosmarinus officilla/is

and Salvia (�fficillalis) mixture in isopropylmyristate using gas chromatography

Essential oil com- Conc. of Weight of AmountJpair of ponent in micro- component, % nonwoven shoe insoles capsule g I m" (450 cm

2)

mg

a-pinene 1 . l0 1 .54 69.30

Camphene 0.85 1 . 1 9 53.55

Sabinene 0.02 0.03 1 .26

p-pinene 0.37 0.52 23.3 1

1 ,8-cineol 3.60 5.04 226.80

Limonene 0.8 1 1 . 1 3 5 1 .03

a-thujone 0.93 1 .30 58.59

p-thujone 0.24 0.34 1 5 . 1 2

Campherol 1 . 1 8 1 .65 74.34

Borneol 1 .36 1 .90 85.68

Linalool 5.00 7.00 3 15 .00

Terpi nene-4-o1 0.94 1 .32 59.22

Linalyl acetate 0.74 1 .04 46.62

Cariophylene 0.25 0.35 1 5 .75

Isopropyl my- 74.00 1 03 .60 4662.00 ristate (solvent)

Other components 8.6 1 1 2.05 542.43

Total 1 00.00 1 40.00 6300.00

78 INDIAN J . FIBRE TEXT. RES., MARCH 2006

riostatic activities of above 40:60 mixtures were also observed using di lutions from I : 1 to 1 : 1 024 (0.42 mg/ml). For mixtures of 1 0% essential oil and 90% of isopropyl miristate, the bacteriostatic activity was evi­dent in dilutions up to 1 : 1 28 .

In vitro tests against Candida albicans showed a fungicide activi ty of 40:60 mixtures up to the dilution 1 : 1 28 (3.36 mg/ml) , while the fungicide activity of 1 0:90 mixture was proven at the minimum concentra­tion of 0.42 mg/ml .

For the c linical isolate of dermatophyte Trichophy­ton mentagrophytes, a higher concentration was needed for the fungicidal effect; the 40:60 mixture was fungicidal in minimal concentration of 2 1 5 mg/ml . Isopropylmiristate, which was used as a solvent for dilution of essential oils, did not exhibit any growth inhibition effects on tested microorganisms.

3.2 Microencapsulation of Animal Repellents for Agricultural Textiles

The main purpose of microencapsulating volatile animal repel lents was to prolong their activity by slow diffusion through microcapsule wal ls . To achieve partly permeable microcapsule walls, process parame­ters had to be modified. An example of in situ polym­erisation microencapsulation parameters for the prepa­ration of Daphne repellent microcapsules in a 1 0 L reactor is given in Table 2 .

Agricultural field testing showed a good repel ling effect against deer and rabbits for both formulations of nonwoven textile strips i mpregnated with microencap­sulated repellent Daphne. The results are given i n Table 3 and Fig. 7 .

1 0 .. _ . __ .. _.-... _ . ..••. ..•.• .• .•• _ .•..• _- ·-7--·-·- ·------- - Control ( F I ) :

� _ 20glm2 l F I ) .;;, � " ---co _ 30glm2 ( F I )

ti 7 � - - - - Control (F2) c .. 6 +------------+----.-'-.---+--� .;;, _ 20glm2 (1'2) � 5 .. __ 30glm2 (F2) � 4 ... � = � " .0 E 2 = Z 1 ""

0

o 6 10 12 14 In 1 8 20 22 Oays of uP' rim e n I

Fig. 7-Test results of nonwoven textiles i mpregnated with micro· encapsulated deer and rabbit repel lent Daphne on two agricultural fields ( F I and F2) with two textile formulations (impregnation 20g/m2 and 30g/m2), compared to control baits with no repellent

Table 2- Main parameters of in situ polymerisation micro­encapsulation of Daphne repellent in a 10 L reactor

