DEVELOPMENT OF WATERBORNE AND MILD CURING DWRS, FORMULATED WITH FULLY BIO-BASED SUBSTANCES

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INOM EXAMENSARBETE KEMITEKNIK, AVANCERAD NIVÅ, 30 HP , STOCKHOLM SVERIGE 2020

DEVELOPMENT OF

WATERBORNE AND MILD CURING

DWRS, FORMULATED WITH

FULLY BIO-BASED SUBSTANCES

JOHANNES R.S. VAN OVERMEEREN

KTH

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Abstract

Durable water repellents (DWR) are textile finishes that provide long-lasting water repelling proper-ties to functional garments. However, these hydrophobic finishes are commonly a source of polluting and persistent chemicals and are produced from fossil resources. As a result of increasing awareness, innovation towards environmentally friendly and biodegradable alternatives has progressed, yet no 100% renewable sourced products are available. In an attempt to create a bio-based, non-toxic DWR, that is curable under mild conditions, focus was put on the development of a shelf stable spray im-pregnation product intended for consumer use. By formulating dispersion/emulsion systems, a wide variety of commercially available, renewable sourced amphiphilic and hydrophobic molecules were evaluated on their effect on the water repelling performance of treated textile fabrics. Simultaneously, the produced systems were assessed carefully to create understanding on the effect of substances and their corresponding ratios on the stability. Promising candidate products that were selected for further investigation showed reasonable stability for 1 month at 40 °C, combined with an industrial standard spray rating of 3 (where 1 is the worst and 5 is the best) after 24 hours hang drying at room temperat-ure. On top of that, spray ratings of 5 could be reached after short time, non-industrial tumble drying at low temperatures, which could even be retained for at least ten laundering cycles on synthetic textiles. The selected finishes did not have a measurable effect on the breathability of the treated fabrics, while the majority did not considerably affect the hands-feeling or colour of the textiles. Be-sides several scaling up experiments and particle size measurements, extrapolation of the findings was carried out by testing the developed formulations on fifteen different types of textiles. Effects on appearance and feel were documented, additionally, contact angle, spray score, and wash durability were determined and compared with a commercially available product.

Keywords: Durable water repellents, Bio-based, Biodegradable, Emulsions, Fluorine-free, Functional

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Contents

1 Introduction 4

1.1 Trends, concerns, and opportunities in the fashion and textile industry . . . 4

1.2 Durable water repellents: From bad chemicals towards mimicking nature . . . 4

1.3 Application of DWRs concerns substrate, medium, and curing conditions . . . 6

1.4 Waterborne systems: Dispersions and Emulsions . . . 7

1.5 Bio-based and Biodegradable chemicals . . . 9

1.6 Aim and Strategy . . . 10

2 Materials 10 2.1 Formulation materials . . . 10

2.2 Textile fabrics . . . 10

3 Experimental 12 3.1 Preparation of DWR formulations . . . 12

3.2 Preparation of water repellent textile fabrics . . . 12

3.3 Microscopical determination of structural formulation appearance . . . 12

3.4 Determination of formulation particle size and distribution . . . 12

3.5 Determination of formulation stability . . . 13

3.6 Assessment of water repelling performance . . . 13

3.7 Laundering cycle simulation . . . 13

3.8 Contact angle determination . . . 13

3.9 Water vapour transmission rate . . . 13

4 Results and Discussion 14 4.1 Product stability . . . 14

4.2 Product particle size . . . 16

4.3 Breathability . . . 16

4.4 Water repelling performance - laundry durability . . . 17

4.5 Water repelling performance - textile types . . . 18

4.6 Property analysis of treated fabrics . . . 21

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1 Introduction

1.1 Trends, concerns, and opportunities in the fashion and textile industry

The shift towards more sustainable, environmentally friendly, and circular products is of high concern to all business areas. Not in the least place to the fashion industry which is responsible for an es-timated 6-8% of all global greenhouse gas (GHG) emissions.1,2 In line with the goals set in the Paris agreement (UNFCCC), the Fashion Industry Charter for Climate Action has committed to a 30% reduc-tion of GHG emissions in 2030.3Moreover, consumers around the globe are increasingly aware of the environmental impact of fashion, such that 75% consider sustainability extremely or very important when purchasing a fashion item.4,5 The environmental impact of fashion production can be broken down into the different life cycle stages, which provides a framework for targeted action (Figure 1).1

Fig. 1 Relative share of life cycle stage impact on environmental factors for the global fashion industry, adapted from Measuring Fashion report1

