Cotton and Polyester Fabrics Plasma Coated with Hydrogenated

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cation. Whether a liquid is repelled or absorbed depends on the chemical composition

and the morphology of the surface [35]. Previous studies determined that oxygen plasma

pretreatment is more effective than argon and hydrogen for the super-hydrophilic/ultra-

hydrophobic properties for a-C:H film layers [27]. The textile structure and construction

depend on the type of weave patter, g/m² of fabric, type of the fiber content, fiber fineness,

and also the yarn parameters like the twist factors [36]. Textile materials consequently have

a complex surface composed of the inter-fiber/filament space, inter-yarn space and the pore

size distribution. Therefore, plasma treatment of textile fabrics is more challenging than for

solid polymeric materials [37, 38].

The present study investigates a-C:H films (30 and 60 nm thick) on cotton, polyethy-

lene terephthalate (PET), and cotton-PET mixture (COT/PET, 50:50) fabrics that serve as

intermediate layer for subsequent impregnation with immortelle oil and water glass. Be-

fore the textile substrates are coated via PECVD using acetylene (C2H2) an oxygen (O2)

plasma was previously applied for cleaning and activation. Overall the three textile types

as pure, oxygen treated and coated with two a-C:H coatings are individually refined or

combined with immortelle oil (IO) and water glass (WG) in preparation for enhanced re-

pellency properties to suppress mosquito attacks that cause vector-borne diseases.

15.2

COATING PROCESS AND ANALYTICS

The used PECVD vacuum system is sized 600 x 600 x 750 mm and suitable for coating

sensitive samples as the temperature does not exceed 40°C [16 - 18]. The fabric samples

cotton, PET and COT/PET were cut into pieces of 210 x 279 mm. Each fabric sample is

fixed along short edge top and bottom between two full-length aluminum poster clamps.

To avoid swinging, the bottom clip is extra weighted. The as prepared fabric samples are

mounted with the top clip in the chamber freely hanging on rotating rods, which in turn are

mounted on a rotating plate. This planetary-like system is operated with 2 rpm to ensure

uniform coating. The deposition process is described in detail in [16]. In brief: Exposition

to plasma is conducted at 10^-3 Pa with firstly O2 (10 min, 1 Pa, 200 W) and subsequently

with C2H2 (15 and 30 min, 0.65 Pa, 107 W, deposition rate 2 nm/min). This has proven to

be very efficient for textile fabric treatments, because the mean free path in the gas phase

is higher, so that gas-textile collisions are favored over gas-gas collisions [36]. The a-C:H

coated fabrics are treated afterwards using a pad-dry-cure procedure (Benz pad-dry sys-

tem, Germany), impregnated with a finishing bath containing 10 g/L WG and/or 5 g/L IO,

squeezed, dried at 110°C for 2 min, and finally cured 4 min at 150°C [39].

The morphology of the a-C:H coated textiles were investigated by scanning electron

microscopy (SEM, Philips SEM515), especially to check the quality of plasma treatments

on the fibers. The air permeability was evaluated with a SDL ATLAS M021S in standard

atmosphere. According to ISO 9237:1995 the rate of air flow which passes perpendicularly

through a test surface area of 5 cm² under an air pressure drop of 100 Pa was measured

[40]. The test was repeated at different locations on the sample at least five times and aver-

aged. The tensile properties of the fabrics were performed according to ISO 13934-1:2013

for the determination of maximum force using a strip method strength tester/tensiometer