Parameter Value

Melamine-formaldehyde 1 1 gl I �Og of core material prepolymer

Modifying agent/microcapsule core 6.5 g/ l OOg of core material

Diameter of dissolver plate

Mixing speed

Emulsification t ime

Share of dispersed phase in emulsion

Polymerisation time

Polymerisation temperature

80 cm

1 500 rpm

20 min

35 vol. %

90 min

75°C

Table 3-Animal repellent efficacy of nonwoven textiles impregnated with microencapsulated repel lent Daphne-Field testing against deer and rabbit

[Test location: Field 1 and Field 2; 1 0 apple branches per bait; Test sample: Nonwoven polypropylene strips (3 m long. 5 cm wide); and Impregnation with microcapsule suspension: 20g/m

2 and 30g/m

2)

Evaluation day of experiment

o 2

4

8

10

13

18

22

Control (Untreated)

o

2

3

1 0

1 0

1 0

Number of damaged branches per bait (maximum 1 0) Field 1

Impregnated textile 20g/m2 30g/m2

0 0

0 0

0 0

2 0

2 0

4 0

5 0

1 0 8

Control (Untreated)

0

0

0

3

5

5

7

8

Field 2 Impregnated textile

20g/m2

30g/m2

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0

BOH & KNEZ: MICROENCAPSULATION OF ESSENTIAL OILS & PHASE CHANGE MATERIALS 79

Table 4--- Main process parameters for the preparation of PCM microcapsules in a JO L reactor

Parameter

Fil l ing

Amount of PCM in emulsion (microcapsule core)

Value

7 - 1 0 L

25 - 40%

Conc. of modify ing agent 4 - 6.5%

Conc. of prepolymer (micro- 1 8 .5 - 40 gi l 00 mL of microcap-capsule wall material) sule core material

Stirrer diameter

Mixing speed

90 mm

1 000 - 2000 rpm

Table 5- Characteristics of four bathes of m icrocapsules containing PCMs with the melting point of 25 "C, 28 "C, 40 "c

and 50 "c

Parameter Value

Melting point of PCM i n 2 5 2 8 40 50 microcapsule core, °C

Mix ing speed during emul- 1 500 1 500 1 900 1 500 sification, rpm

Av. d iameter of microcap- 9. 1 0 8.30 7 .86 8.63 sules, llm

Av. thickness of microcap- 0. 1 4 0.22 0. 1 5 0. 1 7 sule wal l, Ilm

M icrocapsule suspension 37.0 38.2 39.5 36.4 dry matter, %

M icrocapsule suspension 300 425 300 470 viscosity at 25 °C (Brookfield), mPas

Microcapsule suspension 7.0 7.6 7 .7 7 .3

pH

3.3 Microencapsulation of PCMs for Textile Applications

To remain functional over numerous phase transi­tion cycles, microencapsulated PCMs have to remain encapsulated within the impermeable microcapsule walls for the whole product l ife. PCM microcapsules needed to be highly resistant to mechanical and ther­mal stress, which was achieved by the modifications of microencapsulation process .

In in situ polymerisation of amino-aldehyde resins, all materials for the microcapsule wall originate from the continuous (aqueous) phase, and therefore have to be water soluble. Under ideal conditions, by the change i n pH or temperature all mass of the wall mate­rial precipitates and distributes evenly over the sur­faces of droplets in emulsion (future microcapsule cores). This results in a uniform microcapsule wall thickness, regardless of the microcapsule size.

Fig. 8-Scanning electron micrograph (magnification x 8000) of m icroencapsules (3-6 11m diameter) contain ing paraffin ic PCMs, obtained after the spray dry ing of the microcapsule suspension

Better process control and improved mechanical properties of PCM microcapsules were achieved pri­marily by the selection and optimisation of a combi­nation of wall prepolymer (partly methylated trimeth­ylolmelamine) and the modifying agent (styrene­maleic acid anhydride copolymer with the molecular weight of 350.00 g/mol) , which had a double func­tion of being an emulsifier and a poly condensation i nitiator for melamine-formaldehyde precondensates. At optimum conditions, polymerisation evenly devel­oped at the surface of the emulsified PCMs, thus forming an impermeable microcapsule wal l .