Strikingly, it can be seen that across all environmental parameters, the strongest contribution comes from the dying and finishing stage, which is therefore an important focus area in reaching the stated goals. However, it should be noted that long term sustainability of the fashion industry can only be achieved with reduction of (over)consumption, extension of product lifespan (slow-fashion), and novel circular business models.6

1.2 Durable water repellents: From bad chemicals towards mimicking nature

Certain functional textile finishing agents have attracted considerable negative attention because they are commonly a source of persistent organic pollutants (POPs). These are typically (poly)halogenated organic molecules, which have high environmental persistence and a strong bioaccumulation poten-tial.7A major class of POPs are per- and polyfluoroalkyl substances (PFASs) which are used in water (and stain) repellent finishes, because of their unique combination being both olephobic and hy-drophobic in character. Finishes containing these molecules are knowns as durable water repellents (DWR) because of their additional ability to survive multiple laundry wash cycles. Mechanisms for en-vironmental pollution from textiles, being treated with a DWR containing the PFAS perfluorooctanoic acid (PFOA) are discussed schemtically in Figure 2. Since 2019, PFOA is de facto banned under the Stockholm convention on POPs, but many other PFASs or other fluorine containing chemicals with slightly different structures (e.g., short-chain, branched) are still used widely and remain to be re-leased into the environment. Today, POPs and not in the least place PFASs are present in soil, fresh water, food, and therefore even in human tissue, hence of serious health concern.9_{In December 2019,}

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Fig. 2 Possible pathways through which PFASs used in textile finishes are released into the environment, PFOA derived structures are used as an example here, adapted from Holmquist and co-workers8

Thankfully, over the past years research in completely fluorine-free DWRs for outdoor, sports, and per-sonal protective garments has excelled and several concepts are successfully commercialised now.11,12

State-of-the-art DWRs containing more environmentally friendly water repellent techniques can gen-erally be subdivided in either silicone or hydrocarbon chemistries, but exact structural details are often trade secrets due to commercial interests. Silicone based DWRs generally show slightly lower durability than their hydrocarbon counterparts, whereas both types of chemistries do obviously not meet oil repelling properties of fluorinated DWRs.11 Nevertheless, competitive greener alternatives for water repelling finishes are widely available but still face some unexplainable resistance in the market.13 _{The single flaw of the new generation of DWR technologies is that although being clean}

and often biodegradable they still rely on fossil based resources. In the light of growing commercial interest for fossil free, bio-based, and carbon negative marketing strategies, a complete shift towards natural resources could prove to be the final step towards implementation of green DWRs. Nature has much longer provided structures that resist water based on surface roughness and hydrocarbon coatings.14 These have been an inspiration, but could be much more closely resembled if a future generation of DWRs would be completely derived from natural, renewable resources. Some of the most recent DWRs that are commercially available and suggest to be partially bio-based have been summarised in Table 1. Besides, most of these products claim readily biodegradability as well.

Table 1 Recent partially renewable sourced DWRs12,15

Manufacturer Product name Renewable Description

content

Beyond Surface Technologies miDori®evoPel 55% Certified Bio-based, Partially plant seed based Huntsman (Chemours) ZelanTMR3 63% Non-GMO partially plant sourced alkyl urethane OrganoClick OC-aquasilTM_Tex _unknown _{Plant-based catalyst with fatty polymers}

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1.3 Application of DWRs concerns substrate, medium, and curing conditions

Processes to apply DWR finishes to textile fabrics or garments can differ but require permanent de-position of hydrophobic moieties on the individual textile fibres. Textile fibres are long strains of crystalline polymers, that exhibit strength because of favourable strong secondary interactions (e.g., hydrogen bonding or π-stacking) or elasticity in block copolymers that contain both high and low Tg

segments. Molecular structure of common polymeric materials used in functional textiles are illus-trated in Figure 3. However, structural variations are possible, and many fabrics consist of tailored fibre blends to reach desirable properties. To provide some perspective on their relative use, the global annual production by volume of some of these fibres is show in Figure 4. In functional outdoor apparel, polyester (PES) and polyamide (PA) make up the vast majority of fibres used.

