Oxidative unhairing with hydrogen peroxide: development of an industrial scale process for high-quality upper leather

Transcription

1 Oxidative unhairing with hydrogen peroxide: development of an industrial scale process for high-quality upper leather Simona Bronco (1) Domenico Castiello (2) Gabriele D Elia (3) Maurizio Salvadori (2) Maurizia Seggiani (3) Sandra Vitolo (3)* (1) Istituto Nazionale per la Fisica della Materia, Dipartimento di Chimica e Chimica Industriale Università di Pisa, Via Risorgimento, Pisa, Italy (2) Po.Te.Co. Scrl - Polo Tecnologico Conciario Via W. Tobagi, Castelfranco di Sotto Pisa, Italy (3) Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali Università di Pisa, Via Diotisalvi, Pisa, Italy Tel , Fax , vitolo@ing.unipi.it * corresponding author 1

2 Abstract As an alternative to the traditional process based on the use of sulfides, an unhairing process in drum by hydrogen peroxide was developed for the production of high-quality bovine upper leather. A preliminary investigation at laboratory scale has allowed us to set out the optimal process conditions, in terms of H 2 O 2 dosage and ph, in order to achieve an effective unhairing and a compatible swelling of the hide. The pilot and industrial scale runs have assessed the industrial feasibility of the process that allows the production of a versatile base for different final applications of the leather (either chrome or vegetable tanned), and appear practical to implement as well as compatible with the existing machinery. The finished leather obtained by the innovative unhairing process shows good physical-mechanical and technical properties comparable with those of the traditional process, and the leather was technically assessed as satisfactory and suitable for use in the production of high quality upper leathers. The major pollutants of the oxidative unhairing, either as absolute concentrations or if normalized with respect to the salted weight processed, appear quite similar to the traditional process. The evident advantage is obviously the complete absence of dissolved sulfides in the exhaust baths of the oxidative process. Scanning electron microscopy was used as investigation method to better understand the mechanism of the oxidative unhairing in comparison with the traditional. 2

3 Introduction The ever increasing attention to the environmental impact of the process industry imposes an obligation to constantly improve the global sustainability of the tanning process. It has become thus necessary to minimize the pollutant charge of the effluents and the production of wastes. Among the numerous phases of the tanning process, the beamhouse phase represents 83% of the BOD5, 73% of the COD, 60% of the suspended solids, 68% of the salinity and 76% of the total polluting charge produced during the manufacturing process of hides 1. Besides, in the beamhouse, the traditional unhairing process with sodium sulfide and lime is responsible for most pollution. Consequently, the development of an alternative unhairing process, characterized by a lower environmental impact than the traditional, represents a priority in the leather research field. Prerequisites of any alternative unhairing process are that it must impart to the treated hides at least equivalent properties to those of the traditional, allow the production of a versatile basis for different types of finished product, and the process must be practical, economical to implement as well as compatible with the existing machinery. Among the numerous studies undertaken to develop unhairing processes alternative to the traditional 2-9, the unhairing of hides by oxidation is revealing interesting perspectives The use of oxidizing agents, such as calcium peroxide 13 or hydrogen peroxide 14 has been recently proposed for a rapid unhairing by spray application in enclosed chambers. This procedure, that can be applied on an animal s carcass, may represent an alternative to conventional unhairing in drum. In this work, the use of hydrogen peroxide for unhairing in drum, as an alternative to the traditional unhairing by sulfides, was investigated. The investigations of Shi et al. 12 about the mechanisms of hair removal from hide and the influences of hydrogen peroxide on the pelt in a highly alkaline medium were taken as the basis to develop a process industrially feasible. By preliminary study at laboratory scale, the optimal process conditions in terms of hydrogen peroxide offer, ph, drumming times were assessed. The process was successively validated on pilot scale where the oxidative unhaired skins were submitted to a traditional chrome tannage and dyeing/fatliquoring. The main physical and mechanical properties, as well as the technical properties of the crust leathers obtained were compared to verify if equivalent properties to those of the traditional unhaired leather could be obtained. Industrial scale runs were also performed, where the oxidative unhaired skins were mixed with traditional sulfide unhaired skins and submitted to traditional vegetable tannage/dyeingfatliquoring/finishing phases to verify the compatibility of the innovative unhairing procedure with the whole leather manufacturing process. The paper reports also the characterization of the exhaust water effluents and the results of scanning electron microscopy (SEM) used as an investigation method to better understand the mechanism of the oxidative unhairing in comparison with the traditional. 3