The process parameters for the microencapsulation of PCMs in a l OL reactor are given in Table 4, and the characteristics of microcapsules containing PCMs as the core material are l isted in Table 5. The process en­abled the production of microencapsulated hydrocar­bon PCMs with mechanically and thermally stable amino-aldehyde walls and narrow particle size distri­bution (Fig. 8). By regulating the ratio of entering raw materials, it was possible to change the properties of microcapsule walls as well as to regulate the dry mat­ter content, pH and viscosity of the final microcapsule suspensions.

4 Conclusions Microencapsulation of antimicrobial essential oils,

animal repellents and PCMs for textile applications has been described. In all three cases, a modified in situ polymerisation method was used for the prepara­tion of synthetic polymeric walls . However, process parameters had to be modified and adjusted to achieve different release mechanisms. I n the case of volatile

80 INDIAN J. FIBRE TEXT. RES., MARCH 2006

animal repellents, essential oi ls needed to be slowly released from the microcapsule core by diffu­sion/evaporation, to achieve a prolonged release; therefore the microcapsule wall had to be partially permeable. The main goal of microencapsulating an­timicrobial essential oi l s for textile shoe insoles was to achieve a targeted release during walking and no re­lease when the shoes were not worn . Microcapsule walls had to be impermeable and pressure-sensitive. In the case of microencapsulated PCMs, in addition to impermeabi lity, an improved mechanical resistance of microcapsule walls was needed to assure a sufficient mechanical strength to withstand solid-liquid trans i­tions of microcapsule core without leaking. Main pro­cess modifications to reach the desired microcapsule characteristics were based primari ly on the selection and ratio of melamine-aldehyde prepolymers and of a styrene-maleic acid anhydride copolymer modifying agent, as well as on the determination of emulsifica­tion and polymerisation parameters (rpm, temperature, duration) . Experiments in a t OL reactor showed that for each core material , process parameters had to be empirically optimised to ach ieve the desired charac­teristics.

Acknowledgement The authors are thankful to the Siovenian Ministry

of Education , Science and Sport; and Aero Chemical, Graphic and Printing I ndustries for financial support. They are also thankful to Mr Vojko Skerlavaj of Agri­cultural Institute of Slovenia for conducting part of agriculture testing.

References I Boh B & Kardos D, in Microspheres, Microcapsules alld

Liposollle.l' : Microcapsule Palems allli Producls, Vol. 6, edited by R Arshady and B Boh (Citus Books, London, UK), 2003, 47.

2 Boh B, Knez E & Staresinic M, in Microspheres, Microcap­sules alld Liposollles, : Microcapsule Paleills and ProduCls, Vol. 6, edited by R Arshady and B Boh (Citus Books, Lon­don, UK), 2003, 235 .

3 Goorhuis H, DE Pat 2 1 6 138 1 (to Sandoz), 1 3 Ju ly 1 972. http://ep.espacenet.com .

4 Imada K, Sueda Y, Abeta S & Yamada E, Jap Pal 48092665 (to Sumitomo), December 1 973. http://ep.espacenet.com .

5 Totoki C, Jap Pal 49036985 (to Totoki C) , 5 April 1 974. http://ep.espacenet.com.

6 Ikeda K, Sato M & Kato H, Jap Pat 49 1 2802 1 (to Toa Go­sei) , 7 December 1 974. http://ep.espacenet.com.

7 Moore R F & Schi l ler F C, US Pal 38 1 7773 (to National Cash Register), 18 June 1 974. http://ep.espacenet.com.

8 Oshiage K & Takabayashi T, Jap Pat 50067778 (to Sakai Textile), 6 June 1 975. http://ep.espacenet.com.

9 Oshiage K & Takabayashi T, Jap Pal 50065678 (to Sakai Textile), 3 J une 1975. http://ep.espacenet.com.

1 0 Bartlett J R & Shinner C , DE Pal 2444 140 (to Dickinson Robinson), 20 March 1975. http://ep.espacenet.com .

I I Oshi age K & Kubo M, Jap Pat 5 1 1 23379 (to Nippon Kayaku), 28 October 1 976. http://ep.espacenet.com .