Since repelling finishes are applied in a final stage of the production process, the fibre surface is chemically complex containing dyestuffs and possibly other finishes. Hence, textile finishes are gen-erally anchored non-specifically on the fibre surface by taking advantage of the presence of functional groups. The usual method to apply a DWR is using an impregnation technique, in which the fabric is led through a (water-based) solution containing hydrophobic molecules, curing agent, and pos-sibly cross-linkers that increase durability.16_{Speed and concentration are controlled based on fabric}

characteristics such as: type, yarn thickness, and absorptivity.12Subsequently the fabric is then dried and cured at high temperatures, typically for a few minutes at temperatures exceeding 150 °C, which requires considerable energy consumption.11 Innovations changing the application procedure have been suggested in literature, for example iCVD plasma application17_{, as well as layer-by-layer}

meth-ods.18 These novel techniques often aim for reduced consumption of chemicals or energy, but are less applicable on industrial production scale or require fundamental changes to production lines. In addition, spraying techniques are used industrially for delicate technical textiles as well as in con-sumer aftercare products. The latter type of product is intended to provide customers the ability to (re)finish garments with a DWR that is fully curable under non-industrial conditions. Clearly, this poses a technological challenge, since the product should be curable by either hang-drying or in a non-industrial tumble drier. Furthermore, the amount and concentration can not be controlled and the product should ideally be compatible with different types of garments, irrespective of their prior treatment. Ultimately, the product requires high shelf-stability because of potential long retention times in retail and on customer shelf under variable and uncontrolled storage conditions.

Fig. 3 Molecular structures of repeating units in textile fibre polymers used for the production of functional fabrics

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1.4 Waterborne systems: Dispersions and Emulsions

Water-based solutions used for DWR application are usually two-phase systems, in which the hy-drophobic material is dispersed in a (hydrophilic) water phase. Two-phase systems are kinetically unstable, and have a tendency to separate. To prevent this, the hydrophobic molecules are coated in a shell of amphiphilic molecules, which have chemical structures with both a hydrophobic and hydrophilic part. These amphiphilic molecules are also known as surfactants, because they stabilise a dispersed system by decreasing the surface tension between the two phases in such a way that they are ordered on the oil-in-water (O/W) interphase. In order to minimise the surface to volume ratio, the dispersed phase is present as spherical droplets or particles.

Particles are schematically depicted in Figure 5, together with three main governing factors determ-ining the stability of the dispersed system. Surface charge can be facilitated by surfactants contadeterm-ining charged groups (e.g., in soaps and detergents). Thus, either cations or anions present on the in-terphase create a protective shell that induces a repelling effect between the different particles. When the surface charge is insufficient to keep particles from reaching each other, instability can be observed by aggregation or coagulation, and coalescence can be a result (see Figure 6). Partial coalescence is a type of coalescence observed in systems with solids in the dispersed phase, in which no complete co-alescence of two globules takes place, due to fixating behaviour the internal (semi)crystalline particle structure. This mechanism can also be induced as a result of uncontrolled crystal growth piercing through the amphiphilic shell of the particles, accelerated by mechanical shear crystals meet and de-velop a (semi)crystalline network of interlinked partially coalesced particles19,20_{. Related to surface}

charge is the surface chemistry of the hydrophilic heads. In fact, not all surfactants bear charge and these are known as non-ionic surfactants. Depending on the type and amount of functional groups present, interactions with the water phase can vary. Effective surfactants contain structures that can participate in the hydrogen bonding network present in the water phase, however large hydrophilic regions create water solubility, which might induce destabilising migration of surfactants from the particle surface. Moreover, water soluble surfactants might migrate to the water-air surface, where they can lead to undesirable formation of foams.

Fig. 5 Factors influencing particle sta-bility, adapted from Estabrook and co-workers21

Fig. 6 Different instability mechanisms that can be observed in emulsion and dispersion systems, adapted from Fredrick and co-workers20_{, reverse}

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A heterogeneous particle size distribution might be the reason for observing Ostwald ripening. This type of instability is driven by a difference in internal surface tension between particles. The surface tension in a small droplet is higher than in a large droplet, which drives absorption of the small droplet by the large droplet. Because this leads to an over time increase of the size of particles, creaming or sedimentation can be a result. Creaming or sedimentation (see Figure 6) happens when there is a discrepancy between the densities of the two phases, so that the dispersed phase either sinks or floats. However, with reducing particle diameter these effects are slowed down drastically, creating practical stability. Natural movement of dispersed particles or droplets called Brownian motion is the reason that strong directional separation of phases is prevented. Therefore, particle size is an important element influencing the steadiness of a dispersed system. In addition, smaller particles size allows for higher concentrations of dispersed material in the water phase, compare to the difference between a bucket of melons or peas.

