Fluorinated acrylic copolymers for repellency on suede leathers

6 February 2002

Suede leathers are usually not finished which makes them very sensitive to water and oil staining. In order to upgrade suede leathers and give them water and oil resistant properties without modifying their handle, they can be sprayed with aqueous solutions of fluorinated acrylic copolymers. The effect of adding crosslinkers to these solutions enhances the repellency performance of suede leathers. The leather's surface properties can be evaluated by using AATCC 118 (American National Standard) for the evaluation of oil resistance and a water-isopropyl alcohol (IPA) test concerning the evaluation of water repellency. This paper evaluates new fluorinated resins and crosslinkers. Experiments This study was meant to evaluate the improvement of surface properties of suede leathers when sprayed with different solutions of Foraperle 315, a fluorinated acrylic copolymer from Atofina. The sprayed suede leathers were processed without any additional Foraperle 315 in the drum. All the leathers studied were similar before the spraying process and were hand sprayed. Three parameters were studied: * Effect of Foraperle 315 by itself when sprayed on the surface of suede leather * Effect of a polyaziridine crosslinker when added along with a Foraperle 315 solution. We assume that the crosslinker should have a positive effect on the Foraperle 315 performance by crosslinking the fluorinated acrylic copolymer and allowing it to make a more continuous repellent film on the surface of the leather. Experiments were also carried out to study other availablecrosslinkers * Effect of temperature on the Foraperle 315 performance with and without a crosslinker. The crosslinking reactions are influenced by the temperature. In the tanneries, the spraying process is followed by an on-line drying process. Temperature during this drying process may allow some crosslinking reactions and may interfere with the surface properties of the leather. The effect of the temperature depends stronly on the chosen crosslinker. Procedure Two test methods were used to evaluate the surface properties of suede leather. Water-isopropyl alcohol (IPA) test The water repellency of treated samples is measured using a water-isopropyl alcohol test, and is expressed in terms of water repellency rating (0-10) of the treated leather. Treated leathers which are penetrated by or resistant only to a 100% water/0% mixture (the least penetrating of the test mixtures) are given a zero rating. Other intermediate values are determined by the use of other water-IPA mixtures, in which the percentage amounts of water and IPA are each multiples of 10. The water repellency rating corresponds with the most penetrating mixture that does not penetrate or wet the leather after 30 seconds contact. AATCC Standard Test 118 The oil repellency of leather samples is measured by AATCC 118, based on the resistance of treated leather to penetration of oils with varying surface tensions. Treated leathers resistant to Kaydol, a brand of mineral oil and the least penetrating of test oils, are given a rating of one, whereas treated leathers resistant to heptane (the most penetrating of the test oils) are given a value of eight. Other intermediate values are determined by the use of other pure oils or mixture of oils. The rated oil repellency corresponds to the most penetrating oil (or mixtures of oils) which does not penetrate or wet the leather after 30 seconds' contact. Higher numbers indicate better oil repellency. Considering the unevenness of the hand-spraying for each grade of each test method, two drops of the testing solution were deposited in three different places on each leather piece. In case of doubt, a fourth place was tested. Moreover, the penetration of the testing solution was sometimes difficult to observe even after removing the drop after 30 seconds (no stain on the flesh side, but only slow absorption of the drop). In this case, the penetration was evaluated through the presence of stains on the grain side (see Figure 1). Initial trials - Foraperle 315 Two solutions of Foraperle 315 were prepared: * 5% of F315 (95% of distilled water) sprayed (1g) * 5% of F315 and 1% of crosslinker, made up with distilled water For each solution, three pieces of suede leather were sprayed. Each one was maintained at different temperatures (ambient, 70°C and 85°C) for one minute (one minute is the usual drying time for leather in an auto-spray). Afterwards, the pieces were kept at room temperature. Crosslinker trials These trials evaluated the performance of the crosslinker with the Foraperle 315. Three solutions were prepared and sprayed. * 1% crosslinker (9048) made up with distilled water. This experiment was carried out to verify that the crosslinker had no water-repellent properties itself * 5% of an acrylic solution (RA 2394 from Stahl, medium soft acrylic, 35% solids content) which is not supposed to bring any water repellency properties alone * 5% of the same acrylic solution and 1% of the same crosslinker (9048) completed with distilled water Results See Table 1. Conclusion Effect of Foraperle 315 It was observed that Foraperle 315 brings some water and oil resistant properties to the suede leather (up to 3.5 for water resistance and 2.5 for oil resistance). This observation confirms the results we have previously obtained when using Foraperle 315 as a top coat for different finishing formulations. Foraperle 315 stays on the surface of the leather and acts as a good water and oil repellent. Effect of the temperature For these three sets of trials, no improvement was recorded when increasing the curing temperature. As for the trials with Foraperle 315 + crosslinker, this result can be explained because polyaziridine cures at a fast rate even at ambient temperature. The curing then does not bring any additional effect. Effect of the crosslinker The results show a drastic improvement of the surface properties of the suede leather when 1% of the polyaziridine derivative is added (from 3.5 to 7.5-8 for water repellency and from 2.5 to 5-6 for oil repellency). Other results show that the effect is due to crosslinking and not the crosslinker alone. The crosslinker helps the fluorinated resin to spread evenly and make a continuous repellent film. Impact of different crosslinkers Subsequent to the initial trials, the impact of different commercial crosslinkers used along with Foraperle 315 was studied on suede leathers. The aim was to check the efficiency of these different crosslinkers regarding water and oil repellency properties. All of the crosslinkers evaluated were chosen because of their crosslinking efficiency at room temperature. No curing temperature is required to activate the crosslinking reactions. See Table 2. The same suede leather was used to carry out the trials. All the leathers were hand sprayed and kept in the same conditions overnight. No drying process was used before testing. Results See Table 3. Conclusions By spraying a small amount of fluorinated resin, we can enhance drastically the repellency performance of the suede leather without adding any crosslinker. All the crosslinkers studied enhance the intrinsic properties of Foraperle 315, though the performance of the combination Foraperle 315 crosslinker varies. Astacin and Corial crosslinkers increase the water and oil repellency properties of Foraperle 315, but the enhancement is very slight (from two without crosslinker up to 2/3 as far as oil repellency is concerned). UA 9048 and Aqualen crosslinkers greatly enhance the properties of Foraperle 315. The Aqualen formulation shows better physical results than UA 9048 and the nap appearance of the suede itself is better. This appearance can be improved further by using a fine spraying in auto-spray. Conclusion Spray fluorinated treatments on suede leathers obviously bring very good oil and water repellency properties. By means of crosslinking a fluorinated acrylic copolymer, we have shown how to enhance the intrinsic efficiency of Foraperle 315. The appearance of leathers (nap) can be maintained by applying a fine spray coat of Foraperle 315 solution along with a crosslinker. The studies have shown that there is no visible disturbance of nap by using Aqualen along with Foraperle 315. Acknowledgement The authors thank the Central Leather Research Institute in Chennai, Elf Aquitaine and Atofina for cooperation and financial support. Authors: X François1, S Gupta2, S Sudhakar2, J Thierrée1, T Ramasami2, D Juhué1 1. Atofina, France 2. Central Leather Research Institute, Chennai, India

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