4 Experimental procedure The skin samples were supplied by tanneries belonging to the Tuscany (Italy) industrial leather district. The laboratory scale oxidative unhairing tests were conducted on pieces (15x20 cm, average weight 150 g) cut from the butt of heavy cattle skins (32+ kg) furnished by Conceria Volpi S.p.A. tannery. The process runs were conducted in cylindrical stainless steel laboratory drums (35 cm diameter, 20 cm length) rotating in a temperature controlled bath. The skins were initially soaked according to the recipe of Table 1 and unhaired according to the procedure of Table 2. The effect of the process parameters on the performance of the unhairing process was evaluated by visual observation of the skins (loss of hair, swelling, quality of the grain), by quantification of the swelling as weight percent increase of the sample, and by scanning electron microscopy (SEM) analysis using a JEOL 5600 LV microscope. The pilot-scale runs were conducted on medium calf skins (8-12 kg) furnished by UPIMAR tannery. The process runs were conducted in a polypropylene-coated pilot-scale drum (1 m diameter, 50 cm length). The skins, after soaking according to the recipe of Table 1, were divided in two sides: a few sides were unhaired and limed traditionally according to the recipe of Table 3, the corresponding sides were submitted to the oxidative unhairing according to the recipe of Table 4. After unhairing, the skins followed the traditional pickling/chrome tannage/dyeing-fatliquoring phases currently used to produce upper leathers. The industrial-scale runs were conducted on heavy cattle skins (32+ kg) furnished by Conceria Tempesti S.p.A. tannery. The skins, after the routine soaking phase performed in the tannery, were divided into two sides: a few sides were oxidative unhaired in the polypropylene-coated pilot-scale drum, the corresponding sides were unhaired traditionally in the tannery production line. The oxidative unhaired sides were redelivered to the tannery and reunited to the traditionally unhaired ones to follow two standard vegetable tannage/dyeing-fatliquoring/finishing cycles currently used by the tannery to produce leathers for two different upholstery applications. Either in the oxidative or in the traditional unhairing procedures, proteolytic enzyme based products were used in the preliminary stages of the process to loosen the softer proteins in the hair follicle. The final leathers obtained were characterized by their main physical, mechanical and technical properties. Physical testing was conducted according to Italian standards (UNI Characteristics and requirements of leather to be used in footwear industry ) for upper leather, while technical properties were assessed by the expertise personnel of Conceria Tempesti S.p.A. tannery. The shrinkage temperature was determined according to the UNI-ISO 3380 method using a Giuliani IG/TG/Theiss apparatus. The data reported are the mean of two determinations. The tearing load 4

5 was determined according to the UNI-ISO 3377 method using an electronic dynamometer (Pegasil, Model Marte). The data reported are the mean of three determinations. The grain distension was determined according to the UNI-ISO 3379 method using a lastometer (Pegasil, Model EL-51E). The data reported are the mean of three determinations. Results and discussion Oxidative unhairing by H 2 O 2 In the traditional hair destruction (burning) process, breaking down of the -S-S- bonds that characterize the keratin structure of the hair, is obtained by the use of a reducing agent (sodium sulfide or sulfhydrate), accompanied by the use of an alkali to hydrolyse the SH groups of the reduced proteins and promote their subsequent solubilization. Traditionally, the alkaline hydrolysis is accomplished by the use of lime. Hair removal by the combination of sulfides and lime can be greatly impaired by the application of excessive lime prior to the application of the sulfide, that cause the so-called phenomenon of hair immunization. In alkaline solution, the -S-S- bond may be broken (Fig. 1). Starting from the products of this reaction, different mechanism have been argued by leather technologists to explain how the protein side chains may recombine to prevent the reducing agent, subsequently added, from attacking the hair structure 15,16. Among the various hypotheses, the formation of transverse bonds between the bivalent Ca ++ ion and the products of dissociation of the S-S- bonds, appears quite respondent to the results of a comparative test conducted by using calcium and sodium hydroxide as alkaline agent, followed by the use of Na 2 S as unhairing agent, reported in Table 5. Immunization occurred when the hide was previously treated with calcium hydroxide for a prolonged time, but was not observed when using sodium hydroxide. The immunization seems to be promoted prevalently by the presence of bivalent ions that link the products of dissociation of the S-S- bond (Fig 2), rather than by the alkalinity of the solution, as suggested by several authors 14, but this hypothesis needs to be verified by a more detailed study and may represent an area of future research. The phenomenon of immunization is prevented by simultaneously adding lime and sulfides, and by taking advantage of the co-operative action of OH - and SH - ions that prevent immunization from occurring. When using H 2 O 2 for unhairing, the chemical attack of the S-S- bond occurs through a different mechanism (Fig. 3). The oxidative attack of the S-S- bond is due to the formation of peroxy anion from H 2 O 2 that occurs in highly alkaline medium. As observed by other authors 12, the attack of the S-S- bond by H 2 O 2 appears milder and slower in comparison with the reducing agents; H 2 O 2 is in fact effective in breaking only the softer keratin present in the root of the hair, while it leaves intact the stronger keratin of the shaft. For this reasons, the use of lime as alkaline agent is not feasible 5