In so-called nanoemulsions or nanodispersions, several aspects play a role in obtaining a homogen-eous small particle size (typically below 0.5 µm). Most importantly, a relatively large share of am-phiphilic material is needed, because decreasing particle size increases the total surface area. This is partially driven by the presence of charged surfactants, as charge does not only repel other particles, but also charges within one particle, increasing the total surface area of the system. However, particle size is dependent on the wetting angle of surfactants as well. This means that the size of the hy-drophilic heads influences the curvature on the surface, larger hyhy-drophilic groups allow for greater curvature which is necessary for small particles. Besides, co-solvents (small surface active molecules) can be used to ‘fill up the gaps’ on the interphase. Above all, energy is required to disperse the im-miscible phases within each other, which can be facilitated using proven methods such as high-shear mixing, ultrasonication, and high pressure homogenisation, among others.

In the case of DWR systems particle size can also influence the amount of hydrophobic material applied on the surface, an simplified representation of DWR deposition on a textile fibre is shown in Figure 7. Small globules allow for nano-scale deposition, which creates favourable surface roughness, boosting the water repelling effect.22 Besides, certain surfactant molecules can also affect repelling properties negatively, when they act like re-wetting agents. In that case hydrophilic heads are exposed on the hydrophobic surface, which causes absorption of water on the fabric surface. Surfactants with relatively large hydrophilic groups are more prone to causing this deteriorating effect, which are therefore less applicable in DWR formulations.

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1.5 Bio-based and Biodegradable chemicals

Bio-based chemicals are structures derived from vegetable or animal based resources. A distinction can be made between bio-derived or fully bio-based chemicals, of which the first is partially derived from vegetable feedstock and the latter entirely. Determination of the bio-based content of chemicals is based on the amount of biocarbon present in its structure. This share of renewable carbon can be measured using an isotope comparison method that is similar to techniques used for carbon dating. Carbon-14 presence is only observed in products from renewable resources, hence a marker for the amount of bio-derived material. End-products formulated from bio-based resources can be marketed and labelled as bio-based, for example using the Austrian TÜV label or USDA Bio-preferred label, which differentiate products based on their percentage of bio-based content.

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1.6 Aim and Strategy

Considering both the technical and commercial possibility as well as the environmental necessity, the following thesis was stated: A bio-based, biodegradable, and non-toxic DWR for household use can be formulated as a stable O/W emulsion/dispersion system. To progress towards this goal, a set of trial emulsions and dispersions were formulated selecting from a broad range of bio-based commercially available amphiphilic and hydrophobic molecules. Firstly a combination of amphiphilic molecules was optimised, while keeping a fixed hydrophobic phase. The formulations were evaluated on their (shelf-) stability, producibility, appearance, environmental profile, and water repelling performance on two reference textiles. By formulating in series, new insights could be evaluated continuously, which allowed for fast feedback loops and minimal use of raw materials. In the following stage, combinations of bio-based hydrophobic molecules were altered, adding softness, time to see effect, and cost to the quality parameters as used in the first stage. If necessary, the amphiphilic phase was then again adapted to improve shelf-stability based on accumulated knowledge. In total 130 formulations were prepared and named using an ordinal system (JO-10xx or JO-11xx). Repetition in larger size batches received corresponding codes in the format: JO-14xx. Candidate selection for more in depth study took place based on indicative stability, performance on textiles, and difference in chemical nature. Two main candidates JO-1172 and JO-1195 were selected for all studies, in combination with another one to seven formulations for comparison depending on the type of study. From these selected candidate systems, more information was gathered on particle size, accelerated shelf life, as well as their scalability. The latter was carried out by changing processing parameters, evaluating addition sequence, and increasing the concentration of solids. In addition, the laundering durability of the candidate DWR’s and their effect on fabric breathability were assessed for reference textiles. Finally, candidate formulations were evaluated on their performance, appearance, softness, and durability on a wide set of textile types, including laminated fabrics and fibre blends.

2 Materials

2.1 Formulation materials

Substances included in this study were selected based on their amphiphilic and hydrophobic charac-teristics. In addition, they had to be commercially available while being completely bio-based (100% renewable carbon), extra attention was put towards chemicals classified as inherently biodegradable or food contact safe materials. In rare cases, non bio-based products were used as structures for comparison purposes, or when they were known to be available from renewable resources as well. Moreover, safety data sheets (SDS) as well as technical data sheets (TDS) were analysed thoroughly to predict the functionality of the substances of interest. Using information on specific biodegradability of individual ingredients, overall biodegradability of formulations was theoretically estimated. Water used in formulations was deionised using a PURELAB Prima DV 35 water purification system (ELGA, Celle, DE).

