Wadsö, Lars

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LUND UNIVERSITYPO Box 117221 00 Lund+46 46-222 00 00An example of a microcalorimetric solid state compability testWadsö, Lars1998Link to publicationCitation for published version (APA):Wadsö, L. (1998). An example of a microcalorimetric solid state compability test. (Report TVBM (Intern 7000-rapport); Vol. 7127). Division of Building Materials, LTH, Lund University.Total number of authors:1General rightsUnless other specific re-use rights are stated the following general rights apply:Copyright and moral rights for the publications made accessible in the public portal are retained by the authorsand/or other copyright owners and it is a condition of accessing publications that users recognise and abide by thelegal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private studyor research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portalRead more about Creative commons licenses: https://creativecommons.org/licenses/Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will removeaccess to the work immediately and investigate your claim.LUND UNIVERSITYLUND INSTITUTE OF TECHNOLOGYDivision of Building MaterialsAn example of a microcalorimetricsolid state compatibility testLars WadsöRapport TYBM-7127Lund, 1998An example of a microcalorimetricsolid state compatibility testBuilding Materials, ffiiil*.sity, Lund , SwedenIntroductionIf two materials are compatible they do not degrade each other. This is an extremelyimportant aspect of product development as incompatible materials loose their desiredproperties earlier than necessary. Compatibility testing may be used for:. explosives and packaging materialso fuels and polymer containers. foods and packaging materialso many-component washing powderso other reactive products like sealants and adhesives, and proposed packaging materialsA complication in compatibility testing of solid materials is that it is difTicult to bring twosolids together in a reproducible way. It is important to divide the solids as much as possibleto increase the contact surfaces between the materials. Mixing, grinding and pressing are threeways of further increasing the contact.Compatibility tests may often be done in simple closed glass ampoules. Only in cases whereone wants to simulate more complex situations, e.g. the continuos removal of a reactionproduct or a high oxygen concentration, will one need to use a flow-through system.Here I describe a compatibility test between a hydrogen peroxide producing bleaching agentand two different types of papers. One of the papers had been impregnated with a copper saltas copper is a well-known catalyzer of hydrogen peroxide degradation; "The presence ofheavy metals (such as Fe and Cu) in hydrogen peroxide can increase the rate òfdecomposition by many orders of magnitude..." (Kirk and Othmer) This type of measurementis of practical interest to producers of bleaching agents and manufacturers of washingpowders, but is given here as it was developed for a student experiment in isothermalmicrocalorimetry.Method and materialsAn house-hold "percarbonate" bleaching powder was used. This consisted of quite pureNazCO¡ 1.5 HzOz (it also contains some enzymes and already reacted percarbonate). Threeglass ampoules (3 ml) were ha-lÊfilled with approx. 1.5 g of bleaching powder. To two ofthese was added approx. 4 cmz of two types of papers (À and B), each òut into pieces approx.2 mm x 4 mm. The ampoules were then closed and the samples were mixed by shaking.Before the ampoules were entered step-wise into the TAM microcalorimeter (ThermometricAB, Järfälla, Sweden) care was taken so that the paper was as evenly distributed in thepowders as possible. Baselines were measured before and after the measurement with sealedglass ampoules half-filled with water. The measurements were made at +40oc.Two papers were used. Paper A was an ordinary brown packaging. Paper B was the samepaper which had been impregnated with an aqueous solution of CuSOq. The copper content of¡the paper was 1.5 mglcm2 of CuSO¿'5 HzO or 0.4 mg/cm2 of Cu. The paper in each ampoulecontained approx. 2 mg copper.Result and discussionThe thermal power measured for the ampoules with only bleaching agent was in the order of5 pW. A slightly higher value was found for the sample with the untreated paper A. Figure Ishows the results. The effect of the copper was quite remarkable. Already when the ampoulehas just come down to the measuring position (less than t hour after the paper and thepercarbonate were mixed) a thermal power of 45 ¡rW is measured. During the 20 h measuringperiod this increases to nearly 70 ¡rW. The compatibility problems between the percarbonateand paper B containing copper is thus clearly demonstrated.7060ãsoL.940&ã30¡rÊ20l0020Figure 1. Examples of results from three experiments with percarbonate-paper compatibility.Solid line: only percarbonate; dashed line: percarbonate and paper A; dash-dotted line:percarbonate and paper B. All samples contained 2 g percarbonate.A more quantitative discussion of stability and compatibility should be based on anunderstanding of the chemical process responsible for the degradation of the bleaching agentNazCO¡ l.5HzOz --> NazCOr + l.5}lzOz --> NazCO¡ + l.5HzO + 312 OzÂH of the first reaction is assumed to be small compared to the ÂH of the second reactionwhich is large: ÂH:-95 kJ/mol: -500 J/g.If we assume that a degradation process is not autocatalytic, i.e. the reaction products do notcatalyze further degradation, then the degradation can be modeled as a first order "decay"-process with the following equations:0 5 10time / h15M(t): M(0) exp(-h)k: P(o) / AH / M(o)Here P is the thermal power, M is the mass of percarbonate used in the measurement, and k isthe rate constant. The fractional degradation (D) during a time period t may be calculated as:D : 1 - M(t) /M(0) : exp( P(0) t I Nl, I M(0) )For the percarbonate without paper and with paper A approx. 20o/o of the percarbonate isdegraded peÍ yeaÍ, but for the sample mixed with paper B the same figure is 93Yo.It is thusclear that paper B is not a good material to use together with the percarbonate, e.g. in apackage.The above equations should be used with caution as many solid-state processes are auto-catalytic and will accelerate with time. The process here may speed up as the water producedmay increase the mobility of the copper and also generally increase the rate of thepercarbonate reaction.ConclusionThis report describes a quite straightforward testing of the compatibility between a bleachingagent and different types of papers. The method is sensitive to even low-rate degradation andcan be used as a method to screen and test product combinations.March 1 998

An example of a microcalorimetric solid state compability test

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An example of a microcalorimetric solid state compability test

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