6 because the immunization process would prevent the desired S-S- breaking of the hair root proteins. These observations are confirmed by the results of a comparative test conducted by using calcium and sodium hydroxide as alkaline agent, followed by the use of H 2 O 2 as unhairing agent, reported in Table 5. Immunization occurred when the hide was previously treated with calcium hydroxide for a prolonged time, but was not observed when using sodium hydroxide. These results suggest that the Ca ++ ions in solution may interpose in the -S-S- bridge causing the formation of an intermediate that cannot be attacked neither by H 2 O 2 nor by Na 2 S. As previously stated, these observations allows the formulation of a preliminary hypothesis, but the mechanism of the -S-Sattack either when using sulfides or hydrogen peroxide constitute an area of future research. The use of NaOH instead of Ca(OH) 2 is however accompanied by a higher degree of swelling of the collagenic structure 14. This is due to a) higher osmotic effect of Na + with respect to Ca ++ and b) the capacity of Ca ++ of cross-linking the carboxylic side sites of the collagenic fibrils to give a more packed structure. The control of the swelling of the hides during the oxidative unhairing represents a determining factor to obtain a final leather characterized by physical-mechanical properties comparable to those of traditional unhaired leather. Laboratory scale runs Preliminary laboratory scale runs were performed to investigate the optimal ph value to obtain an effective unhairing by H 2 O 2. As reported in Table 6, unhairing does not occur at ph values below 12, while the swelling degree shows a maximum at ph close to 12. At ph an increase of the swelling degree may be explained by the hydrolysis of the carboxylic groups with formation of Nacollagenate and the gradual decrease of the hydrogen inter-fibrillar bondings. The maximum swelling degree at ph 12 may be attributed to the complete hydrolysis. If ph is further increased above 12, the concentration of NaOH in the bath increases and, by osmotic effect, an increasing amount of water is rejected outside the hide, thus explaining the decrease of swelling. These results suggest an operative ph range of as the optimal to conduct the oxidative unhairing. Preliminary runs were also conducted to set out the optimal H 2 O 2 dosage, at ph As reported in Table 7, an effective unhairing is obtained by using dosages starting from 6% (salted weight). It must be noted that increasing the dosage of H 2 O 2 a higher quantity of NaOH must be dosed to obtain the same ph value. As a result, a slightly higher swelling degree was observed. Pilot scale runs According to the recipe reported in Table 4, the oxidative unhairing runs were repeated on pilot scale by varying the H 2 O 2 dosage in the range wt. % at ph In these runs, different from the laboratory scale, H 2 O 2 and NaOH were gradually dosed to minimize the swelling effects. The 6