2.2 Textile fabrics

In the study several different textile fabrics were used, which are summarised in Table 2. The two textiles printed in bold were used as reference textiles and used for the majority of the experiments. Fabrics were cut in roughly square pieces with dimensions between 0.05 m2_{to 0.1 m}2_{. Thickness was}

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Table 2 Overview of textiles used in the study

Description Colour Hand Weave Primary Ratio Secondary Ratio Thickness Grammage

materiala _(%) _materiala _(%) _(mm) _(g/m2₎

Ultralight square patterned polyamide Navy Blue Smooth & soft Plain PA 100 0.1 57

Light shiny polyamide Bone Smooth & soft Plain PA 100 0.2 105

Soft nylon with wicking Hytrel®laminate Medium Blue Soft & stretchy Plain PA TPC-ET 0.2 103

Stretchy polyamide elastane blend Black Textured & stretchy Twill PA EA 0.5 262

Hardwearing polyamide cotton blend Steel grey Textured & sturdy Plain PA 69 CO 31 0.4 259

Thick sturdy strong cotton blend Ebony Rough & sturdy Plain CO 70 PA 30 0.5 328

Thick strong soft canvas Black Textured & soft Plain CO 60 PES 40 0.5 340

Cotton warp & stretchy weft denim Denim Rough & sturdy Twill CO 77 PES/EA 22/1.5 0.6 359

Soft thick two-layer fleece Moss Green Soft & uneven Knit CO 60 PES 40 0.9 277

Soft stretchy fleece Black Soft & stretchy Knit PES 88 EA 12 1.0 201

Thin light smooth polyester White Smooth & soft Plain PES 100 0.17 120

Directionally woven thin polyester Amber Textured & sturdy Rib PES 100 0.25 127

Thin textured polyester Medium Blue Textured & soft Twill PES 100 0.4 199

Thick textured cotton viscose blend Black Textured & soft Plain CO 62 VI 38 0.6 355

Thick soft strong merino wool Black Textured & soft Plain WE 100 1.0 364

a_{: EA = elastane CO = cotton, PA = polyamide, PES = polyester, TPC-ET = thermoplastic copolymer elastomer, VI = viscose, WE = Merino wool}

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3 Experimental

3.1 Preparation of DWR formulations

Both hydrophobic and amphiphilic constituents were mixed in a beaker glass in ratios according to the suggested recipe. Deionised water was boiled using a kettle and after measuring directly added to the mixture, resulting in complete melting of the ingredients. The 200 g mixtures were subjected to a homogenisation cycle using a Polytron 1300D (Kinematica AG, Luzern, CH). Starting with 1 min at 10,000 rpm, the speed was gradually increased to 17,000 rpm. The temperature was measured and when between 50 °C to 60 °C, catalyst was added to the mixture. After 9 min homogenisation was stopped and a coarse dispersion/emulsion obtained. Part of the coarse mixture was left to cool down under ambient conditions, while the other part was subjected to an additional 4 min ultrasonication step. The sonication probe (MSE, Heathfield, UK) was operated at a frequency between 20 kHz to 24 kHzand amplitude of 10 µm. If considered successfully emulsified based on their appearance under a microscope (section 3.3), samples were stored under ambient conditions in 250 mL PET containers. Formulation preparation was adjusted for certain samples to facilitate faster cooling, utilising con-centrated homogenisation and sonication, followed by a late dilution step with cold water. In this method, all ingredients were heated until molten on a heating plate, and after addition of 60 mL to 80 mLdeionised water (90 °C) mixed using a laboratory homogeniser at 10,000 rpm. Rotation speed was increased gradually to 20,000 rpm after addition of the catalyst. Homogenisation was carried out for 6 min at 75 °C to 90 °C, followed by sonication for 4 min to 6 min. The obtained emulsion was subsequently cooled down quickly by addition of 300 mL deionised water (<20 °C). Hereafter, more catalyst was added to the emulsion. Qualitative observations in time were carried out by visual as-sessment of particle deposition, apparent viscosity, smell, and colour. Variations on this latter method were made to assess upscaling possibilities, by altering the concentration of dispersed material, as well as the amount and addition point of catalyst.