1 2 Nakano T & Sakaoka K , Jap Pat 53042833 (to Hayashi Ka­gaku Kogyo), 1 8 Apri l 1978. http://ep.espacenet.com.

13 McBride D T & Godfrey T E, Eur Pat 0202856 ( to Mi l l i ken Research), 26 November 1986. http://ep.espacenet.com.

14 Gomes J I N R & Genovez M C & Hrdina R, Texl Res J , 67 ( 1 997) 537.

1 5 Okuyama H , Ishimaru S & Asano N , Jap Pat 49 133682 (to Seiren), 23 December 1974. http://ep.espacenet.com.

1 6 Okuyama H, Ishimaru S & Asano N , Jap Pat 5 10 1 2755 (to Seiren), 3 1 January 1 976. http://ep.espacenet.com.

1 7 Kiri tani M , J P Pat 5 1070379 (to Fuji Photo Film), 1 7 June 1 976; http://ep.espacenet.com.

18 1 8 M ihara Kogaku & Gijutsu K K, Jap Pal 58030435 (to M ihara Kogaku Gijutsu), 22 February 1 983. http://ep.espacenet.com.

19 Hare D S & Wi l l iams S A, WO Pat 99259 17 (to Foto Wear), 27 May 1 999. http://ep.espacenet.com.

20 Hare D S & Wi l l iams S A, WO Pat 9926 1 1 1 (to Foto Wear), 27 May 1999. http://ep.espacenet.com.

2 1 Ruggeri C, GS Pal GB2 1 16578 (to Ruggeri C), 28 Septem­ber 1 983. http ://ep.espacenet.com .

22 Kito T, Matsunami N, Nakasuj i K & Shibahashi Y, Jap Pat 62 1 56355 (to Pi lot I nk), I I Ju ly 1 987. http://ep.espacenet.com.

23 Shibahashi Y, Nakasuji N , Kataoka T, [nagaki, H, Kito, T, Ozaki, M, Matunami N, Ishimura N & Fuj i ta K, DE Pat 3602805 ( to Pilot Ink), 3 1 July 1986. http://ep.espacenet.com.

24 Kamata M , Sasaki 0, Suefuku S & Maeda T, Eul' Par 04801 62 (to Matsui Shikiso), 1 5 Apri l 1 992. http://ep.espacenet.com.

25 Ttigawa Y, Hoshikawa R, Jap Pal 7 10968 1 (to Matsui Shikiso), 25 Apri l 1995. http://ep.espacenet.com.

26 Aitken D, B urkinshaw S M & Towns A D, Rev Prog Color Relat Topics, 26 ( 1 996) 1 .

27 Furuta T, Tanaka M & Mitani K, Jap Pal 62289684 (to Unit ika), 16 December 1 987. http://ep.espacenet.com.

28 Nakanishi M, Iwasaki T & Maeda S, WO Pat 8905335 (to Japan Capsular Products & Mi tsubishi Kasei), 1 5 June 1989. http://ep.espacenet.com .

29 Iwasaki T & Maeda S, Jap Pat 2 1 1 0 1 73 (to Japan Capsular Products & Mi tsubishi Kasei), 23 Apri l 1990. http://ep.espacenet.com .

30 Kamata K, Kitagawa Y & Hoshikawa R, Jap Pal 62 1 2579 (to Matsui Shikiso), 2 August 1 994. http://ep.espacenet.com .

3 1 Kitagawa Y & Hoshikawa R , GS Pat 2270321 {to Matsui Shikiso), 9 M arch 1 994. hnp://ep.espacenet.com.

32 Yabuchi N, Mizuguchi K & Ish i i K, Jap Pat 7 1 59924 (to Nipppon Paint), 23 June 1995. http://ep.espacenet.com .

33 Pantsyrnyj V I, Porotikov N V, Shchegolkova A L. B i ryukova L A, Kudryavtsev V F & Shevchenko A V , RU

Pat 2095836 (to Vojskovaya Chast), 1 0 N ivember 1 997. http://ep.espacenet.com .