7 pilot scale runs confirmed the results obtained on laboratory scale; unhairing was effective from 6% H 2 O 2 upwards. The SEM analysis of traditional and oxidative unhaired hides confirms the different mechanism of attack of the keratin structure by sulfides and hydrogen peroxide, as also reported by Shi et al. 12. As long as the process proceeds, H 2 O 2 gradually attacks the soft keratins of the hair root, leaving intact the stronger keratins of the shaft (Fig. 4.c); sulfides appear to exert a more energetic and rapid attack also on the stronger keratins of the shaft (Fig. 4.b). As a result of the different mechanism, the presence of residual roots in the follicles may be observed in the unhairing by sulfides (Fig. 4.b), while a complete removal of the hair from the follicle occurs by oxidative unhairing (Fig. 4.c). The higher swelling effect of NaOH in comparison with lime is evidenced in the SEM pictures of traditional and oxidative unhaired hides reported in Fig. 5. When using lime, a quite uniform fibril structure may be observed, while the use of NaOH is connected to the formation of compact bundles of fibrils, due to the compression effect derived from the higher swelling. As the dosage of H 2 O 2 (and, consequently of NaOH to maintain the ph level of 12.5) is decreased, a decrease of swelling may be observed. The unhaired hides, either the sides treated by 6-12 wt.% H 2 O 2 dosage or the sides treated by sulphides, followed the traditional chrome tannage/dyeing-fatliquoring phases currently adopted to produce upper leathers. The results of the physical-mechanical properties of the crust leathers are reported in Table 8. The tearing load of the oxidative crust leather, the grain distension and the shrinkage temperature of the oxidative unhaired leather, comply, on average, very well with the standards required for high quality chromium-tanned bovine upper leather. By a more detailed analysis of the tearing load curves (Fig. 6), the sulfide unhaired crust leather shows a lower elasticity that may be explained by a more hindered sliding of the fibrils due to the presence of a higher amount of protein inter-fibril residues, as evidenced by SEM analysis. The results of the assessment of the technical properties of the oxidative crust leathers, in comparison with the traditional unhaired leather, are reported in Table 9; a conventional scale of grades ranging from 1 (worst performance) to 5 (best performance) has been used. It may be observed that the crust leathers obtained by the oxidative and the traditional unhairing process show quite similar technical properties. At 6% H 2 O 2 dosage, a slight presence of residual keratin deposits on the grain was observed. This suggests that this is the minimum dosage to obtain a satisfactory unhairing. Table 10 reports the characterization of the exhaust baths of the oxidative process (average of the exhaust baths from 6-12 wt.% H 2 O 2 dosages) compared with exhaust bath from sulfide unhairing. 7

8 For a better comparison, in addition to the main pollutant concentrations, the amount of each single pollutant discharged is normalized on the basis of the salted skin weight. From Table 10, the major pollutants of the oxidative unhairing, either as absolute concentration or normalized with respect to the salted weight processed, appear quite similar to the traditional process. The evident advantage is obviously the complete absence of dissolved sulfides in the exhaust baths of the oxidative process. The polluting charge of the effluents may be easily handled in the industrial wastewaters systems that are usually dedicated to treat the tannery effluents. Finally, the absence of chromium (VI) assessed by analysis of the oxidative unhaired crust leather, indicates that the use of H 2 O 2 as oxidizing agent does not cause the oxidation of chromium (III) used in the tanning step. From the pilot scale run investigations, unhairing by H 2 O 2 appears a feasible process, either from the environmental or from the technical point of view, to produce high quality bovine upper leather. These results indicate a dosage of 9% H 2 O 2 is the optimal to assure complete unhairing and minimum swelling as well. Following the pilot scale investigation, the feasibility of the process was investigated on industrial scale. Industrial scale runs As reported in the experimental section, the skins, after the routine soaking phase performed in the tannery, were divided in two sides: a few sides were oxidative unhaired in the polypropylene-coated pilot-scale drum, the corresponding sides were unhaired traditionally in the tannery production line. The oxidative unhaired sides were redelivered to the tannery and reunited to the traditionally unhaired ones to follow two standard vegetable tannage/dyeing-fatliquoring/finishing phases currently used by the tannery to produce high quality bovine upper leathers to be used for two different upholstery applications. As reported in Table 11, the final leather obtained by the innovative unhairing process showed good physical-mechanical and technical properties, comparable with those of the traditional, and the leathers were assessed by the expert personnel of the tannery as satisfactory and suitable for their use in the production of high quality upper leathers. Besides, by the oxidative unhairing, the production of a versatile basis for different types of finite products is allowed. Conclusions The oxidative unhairing by hydrogen peroxide to produce high-quality bovine upper leather was first investigated on laboratory scale and validated on pilot and industrial scale. The results of the study assess the industrial feasibility of this innovative process, that allows the production of a versatile base for different types of finished products. The finished leathers are comparable to that 8

