fluorination for high barrier

THE ECONOMIC TIMES POLYMERS • APRIL - MAY, 2008 19

CMYK

C O V E R S T O R YC O V E R S T O R Y

FOCUS

IntroductionHigh density polyethylene/polypropylenegranules have been successfully used in rigidcontainers as an efficient material for packingproducts from various industries and it hasbeen a preferred material of choice fordevelopment of new products or in conversionof existing products packed in materials otherthan plastics. Unlike other materials e.g. metalsand glass etc., HDPE has all the conveniencesand efficiency in terms of light weight, lowcost, high stress crack resistance [ESCR], havinghigh drop impact strength, tremendousflexibility in processing/designing, someprotection against moisture, solvents andgases. The only area where polyethylene/polypropylene has a drawback against metalor glass container is in the products wherepermeation and scalping is a problem. Theproducts which typically, presently are notpacked in HDPE/PP or should not be packedin HDPE/PP would be chemicals ranging indifferent fuels, brake fluids, solvents, solventbased formulations, fuel additives, flavours andfragrances to name a few.

To overcome this drawback, HDPE / PPrigid containers are treated with fluorine gasto form High Barrier Fluorinated PlasticContainers.

Principle of Fluorination ProcessFluorination of plastics is basically a surface

modification process, which result in thesubstitution of hydrogen molecules byfluorine molecules, whereby bulk propertiesof fluorine treated plastic container / articleremains unchanged.

The surface fluorination results in changeof the surface properties of polymerdrastically, while the bulk properties of thepolymer remain often unchanged.

Fluorination ProcessThe section of plastic container from off line

Fluorinated plastic containers and componentsFluorinated plastic containers and componentsFluorinated plastic containers and componentsFluorinated plastic containers and componentsFluorinated plastic containers and components

will find various niche applications in thewill find various niche applications in thewill find various niche applications in thewill find various niche applications in thewill find various niche applications in the

packaging of highly permeative, hazardous andpackaging of highly permeative, hazardous andpackaging of highly permeative, hazardous andpackaging of highly permeative, hazardous andpackaging of highly permeative, hazardous and

corrosive chemicals.corrosive chemicals.corrosive chemicals.corrosive chemicals.corrosive chemicals.

Fig. 1: Fluorination Principle

Fig. 2: Schematic Flow diagram of Fluorination Process

High Barrier Solutions

Using Fluorination Process Bhupendra SinghProduct Manager, BloomPackaging Pvt. Ltd., Mumbai

for PlasticContainers

for PlasticContainers

20 THE ECONOMIC TIMES POLYMERS • APRIL - MAY, 2008

CMYK

fluorination process consists of (1 & 5): Afluorinated layer; (2 & 4): A boundarytransition layer and (3): Virgin or untreatedPlastic layer as shown in Fig. 3 from surfaceto inside.

In fluorination process the majority of thechemical reactions occur within this transitionboundary layer and the majority of thephysical and chemical properties such asdensity, refractive index, and chemicalcomposition etc. of the polymer are mainlyonly changed within this layer. The layers canbe schematically represented as shown inFig. 3.

Theory of Solvent Permeation and BarrierFunctionThe Permeability Coefficients (P), which is a

measure of the rate at which a particularsolvent migrates through a polymer, isdefined as

P = D x S

where (D = diffusivity coefficient, S = solubilitycoefficient)

Consider the case of a solvent stored in aplastic container. The permeation of thesolvent through this container takes placedue to the four steps as given in fig. 4.

Hence the permeability rate of liquidsthrough polymeric substrate / container is afunction of various parameters.

The fluorination changes thecharacteristics of the polymer in terms ofpolarity, cohesive energy density and surfacetension. This in turn has a major effect inreducing the wetting, dissolution anddiffusion of non-polar solvents relative tothe polymer as shown in Fig. 5.

Thus, fluorination is effective inminimising the permeability of non polar

solvents through a polymer surface. Sincefluorination modifies only those polymermolecules near the surface, there is nomeasurable change in the mechanicalproperties such as tensile strength and impactresistance.

Measurements of Fluorination LevelFluorination treatment is quantified usingFourier Transformation Infra RedSpectroscopy (FTIR). C-H bond shows peakabsorption at 1440 – 1480 cm-1, while C-F bondgives peak absorbance at 930 – 1320 cm-1.The FTIR of untreated Polyethylene (PE) is asshown in Fig. 6.

As seen in Fig. 6, FTIR of untreated PE showspeak for C-H bond at 1440 – 1480 cm-1, while

Fig. 3: Layers of Fluorine on the Plastic Bottle

1. Wetting of the surfaceby solvent.

2. Dissolution of the solventinto the polymer.

3. Diffusion of Solventthrough polymer

4. De-sorption / Evaporation ofthe liquid through the polymer.

Fig. 5: Cross-Section of fluorinated container wallshowing the surface treatment

The surfacefluorination results inchange of the surfaceproperties of polymerdrastically, while thebulk properties of thepolymer remain oftenunchanged.