3.2 Preparation of water repellent textile fabrics

Formulations prepared as described in section 3.1 were diluted to their effective concentration with deionised water. Pieces of fabric were completely sprayed using a common tunable spray head. After 2 min this procedure was repeated once to ensure full saturation of the textile, excess product was wiped off using a paper towel. Treated textiles were left to hang dry at ambient conditions overnight. After determination of the spray score as described in section 3.6, textiles were dried in a tumble dryer (Electrolux T5130 LAB, Stockholm, SE) at 58 °C for 30 min, followed by a 5 min cooling step. Fabrics were stored in a climate room set to 23 °C and 50% relative humidity (RH).

3.3 Microscopical determination of structural formulation appearance

Prepared systems were structurally analysed under an optical microscope (Nikon Microphot FXA, Tokyo, JP). One undiluted droplet of material was used for visual assessment using a 10x PlanApo objective. Pictures were captured using a mobile phone camera (f/1.7, Motorola, Chicago, IL, USA).

3.4 Determination of formulation particle size and distribution

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3.5 Determination of formulation stability

All formulations prepared in accordance with section 3.1 stored under ambient conditions were mon-itored on their stability after 24 hours. Selected formulations were added to plastic centrifuge tubes (15 mL) and stored at 4 °C, 40 °C, and 50 °C using a regular fridge and heated storage chambers. For-mulation quality was analysed after 9, 15, 24, and 31 days and photographically documented. In addition, products were analysed and evaluated according to the method described in section 3.3. Moreover, viscosity difference over the course of one month was determined for the samples stored at 50 °C. Before and after heated ageing, the viscosity was measured at 200 rpm using a Brookfield DV-II+ Pro rheometer (AMTEK Brookfield, Middleboro, MA, USA), equipped with a SC4-18 spindle.

3.6 Assessment of water repelling performance

Using a standardised device complying to ISO 4920:2012 standards23, spray scores were assessed on a photographic scale. Tests were performed by spraying 250 mL deionised water under a 45° angle on the textile fabric. Prior to testing samples were conditioned for at least 30 min in a climate chamber set at 23 °C and 50% RH.

3.7 Laundering cycle simulation

Selected treated fabrics were exposed to laundering cycles in mesh laundry bags using a Wascator FOM71 CLS (Electrolux, Stockholm, SE) equipped with cotton ballast. The used programme operated at a temperature of 40 °C and used standard non-phosphate detergent (1.25 g L−1). Subsequently, fabrics were tumble dried after completion of every wash cycle according to the procedure described in section 3.2. To avoid cross-contamination between textile fabrics treated with different chemistries, reference products and study trials were washed separately. Performance testing was carried out after 1, 5, 10, and 15 washes according to the procedure described in section 3.6. For selected reference textiles, fabrics were resprayed with the same product and tumble dried after the Spray score dropped to 3.

3.8 Contact angle determination

Static contact angles were measured using a PGX portable goniometer (Messmer-Büchel, NL). Drops of 6 µL deionised water were used and pictures were taken using an integrated camera. The sys-tem was calibrated half an hour after set-up to ensure equilibrium conditions. Contact angles were determined quantitatively by automatic processing using PGX software, after manual tuning of the baseline. Prior to testing samples were conditioned for at least 30 min in a climate chamber set at 23°C and 50% RH.

3.9 Water vapour transmission rate

Water vapour transmission rate (WVTR) was determined using a variation on the upright cup method as described in ASTM E 96, Procedure B, Standard Test Methods for Water Vapor Transmission of Materials.24,25_{. 250 mL PET containers were filled with 210 mL deionised water, which ensured less}

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4 Results and Discussion

4.1 Product stability

The two-phase systems were formulated aiming for long-term kinetic stability, an essential require-ment for the intended application. Observed instabilities included phase separation, phase inversion, gelling, flocculation, and partial coalescence, which could often be observed directly after production (Section 3.3). In certain instances homogenisation yielded an unstable product, yet reasonable kin-etic stability was obtained after the sonication step. Phase inversion, gelling, and partial coalescence were often shear catalysed and happened during or after cooling. Gelling was often accompanied by increased foam formation. Kinetically stable appearing candidate products were subjected to a longer stability study carried out at different temperatures (Section 3.5). Heated ageing is a tool to predict stability over longer times at room temperature in which stability for 4 months at 40 °C or 1 month at 50°C roughly corresponds to 1 year stability at room temperature. The stored formulations showed similar stability behaviour, and results for two of the products are depicted in Figure 8 and Figure 9.