BOH & KNEZ: MICROENCAPSULATION OF ESSENTIAL OILS & PHASE CHANGE MATERIALS 8 1

34 Sekar N, CO/all rage , 45 ( 1998) 39. 35 B irjukova L A, Porotikov N V . Kudrjavtsev V F &

Shevchenko A V, RU Pat 2 1 39900 (to Vojskovaya Chast), 20 October 1 999. http://ep.espacenet.com.

36 Pandel l N W & Temin S C, US Pat 3632296 (to Cluett Peabody), 4 January 1 972. http://ep.espacenet.com.

37 Fornel l i S, Mellialld Text fllt , 2 ( 1996) 1 08. 38 Ida S & Hosokawa K. DE Pat 204 1 899 (to Kanegafuch i

Spinning), 1 8 March 1 97 1 . http://ep.espacenet.com. 39 Nish ij ima Y & Shimizu K, DE Pat 2 1 64 1 89 (to Kanega­

fuch i Spinning & Snia Viscosa Societal, 3 march 1 972. http://ep.espacenet.com.

40 Nakayama S, DE Pat 6 1 042024 (to Matsumoto Yushi Sei ­yaku), 28 February 1 986. http://ep.espacenet.com.

4 1 Teuschler H J & Hucke H . DE Pat 430 1 992 (to Tech In), 24 June 1 993. http://ep.espacenet.com.

42 Teuschler H J. DE Pat 424 1 96 1 (to Tech In), 24 June 1 993. http://ep.espacenet.com.

43 Teuschler H J, DE Pat 4300390 (to Tech Wissenschaftl iche Gesellschaft), I July 1 993. http://ep.espacenet.com.

44 Zubkova N S, Fibre Chelll, 29 ( 1 997) 1 26. 45 Kovar R F, Farrel B, Tiano T, Levi R & Harpel J W H, Re­

cellt Adv Flame Retard Polym Mater, 8 ( 1997) 88. 46 Antonov A, Potapova E, Rudakova T, Reshetnikov I, Zubk­

ova N, Tuganova M & Khalturinskij N, Spec Publ R Soc Chelll, 224 ( 1 998) 290.

47 Zubkova N S. Butylkina N G, Chekanova S E, Tyuganova M A, Khalturinskii N A. Reshetnikov I S & Naganowski Y K, Fibre Chem, 30 ( 1 998) I I .

48 Sroka P. DE Pal 2460855 (to Hermann Windel), 24 June 1 976. http://ep.espacenet.com.

49 Groshens P & Paire C, FR Pat 2625745 (to Lainerie de Picardie), 13 July 1 989. http://ep.espacenet.com.

50 K ishi S, lap Pat 57 1 88435 (to Meisei Rej inokara), 19 No­vember 1 982. http://ep.espacenet.com .

5 1 Sogabe Y & Harada K , lap Pat 1 985, 601 49642 (to Achi l ­les), 7 August 1 985. http://ep.espacenet.com.

52 Sato H. lap Pat 633589 1 (to Bando Chemical), 6 December 1 994. http://ep.espacenet.com.

53 Hohara K, Kamo M, Shiraki H & N ihei N, lap Pal 6273940 (to N ippon Kako Seish i ) , 30 September 1 994. http://ep.espacenet.com.

54 Walter D & Linke H, DE Pat 1 6920 1 4 (to Henkel), 20 April 1 972. http://ep.espacenet.com.

55 Van Kampen D M & Nee Rozzo F R, US Pat 3723327 (to Lever Brothers), 27 March 1 973. http://ep.espacenet.com.

56 Hachmann K. Boeck A, Jakobi G & Jung D, DE Pal 241 3561 (to Henkel), 2 October 1 975. http://ep.espacenet.com .

57 Markussen E K & Schmidt A W, US Pat 4 1 0699 1 (to Novo lndustri). 15 August 1 978. http://ep.espacenet.com.

58 Onoda T, Sugai H & Sekiguchi K, lap Pat 63 1 05098 (to Showa Denko), 1 0 May 1 988. h ttp://ep.espacenet.com .

59 Kamel A, Hurckes LC & More l l i M M , US Pat 49 1 984 1 , (to Lever Brothers), 24 April 1 990. http://ep.espacenet.com.

