With proper design of the waveguides and supporting equipment, a specific environment (at the particular wavelength) can be created in order to provide controlled distribution of the microwave energy, making it possible to achieve uniform exposure to material passed through a channel. The leakage of microwave energy is inherently small due to the fact that waveguide slots are oriented along the wave guideline of symmetry, and therefore they cannot act as efficient slot antennas. Furthermore, in this way the material lies in the maximum of the electric field that assures effective coupling to the flowing microwave energy. In a case that request for slots symmetry is fulfilled, only the load (textile material) which passes through the waveguides has an influence on energy loss. The amount of microwave energy absorbed by the textile in each waveguide pass depends on the material thickness and moisture content.

In a case of single pass applicator, exponential decay of electric field might cause non-uniform heat distribution. To prevent this negative tendency, the material is passed through a number of waveguide passes. Additionally, the level of applied microwave energy is increased by the use of second magnetron, that feeds the applicator at the other end. Meander type of traveling wave applicators provides uniform energy distribution across the treated material.

Before this novel device comes into commercial use, the unintentional leakage of microwave energy must be checked in order to comply with existing safety regulations of Ministry [12]. The upper limit of tolerable microwave irradiation for professional exposure is 10 W/m², or 1 W/m² in higher sensibility range. Preliminary determination of irradiation level has been performed at Department of Radio communications and Microwave Engineering at Faculty of Electrical Engineering and Computing.

Applied material and chemicals

Pre-treated cellulose fabrics, 100% cotton (desized, scoured, bleached and mercerised) of different surface mass: 105 and 250 g/m² were used in the study. The fabric samples were passed through squezze rolls on laboratory foulard, Benz, Zrih Switzerland to give wet pick up of 100% owf. Impregnation was performed with baths containing reagents for durable press finishing (baths 1-4), water and oil repellent finishing (bath 5) and flame retardant finishing (baths 6-7), shown in Table 1. After the impregnations part of the samples was dryed by conventional method in a tenter at 110 C for 2 minutes and cured in a second pasage under the producer instructions. Second part of the samples was treated by microwaves in planar microwave device with the speed of 0,5 m/min.

2.2.1. Durable Press (DP) Finishing

N-methylole based reagents, such as dimethyloldihydroxyethylene urea (DMDHEU), as well as newly developed polycarboxylic acids (PCA) represented with 1,2,3,4-butanetetracarboxylic acid (BTCA) were used in the study [13-15].

Applayed baths were containing:

DMDHEU as conventional agent with high formaldehyde (HF) content

etherified DMDHEU with low (LF) formaldehyde content

dymethylglyoxalurea (DMGU) as non-formaldehyde or free formaldehyde (FF) agent

BTCA as FF agent applied with sodium hypophosphite (SHP) catalyst.

Effects of Durable Press finishing were determined as wrinkle recovery angle (WRA) according to ISO 2313 method and tensile strength according to DIN EN ISO 1394-1. Free formaldehyde was determined by AATCC 112 method. Whiteness degree was measured at reflective spectrophotometer Datacolor - Spectraflash SF 300 at D 65/10 conditions with Data Match 300 program according to AATCC 110-2000 method.