Fig. 8 Observed stability at different temperatures and incubation times for product JO-1172

Fig. 9 Observed stability at different temperatures and incubation times for product JO-1195

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Fig. 10 Microscopic images of JO-1172, a). Appearance directly after production b). Storage for two weeks at 40°C c). Storage for two weeks at 50°C d). 1 month at room temperature e). 1 month storage at 40 °C f). 1 month storage at 50 °C

Fig. 11 Microscopic images of JO-1195, a). Appearance directly after production b). Storage for two weeks at 40°C c). Storage for two weeks at 50°C d). 1 month at room temperature). 1 month storage at 40 °C f). 1 month storage at 50 °C

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4.2 Product particle size

Laser particle size analysis was carried out to quantitatively map the particle size and distribution of three different candidate products, which are compared with a reference product in Figure 12.

Fig. 12 Particle size for analysed candidate products and reference

Fig. 13 Microscopic images for products subjected to particle size analysis, order corresponds with the legend in Figure 3.4

The reference sample has a particle size below 0.5 µm, ensuring sufficient stability. On the other hand, the graphs for the tested candidate products show an irregular distribution and presence of extremely large particles which are not observed under the microscope (see Figure 13). During the preparation procedure for particle size analysis, high dilution and increased shear stress from vigorous stirring likely accelerated instability processes leading to formation of larger aggregates. The peaks in the smaller regions show similar particle sizes compared to the reference product, in particular product JO-1195 falls within the range of the reference. JO-1495 is a scaled up copy of JO-1195 and shows a wider size distribution, which could be explained by loss of processing efficiency due to large scale processing with limited laboratory equipment. The same is true for JO-1472, being a scaled up version of the non analysed JO-1172 sample, included in the ageing study. However, it is apparent from Figure 13 that the particle size for the candidate products is higher than for the reference product. This suggests that the main portion of particles prone to aggregation instability are in the larger size range, measuring several micrometres. Longer sonication times or higher energy equipment, as well as increased surface charge are parameters that can decrease the particle size of candidate products even further.

4.3 Breathability

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0.0 10.0 20.0 30.0 40.0

JO-1172 JO-1177 JO-1181 JO-1195

W at er v ap ou r t ra ns m is si on ra te (g h -1m 2)

Ambient hang dry Tumble dry Untreated fabric Fig. 14 WVTR for candidate products on blue polyamide

0.0 10.0 20.0 30.0 40.0

JO-1172 JO-1177 JO-1181 JO-1195

W at er v ap ou r t ra ns m iss io n ra te (g h -1m 2)

Ambient hang dry Tumble dry Untreated fabric Fig. 15 WVTR for candidate products on white polyester

4.4 Water repelling performance - laundry durability

Products intended for use as DWR require high durability during repeated laundering cycles (Section 4.5). This attribute was assessed on two synthetic textiles. Seven different candidate products were included to obtain insight in the influence of product composition on DWR retention. In Figures 16 and 17 it can be seen that all products show a similar durability, regardless of the difference in composition. The effect of the textile type seems to be more apparent, since the material is retained longer on polyester, than on polyamide. While scores drop after ten wash cycles for the thin polyamide fabric, the treated polyester fabric shows extremely high durability even after twenty-five cycles.

1 2 3 4 5

Tumble dry First wash Five washes Ten washes Fifteen

washes tumble dryRespray

IS O 4 92 0 Sp ra y ra tin g JO-1032 JO-1108 JO-1136 JO-1172 JO-1177 JO-1181 JO-1195

Fig. 16 Durability performance of treated polyamide

1 2 3 4 5

Tumble dry First wash Five washes Ten washes Fifteen

washes Twentywashes Twentyfivewashes

IS O 4 92 0 Sp ra y ra tin g JO-1032 JO-1108 JO-1136 JO-1172 JO-1177 JO-1181 JO-1195

Fig. 17 Durability performance of treated polyester

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4.5 Water repelling performance - textile types

The performance of five candidate products with different compositions were assessed on fifteen different textile types as described in Table 2. In Figures 18, 19, 20, and 21 performance on four different types of polyamide are shown. Although the reference product shows generally a slightly higher score after ambient drying, all candidate formulations outperform the reference product after tumble dry curing, as well as on durability. Some of the graphs show a higher score after washing or repeated washing, this could be due to analysis of different parts of the textile, while local defects were being observed earlier. Besides, detergent molecules or re-wetting ingredients could have lead to a lower score, which were then sufficiently removed in a repeated laundry cycle. No negative effect on performance was found when the tested fabric contained elastane or when it was laminated with a hydrophilic membrane. 1 2 3 4 5