Fig. 4: Permeation in a polymer


CMYK

the peak at 930 – 1320 cm-1 for the C-F bondis absent. When polyethylene is treated withfluorine by direct offline fluorination process,it shows one more peak at 930 – 1320 cm-1 forthe C-F bond as shown in the Fig. 7. The levelof fluorination is decided based upon its %transmission ratio, which is a ratio of peakabsorbance of C-F bond and peak absorbanceof C-H bond.

% Transmission Ratio = Absorbance of C-F Absorbance of C-H

As the fluorinationtreatment level is increased, the% Transmission Ratio values alsokeeps on increasing as shownin Fig. 8. Thus fluorinationtreatment is quantified.

It is very difficult to get thesame and exact values for the% Transmission Ratio obtainedby FTIR every time. Hence arange for these values is takenfor the easy under standing ofthe treatment level. This rangeof % Transmission Ratio valueis then represented in the formof values which is defined asthe ‘Level of Fluorination’. Theconversion of range of %Transmission Ratio to Level ofFluorination is as given in TableI.

The fluorinators world wideuses this ‘Level of Fluorination’which helps their customer as aready reference during selectionof the fluorinated containers.Every product requires differentlevel of fluorination as theyrequire different barrierproperties. The customer takesthe fluorinated container basedon his barrier requirement; moreis the barrier requirement ordangerous the chemical, thecustomer goes for higher levelsof treatment. There after acustomer would test thesecontainers for the productcompatibility and stability in thecontainer. After he is satisfiedwith one level of treatment hewill always ask for that level forhis particular product package.

The level of fluorination isthen generally decided by theagreement between thecustomer and the supplier afterthe customer is satisfied that a

Currently the mostaccepted packagingapplications offluorinated plasticcontainers includeinsecticides,herbicides, petroleumbased products likelube oil, petrol,cleaning solvents,automotive additives,penetrating oil,degreasers, paintthinners, essential oiland pine oil.

Transmission Level ofRatio (% T) Fluorination

> 12 5

> 8 & < 12 4

> 6.5 & < 8 3

> 5.5 & < 6.5 2

> 4 & < 5.5 1

Table I: The conversion of % TransmissionRatio to Level of Fluorination.

Fig. 6: The FTIR of untreated Polyethylene (PE)

Fig. 7: FTIR of treated Polyethylene

Fig. 8: FTIR peaks for increasing treatment levels (U – Represents notreatment, 1-5 represents increasing Level of Fluorination)


CMYK

particular level of fluorination is acceptablefor his application.

Permeation TestingThe solvent permeation through containersis generally tested by an Accelerated KeepingTest (AKT) or as per IS: 2798 which involves

high temperature exposure of the filledcontainer over a period of time. Normally,exposure at 500C (+ 10C) for 28 days isconsidered equivalent to 1 year of normalexposure. After 28 days, a comparison of percent weight loss in the treated and untreatedcontainers will provide an indication ofpermeation barrier effectiveness. Table 2 liststhe results of permeation studies performedfor various common chemicals.

The data in Table 2 proves theeffectiveness of Fluorination in reducing thepermeability of hydrocarbon-based solventsin HDPE containers. The above solvents arecommonly used in a majority of industrial,agricultural and household products.

It should be noted that combinations ofcertain chemicals in a specific formulationmay cause a reduction in the effectiveness ofa fluorinated barrier. Therefore, it isrecommended that all formulations bethoroughly tested by the method previouslydescribed prior to the final choice ofpackaging material.

Permeation Test data of Fluorinated PlasticContainersTable 3 gives permeation data for treated anduntreated containers when filled with a wide

Chemicals Untreated Container Fluorinated Container

Cypermethrin 25% EC 32.60 0.25

Endosulphan 35% EC 26.12 0.15

Malathion 50% EC 23.99 0.26

Fenvalerate 20% EC 30.66 0.24

Dicofol 18.5% EC 21.04 0.00

Deltamethrin 28% EC 29.11 0.14

Monocrotophos 36%SL 20.45 0.00

Lacquer Thinner 16.50 3.80

Mineral Spirits 15.07 0.12

2-Stroke Plus Motor Oil 7.10 0.44

Table 3: Permeation Test data for Commercial Products Packaged in HDPE (% Weight Loss)

Solvent Untreated Fluorinated RelativeContainer Container Barrier(% Weight Loss) (% Weight Loss) (Barrier)

Carbon Tetrachloride 28.26 0.05 565

Pentane 98.10 0.21 467

Xylene 42.52 0.21 203

Cyclo-Hexane 22.34 0.15 149

Toluene 61.90 0.52 119

1,3,5 Trimethylbenzene 15.85 0.18 88

1,2 Dichloroethane 11.55 2.89 4

Table 2: Permeation Test Data for Hydrocarbon-based Solvents (as per AKT test)A variety of productswhere problems ofpermeation, corrosionand paneling areobserved in postpacking period, in allthese cases thepossible switch overfrom tin, aluminum orglass to plastic offersother opportunities interms of flexibility ofshapes, closuresystems and printingto the industry.