60 Olson K E, US Pat 49650 1 2 (to Olson KE), 23 October 1 990. http://ep.espacenet.com.

6 1 Coyne T S, England J B , Haendler B L , Mi tchell F E, Steichen D S & Johnson C L, US Pat 509302 1 (to Clorox), 3 March 1 992. http://ep.espacenet.com.

62 Lykke M & Mistry K K, Simonsen 0, Symes K C, WO Pat 9724 1 77 (to Novo Nordisk), 1 0 July 1 997. http://ep.espacenet.com.

63 Briggs B, US Pat 3666680 (to Prurex), 30 May 1 972. http://ep.espacenet.com.

64 Weber R & Opgenoorth A, DE Pat 204833 1 (to Henkel), 6 Apri l 1 972. http://ep.espacenet.com.

65 Weber R & Arends D, DE Pat 2 1 04975 (to Weber & Arends), 1 4 September 1 972. http://ep.espacenet.com.

66 Kranz H, DE Pat 2 1 4 1 280 (to Henkel), I march 1 973. http://ep.espacenet.com.

67 Hachman K, Sperling G & Puchta R, DE Pal 253573 1 (to Henkel), 26 February 1 976. http://ep.espacenet.com.

68 Christidis Y & Diery H, DE Pat 2535 1 83 (to Nobel Hoechst), 1 5 April 1 976. http://ep.espacenet.com.

69 Alterman D S & Chun K W, US Pat 3983254 (to Lever Brothers), 28 September 1 976. http://ep.espacenet.com.

70 Alterman D S & Chun K W, GB Pat 1 509797 (to Uni lever), 4 May 1 978. http://ep.espacenet.com .

7 1 Mazzola L R. US Pat 4078099 (to Lever Brothers), 7 March 1 978. http://ep.espacenet.com.

72 Brichard J, Eur Pat 0030759 (to Interox), 24 June 1 98 1 . http://ep.espacenet.com.

73 Chun K W, Lang D J & Santos E, US Pat 4655780 (to Lever Brothers), 7 Apri l 1 987. http ://ep.espacenet.com.

74 Corring R & Gabriel R, US Pat 5 14 1 664 (to Lever Broth­ers), 25 August 1 992. http://ep.espacenet.com.

75 Uni lever, NL Pat 6904622 (to Uni lever), I October 1 969. http://ep.espacenet.com.

76 Dow Corning, FR Pat 2354382 (to Dow Corning), 6 Janu­ary 1 978. http://ep.espacenet.com.

77 Reuter H & Saran H, DE Pat 3 12863 1 (to Henkel), 3 Febru­ary 1 983. http://ep.espacenet.com.

78 Schneider H, DE Pat 1 287246 (to Werner und Mertz), 1 6 January 1 969. http://ep.espacenet.com.

79 Grimm J E, US Pat 3896033 (to Colgate Palmolive), 22 July 1 975. http://ep.espacenet.com.

80 Sch i l l ing K J, DE Pat 2653259 (to Procter and Gamble), 2 June 1 977. http://ep.espacenet.com.

8 1 Pracht H J & Iding S H, DE Pat 26323 1 8 (to Procter and Gamble), 1 7 February 1 977. http://ep.espacenet.com.

82 M unteanu M, Cseko C, Oltarzewski E S, Lindauer J I & Withycombe D A, US Pat 4446032 (to International Flavors and Fragrances), 1 May 1 984. http://ep.espacenet.com .

83 Claus A D, Culver G E, Piatt D M & Wierenga T J, ELlr Pat 0269 1 79 (to Procter and Gamble), I June 1 988. http://ep.espacenet.com.