Untreated Overnight dry Tumble dry First wash Five washes

IS O 4 92 0 Sp ra y ra tin g Fossil C Ref JO-1404 JO-1418 JO-1472 JO-1495

Fig. 18 Water repellency on ultrathin blue polyamide

1 2 3 4 5

Fig. 19 Water repellency on shiny grey polyamide

1 2 3 4 5

Fig. 20 Water repellency on black polyamide elastane blend 1 2 3 4 5

Fig. 21 Water repellency on blue supplex nylon with wick-ing laminate

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1 2 3 4 5

Fig. 22 Water repellency on thin white polyester

1 2 3 4 5

Fig. 23 Water repellency on directional amber polyester

1 2 3 4 5

Fig. 24 Water repellency on blue textured polyester

Many performance textiles are blends of fibres, combining strength and comfort. In Figures 27 and 29 performance of the DWRS on strong polyamide reinforced polyamide/cotton blends are shown. A trend similar to the score on the cotton/viscose fabric could be observed here, where initial scores were high suggesting successful absorption of the DWR material, but low laundry durability with loss around folding lines. The black textile containing more cotton (60%) shows a faster reduction in repelling effect compared to the steel grey fabric which consist of only 31% cotton. All products, as well as the reference product showed a low water repelling effect on the denim fabric shown in Figure 28. This could probably be due to dyestuffs or washing agents used on the fabric, hindering efficient deposition. Again a cotton rich fabric showed lower durability, compared to pure polyester fabrics, even losing proofing after the first laundry cycle for all products. This observation aligns with the data for the thick sturdy cotton polyester fabric given in Figure 30. Spray scores show a steep drop after washing, although the fabric was initially waterproof, also here a loss of proofing was observed after 5 washes. In order to reach high durability on cotton containing textile blends, different strategies

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Fig. 25 Water repellency on thick black cellulose blend

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Fig. 27 Water repellency on black PA reinforced cotton polyester blend 1 2 3 4 5

Fig. 28 Water repellency on thick cotton polyester blue washed denim 1 2 3 4 5

Fig. 29 Water repellency on grey PA reinforced PA cotton blend 1 2 3 4 5

Fig. 30 Water repellency on thick ebony polyamide cotton blend

need to be employed to reach the durability as observed for synthetic textiles. These should be aiming on the formation of stronger chemical bonds between the hydrophobic material and cellulose. Fleece is a class of fabrics that is valued for it’s insulating properties, however the hairy structure makes it hard to treat with finishes. In Figures 31 and 32 the performance of the DWR finishes on two different types of fleece is shown. Relatively high scores were obtained for later formulations JO-1472 and JO-1495 on the synthetic fleece made from knitted polyester, but surprisingly these were not as durable as their woven counterparts. This could be due to the fact that high amounts of product were absorbed in the fleece, which allowed for ineffective orientation. Other formulations were not as effective, but outperformed the reference product. The green cotton fleece made up from cotton and polyester showed a curve similar to the denim, which suggested not very effective absorption of the DWR products, however it did remain proof after the first laundering cycle.

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Fig. 31 Water repellency on black fleece (polyester elastane blend) 1 2 3 4 5

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4.6 Property analysis of treated fabrics

Finally, the visual and tactile appearance of delicate textile fabrics should not be altered by the finish it is treated with. Therefore, treated fabrics were tested on stiffness, softness, colour change, and susceptibility to abrasion marks. In Figure 33 stiffness of the treated fabrics was evaluated by ex-amining their bending behaviour. Although many different fabrics were tested, general trends could be observed which were in line with the observations from the polyester fabric shown. Most hang dried fabrics showed a stiffness comparable to the untreated textile, which changed after tumble dry-ing. Especially JO-1004, JO-1118 and JO-1172 lead to considerable stiffening of the textile fabrics, where JO-1004 also induced had a roughening effect on the hands-feeling. The reference product induced a softening effect, while a neutral effect was obtained for product JO-1195, showing only slight stiffening of the fabric. Abrasion marks were not clearly observed on most textiles, but could be distinguished on some of which one is shown in Figure 34. The reference product only showed abrasion marking after tumble drying, where the candidate products all facilitated marking with a nail scratch. Treatments with formulations JO-1118 and JO-1195 showed less susceptibility to this negative quality attribute compared to JO-1004 and JO-1172.

Fig. 33 Observed stiffness of treated and untreated poly-ester textile after 24 hours hang drying (a) and after tumble drying (b)

Fig. 34 Observed abrasion marks on a treated polyester textile after 24 hours hang drying (a) and after tumble drying (b)

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5 Conclusions and Outlook

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