CMYK

variety of products. As can be observed,Fluorination process reduces the permeationlosses to a great extent thereby ensuring closeconformation of the product specification atthe point and time of use.

Advantages of Fluorinated PlasticContainers

Excellent solvent and moisture resistance.Wide range of aggressive chemicals canbe packed.High barrier fluorinated containers areapproved by CIB (Central InsecticideBoard) for a number of agrochemicals.Can be used for various applications asper IS: 15749 and IS: 8190 (Part 2)amendment no 5 April 2008.

Fluorinated High Barrier Containers areapproved by FDA for Direct Food ContactApplications as per 21 CFR 177.1520 (C).Items 2.1 and 3.1.Advantages of fluorination process isthat it is completely dry process andplastic articles of any shape can betreated, which makes this process moreversatile.

Applications of Fluorinated PlasticContainersCurrently the most accepted packagingapplications of fluorinated plastic containersinclude insecticides, herbicides, petroleumbased products like lube oil, petrol, cleaningsolvents, automotive additives, penetratingoil, degreasers, paint thinners, essential oil andpine oil.

In addition to these, a variety of productswhere problems of permeation, corrosion andpaneling are observed in post packing period,in all these cases the possible switch overfrom tin, aluminum or glass to plastic offers

other opportunities in terms of flexibility ofshapes, closure systems and printing to theindustry.

Packaging of Pesticide, Insecticide,Herbicide ChemicalsFluorinated Plastic Containers are widelyused in packaging of pesticide, insecticideand herbicide chemicals because of veryhigh compatibility with most of thepesticides and insecticides and absence ofcorrosion. Biologically active chemicals arealso packed in modified fluorinated plasticcontainers.

Flavour and Fragrance ApplicationsFood processors find that providing onlythe oxygen barrier is not sufficient, as flavourlosses may render containers unacceptable.Polyolefin’s materials usually lack in oxygenand flavour barrier properties. While theproblem of oxygen barrier may be solvedusing conventional multilayer containers,the flavour still escape through thesecontainers.

Flavours (Food Products) and Fragrances(Non-Food Products) are mixtures of manyvolatile complex organic compounds, usually


CMYK

present in ppm or even at ppb level; whichimpart aroma as well as taste to the foodproduct that we eat.

In such applications fluorinatedcontainers offer excellent flavour barrier fora wide range of flavours. Fluorinated flavourbarrier containers are recommended for usein packaging of vegetable, fruit juice, tea,coffee, spices, and syrup flavours etc. whichrequire very high flavour barrier properties.

Automotive Fuels and Fuel AdditivesFluorinated plastic containers arerecommended for packaging of automotivefuel and fuel additives. The loss of the fuelsuch as petrol, diesel and kerosene is

minimum when they are packed influorinated plastic containers.

Automotive Fuel Tank ApplicationsToday the major commercial application offluorination technology in the developedcountries is for the treatment of HDPEautomotive fuel tanks. These fuel tanks meetthe US federal & EPA requirements ofpermeation loss. Plastic fuel tanks havefollowing advantages:

Plastic fuel tanks are typically 40-50%lighter in weight and are less apt toexplode in the event of fire.These fuel tanks generally have lowerproduction costs and offer greaterfreedom of design,allowing moreefficient utilisationof dead space andthus greater fuelcapacity.

Packaging of Aromatic and Non PolarSolventsFluorinated plastic containers are widely usedworld over in the packaging of aromatic andnon-polar solvents.

Packaging of Inks, Paints and ThinnersFluorinated plastic containers are used in theInks & paints industries for the followingsolvent based applications:

Wood CoatsVarnishSpecial CoatingsThinnersMelamine FinishMarine – PrimersPaint RemoversEpoxy – LacquersPaint AdditivesSynthetic EnamelPaints

ConclusionFluorinated plastic containers andcomponents will find various nicheapplications in the packaging of highlypermeative, hazardous and corrosivechemicals. This technology offers greatflexibility in terms of design and creativityto the end users. The recent applications infuel tank, thinner, petro-product, agro, flavourand fragrance market will provide betteralternative packaging options to therespective industries. With its uniqueadvantages fluorination process can be usedin various innovative packagingapplications.

fluorination for high barrier

Documents