84 N imrick T L Br Pat 9004492 (to Procter and Gamble), 1 0 September 1 99 1 . http://ep.espacenet.com.

85 De Felice I, GB Pat 140 1 1 43 (to Eurand), 16 July 1 975. http://ep.espacenet.com.

86 Brain D K & Cummins. M T, DE Pat 2653329 (to Procter and Gamble), 2 June 1 977. http://ep.espacenet.com.

87 Shibata Towel K K, lap Pat 58004886 (to Shibata Towel) , 12 January 1 983. h ttp://ep.espacenet.com.

88 Ono H & Tokuoka S, lap Pat 1 26628 1 (to Kanebo), 24 October 1 989. http://ep.espacenet.com.

89 Ono H & Tokuoka S, lap Pat 1 266282 (to Kanebo), 24 October 1 989. http://ep.espacenet.com.

90 Kanebo, lap Pat 2264080 (to Kanebo), 26 October 1 990. http://ep.espacenet.com .

82 INDIAN J . FIBRE TEXT. RES., MARCH 2006

9 1 Ono H, Nunoo T , M udagami S , Yamauchi T & Omori A, lap Pat 20550 1 0 (to Kanebo), 23 February 1 990. http://ep.espacenet.com .

92 Ono H & Tokuoka S, lap Pat 3064504 (to Kanebo). 1 9 March 199 1 . http://ep.espacenet.com.

93 Nishigami H, lap Pal 3076875 (to Kanebo), 2 Apri l 1 99 1 . http://ep.espacenet.com.

94 Okumura K. Kamyama S, Murata S, Kawada K, Kubota M & Azuma M, lap Pat 6 1 1687 1 , (to Osaka Juki) , 24 Apri l 1 994. http://ep.espaceneLcom.

95 Sano J & Une T. lap Pat 6228880 (to Kanebo). 16 August 1 994. hllP://ep.espacenet.com.

96 Shirakawa Y, lap Pat 1 0236903 (to Union Kagaku), 8 September 1 998. hnp:llep.espacenet.com.

97 Saito Y. lap Pat 3206003 (to Hosokawa Textile), 9 Sep­tember 1 99 1 . hllp:llep.espacenel.com.

98 Umibe H, Hario S & Inoue S, lap Pat 3090682 (to To­yobo), 1 6 April 199 1 . hllp:llep.espacenel .com.

99 I noue S, Hario S & Umibe H, lap Pat 3 148203 (to To­yobo), 25 June 1 99 1 . http://ep.espacenel.com.

100 Ogawa Y, Mutagami S & Yamauchi T, lap Pat 3 1 27701 (to Kanebo), 30 May 1 99 1 . htlp:llep.espacenel.com.

1 0 1 Saito Y & Nakamura M. lap Pat 3002 10 1 (to Hosokawa Texti[e), 8 January 1 99 1 . http://ep.espacenet.com.

102 Boh B. Kosir I, Knez E, Kukovic M . Skerlavaj Y & Skvarc A, 1 Microencapsulation. 1 6 ( 1999) 1 69.

103 Mi tsuyoshi A, Miura H & Hatada T, lap Pat 63256769 (to Toray), 24 October 1 988. http://ep.espaceneLcom.

104 Takeda K, Kawai F & Amano J , lap Pat 06299466 (to To­ray), 25 October 1 994. http://ep.espacenel.com.

105 Katsuya J & Azumaguchi K, lap Pat 2084595 (to Tokyo Hou[aisha), 26 March 1 990. http://ep.espaceneLcom.

106 Katsuya J & Azumaguchi K, lap Pat 208450 [ (to Tokyo Houlaisha), 26 March 1990. http://ep.espacenet.com .

1 07 Kuramoto N &Hiroshima M, lap Pat 4 1 00980 (to Ashai). 2 April 1 992. hllp:llep.espacenel.com .

108 Jorda R, Autant P & Rossin R, Eur Pat 0576377 (to Flamel Technologies), 29 December 1 993. hllp:llep.espacenet.com.

1 09 Boh B. Hodzar 0, Knez E, Kukovic M, Pipal Y & Yoda K, Proceedillgs, Zb Ref Posvetovallja Siov Kell1 Dnevi (Fa­kulteta za kemijo in kemijsko tehnologijo), 1 999, 762.

1 1 0 Okamoto H, Inoue S, Miyamatsu H & Yoshida K, Jap Pat 2000 1 1 9 106 (to Erubu K K ), 25 April 2000. http://ep.espacenet.com.

