In many in­dus­tri­al branch­es, in­clud­ing food stuffs, phar­ma­ceu­ti­cal and cos­met­ic in­dus­try, hy­giene de­mands are in­creas­ing. Per­son­al pro­tec­tive equip­ment (PPE) in­cludes tex­tiles but also footwear, which has to be cleaned and dis­in­fect­ed, re­spec­tive­ly. Clas­si­cal, wa­ter-based clean­ing meth­ods cause se­ri­ous dam­ages to the footwear or do not yield in ad­e­quate dis­in­fec­tion. Anal­y­sis showed re­mark­able hy­giene deficits due to lack of pro­cess­ing pos­si­bil­i­ties. With the im­ple­men­ta­tion of Eu­ro­pean food hy­giene reg­u­la­tions and di­rec­tives in na­tion­al leg­is­la­tion, e.g. through the Or­di­nance of Food Hy­giene in Ger­many, the HACCP con­cept as well as de­mands on per­son­al hy­giene and work wear in­clud­ing footwear have be­come legal­ly bind­ing. The main focus of this re­search pro­ject was the main­te­nance of pro­tec­tive and safe­ty func­tions against me­chan­i­cal forces and a de­vel­op­ment of a dis­in­fect­ing clean­ing pro­cess for safe­ty shoes with liq­uid CO2. The ad­van­tages of liq­uid CO2 are, that it is not toxic and there is no need for dry­ing after re­pro­cess­ing. The pro­cess­ing of the shoes and shoe com­po­nents was per­formed in a 4-bath-clean­ing-pro­ce­dure in a pilot plant. The clean­ing of ma­te­ri­als in liq­uid CO2 was in­ves­ti­gat­ed with sev­er­al dif­fer­ent ad­di­tives. After a fixed max­i­mum of 25 re­pro­cess­ing cy­cles some ma­te­ri­als e.g. a few leathers did not ful­fil the safe­ty re­quire­ments ac­cord­ing to DIN EN ISO 20344 ff. Break­ing, loss of ten­sile strength or par­tial­ly de­crease of breatha­bil­i­ty were the most de­tect­ed deficits. How­ev­er, some leathers and ar­ti­fi­cial leathers were not al­tered due to the CO2-pro­cess and ful­filled the safe­ty-re­quire­ments also after re­pro­cess­ing. These ma­te­ri­als could be used e.g. for PPE-shoes. Sev­er­al toe-caps con­sist­ing of steel or alu­mini­um showed mod­er­ate cor­ro­sion but still guar­an­teed the safe­ty pa­ram­e­ters. Plas­tic toe-caps ful­filled all safe­ty re­quire­ments. As well, ad­di­tion­al rel­e­vant ma­te­ri­als like for ex­am­ple some lin­ing ma­te­ri­als showed no or very low im­pair­ment due to liq­uid CO2-treat­ment. The ap­pli­ca­tion of dirt ab­sorber ma­te­ri­als and spher­i­cal brush­es im­proved the clean­ing ef­fect of even and low tex­tured ma­te­ri­als enor­mous­ly. Upper ma­te­ri­al has been soiled with fatty, car­bo­hy­drate-con­tain­ing and pro­teina­ceous soils. Fatty and car­bo­hy­drate-con­tain­ing soils could be cleaned with the help of dirt ab­sorber and spher­i­cal brush­es which were in­clud­ed for im­prov­ing the me­chan­i­cal forces. The clean­ing of blood was not sat­is­fy­ing. In order to as­sess the dis­in­fect­ing ac­tion, test items were con­tam­i­nat­ed with rel­e­vant mi­croor­gan­isms (bac­te­ria, yeasts and moulds), ei­ther di­rect­ly or mixed with the above-men­tioned soil­ing. In­ac­ti­va­tion of mi­crobes in liq­uid CO2 de­pends upon the species, the time of ac­tion, and the ef­fect of cer­tain ad­di­tives. Par­tic­u­lar­ly in the pres­ence of blood, re­duc­tion of the pop­u­la­tion of cer­tain mi­croor­gan­isms was found to be es­pe­cial­ly dif­fi­cult. The rate of germ re­duc­tion could be in­creased by the use of var­i­ous ad­di­tives. Hence it is pos­si­ble to de­vel­op a shoe which still shows the es­sen­tial­ly safe­ty re­quire­ments after hy­gien­ic clean­ing in liq­uid CO2. A cat­a­logue of re­quire­ments for the pro­duc­tion of pro­tec­tive and safe­ty footwear has been de­vel­oped.

The IGF-pro­ject 15910 N of the re­search as­so­ci­a­tion Europäische Forschungs­ge­mein­schaft Reini­gungs- und Hy­gien­etech­nolo­gie e.V., Cam­pus Ficht­en­hain 11, D-47807 Krefeld, was sup­port­ed via the AiF with­in the fund­ing pro­gramme „In­dus­trielle Gemein­schafts­forschung und –en­twick­lung (IGF)“ by the Fed­er­al Min­istry of Eco­nom­ic Af­fairs and Tech­nol­o­gy (BMWi) due to a de­ci­sion of the Ger­man Par­lia­ment.

The re­search re­port is avail­able on re­quest from FRT.