I I I Murata T, lap Pat 4 1 08728 (to Kanebo), 9 Apri l 1 992. hllp://ep.espacenel.com.

1 1 2 Toshikazu F, Yoshikatsu M & Kyoji M. US Pat 5232769 (to Kanebo), 3 August 1 993. http://ep.espacenet.com.

1 1 3 Haruta M, Takahashi T & Saito K, lP Pat 9296367 (to To­ray), 1 8 November 1 997. http://ep.espaceneLcom.

I [ 4 Dim S A, Fr Pat 2780073 (to Dim S A), 24 December 1999. http://ep.espacenel.com.

1 1 5 Lapidus 0, Brault 0, Lognone Y, Richard J, Benoit J P & MOrleau S, WO Pat 0005446 (to Ted Lapidus), 3 February 2000. http://ep.espacenel.com.

1 16 Cowsar 0 R, US Pat 420 1 822 (to US Dept of the Army), 6 May 1 980. http://ep.espacenet.com.

1 1 7 lchinukizaka I, lap Pat 62 1 068 1 4 (to Kanai Hiroyuki ), 1 8 May 1 987. http://ep.espacenel.com .

1 1 8 lchinukizaka I, lap Pat 5054364 (to Kanai Hiroyuki), 5 March 1 993. http://ep.espacenet.com.

1 1 9 Kiyokawa H. lap Pat 53 1 1 579 (to Kiyokawa H), 22 No­vember 1 993. http ://ep.espacenet.com.

1 20 Bryant Y & Colvin D, US Pat 4756958 (to Triangle Re-search and Development). 12 July 1 988. http://ep.espacenet.com .

1 2 1 Sengupta S , US Pat 5007478 (to University o f Miami) . 1 6 Apri l 1 99 1 . http://ep.espacenet.com.

1 22 Bryant Y & Colv in D, US Pat 536680 1 (to Triangle Re: search and Development), 22 November 1 994. http://ep.espacenel.com.

1 23 Bryant Y & Colv in 0, US PaT 5499460 (to B ryant Y & Colvin 0), 1 9 March 1 996. http://ep.espaceneLcom.

124 B ryant Y & Colv in 0, US Pat 5637389 (to B ryant Y & Colvin D), 10 June 1 997. http://ep.espacenet.com.

1 25 Buckley T, US Pat 5722482, (to B uckley T), 3 March 1 998. http://ep.espaceneLcom.

1 26 Salyer I, US Pat 5885475 (to Dayton University), 23 March 1 999. http://ep.espacenel.com.

1 27 B uckley T, US Pat 6004662 (to B uckley T), 2 1 December 1999. http://ep.espacenel.com .

1 28 Nuckols M, Hughes R, Grupe C & Fitzgibbon S, US Pal 6 1 20530 (to US Secretary of Navy), 19 September 2000. http://ep.espacenet.com.

1 29 Pause B , US Pat 6077597 (to Outlast Technologies), 20 June 2000. http://ep.espacenel.com.

1 30 B arker E, Gay B & B renner J, US Pat 604 1437 (to B arker E, Gay B & B renner J), 28 March 2000. http://ep.espacenet.com.

1 3 1 Holman M , US Pat 6099894 (to Frisby Technologies), 8 August 2000. http://ep.espacenet.com.

1 32 Painter R, WO Pat 0065 1 00A I (to Painter R), 2 November 2000. http://ep.espacenet.com.

1 33 Shim H, Mccul lough E A & Jones B W, Text Res l, 7 1 (200 1 ) 495 .

1 34 Knez E, SI Pat 84 1 1 3 1 9 (to Aero Chemical Graphic and Paper Industry), 3 1 December 1 995. http://ep.espacenet.cOlnl.

135 Kukovic M & Knez E, Eur Pal O 782 475 (to Aero Chemi­cal Graphic and Paper Industry). 9 July 1 997. htlp:llep.espacenel.com/.

1 36 Boh B , Kos i r I, Knez E, Kukovic M, Skerlavaj Y & Skvarc A, Int 1 Pest Manage, 45 ( 1 999) 297.