9 obtained by the traditional unhairing by sulfides and are characterized by good physical-mechanical and technical properties. The process is practical, economical to implement as well as compatible with the existing machinery. The elimination of sulfides from the beamhouse operations represents a significant improvement in the environmental impact of the leather industry and makes much more simple and economical the processes connected to the wastewater treatment. References 1 Aloy, M.; Tannerie et Pollution Centre Technique du Cuir, Lyon, German, H.P.; J. Am. Leather Chem. Ass. 92, 210, Money, C.A.; J. Soc. Leather Technol. Chem. 80, 175, Taylor, M.M., Bailey, D.G., Feairheller, S.H.; J. Am. Leather Chem. Ass. 82, 153, Cranston, R.W., Davis, M.H., Scroggie, J.G.; Leder 33, 49, Adewoye, R.O., Lollar, R.M.; J. Am. Leather Chem. Ass. 79, 446, Raju, A.A., Chandrababu, N.K., Samivelu, N., Rose, C., Rao, N.M.; J. Am. Leather Chem. Ass. 91, 115, Malathi, S., Chakraborty, R., Parthasarathi, K., Ramanaiah, B., Gupta, K.B., Mitra, R.B.; J. Am. Leather Chem. Ass. 86, 33, Paul, R.G., Mohamed, I., Davighi, D., Covington, A.D., Addy, V.L.; J. Am. Leather Chem. Ass. 96, 180, Morera, J.M., Bartoli, E., Borras, M.D., Munoz, D., Jimenez, J., Marsal, A.; J. Soc. Leather Technol. Chem. 81, 70, Marsal, A., Morera, J.M., Bartoli, E., Borras, M.D.; J. Am. Leather Chem. Ass. 94, 1, Shi, B., Lu, X., Sun, D.; J. Am. Leather Chem. Ass. 98, 185, Gehring, A.G., Bailey, D.G., DiMaio, R.L., Dudley, R.L., Marmer, W.N., Mazenko, C.E.; J. Am. Leather Chem. Ass. 98, 216, Marmer, W.N., Dudley, R.L., Gehring, A.G.; J. Am. Leather Chem. Ass. 98, 351, Caniglia, V., Maffè, S.; Chimica e tecnologia nella fabbricazione del cuoio, Levrotto & Bella, Torino (Italy), Manzo, G.; Chimica e tecnologia del cuoio, Media Service, Milano (Italy),

10 Captions for the figures Fig. 1. Attack of the keratin disulfide bond by alkali. Fig. 2. Cross-linking of the products of dissociation of the keratin bond by Ca ++ to give the hair immunization. Fig. 3. Attack of the keratin disulfide bond by H 2 O 2. Fig. 4. SEM pictures of a) untreated root and shaft hair, b) hair root and shaft attack by sulfides and grain status after unhairing, c) hair root and shaft attack by H 2 O 2 and grain status after unhairing. Fig. 5. SEM pictures of the collagenic structure after different dosages of H 2 O 2 compared with the collagenic structure after the traditional unhairing treatment. Fig. 6. Tearing load curve of the oxidative and of the traditional unhaired crust leathers obtained on pilot scale and correspondent SEM pictures of the collagenic structure. 10

11 Table 1. Steps of the soaking process (offers: wt.% based on salted weight). Desalting Soaking Water 25 C 200 % Antibacterial 0.2 % Surfactant 0.1 % 30 min Drain under drumming 1 Water 25 C 80 % Basifying agent (MgO content: >96 wt. %) 0.5 % Antibacterial 0.3 % Polyfosfate 0.2 % Surfactant 0.2 % 30 min Automatic drumming for 24 h (5 min of rotation/h) 1. performed only in the pilot-scale runs Table 2. Steps of the oxidative unhairing process on laboratory scale (offers: wt.% based on salted weight). Unhairing The process is performed in the soaking bath Proteolytic enzyme based product (enzyme content >95 wt.%) 0.3 % 60 min Proteolytic enzyme based product (enzyme content >95 wt.%) 0.5 % 30 min H 2 O 2 (34% w/w) % 6 9 % 3 h Automatic drumming for 24 h (5 min of rotation/h) Drain Table 3. Steps of the sulfide unhairing process (offers: wt.% based on salted weight). Unhairing The process is performed in the soaking bath Proteolytic enzyme based product (enzyme content >95 wt.%) 0.3 % 60 min Antiwrinkle product 2 % Proteolytic enzyme based product (enzyme content >95 wt.%) 0.15 % 30 min NaHS flakes 1.5 % Na 2 S flakes 2.8 % Ca(OH) 2 powder 1 % 90 min Ca(OH) 2 powder 3 % Polyphosphate 0.2 % 1 h Automatic drumming for 24 h (5 min of rotation/h) Drain under drumming 11

12 Table 4. Steps of the oxidative unhairing process on pilot scale (offers: wt.% based on salted weight). Unhairing The process is performed in the soaking bath Proteolytic enzyme based product (enzyme content >95 wt.%) 0.3 % 60 min Proteolytic enzyme based product (enzyme content >95 wt.%) 0.5 % 30 min runs at 4.5% H 2 O 2 offer: H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 1.5 % 25 min runs at 6 % H 2 O 2 offer: H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min runs at 9 % H 2 O 2 offer: H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min runs at 12 % H 2 O 2 offer: H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min H 2 O 2 (34% w/w) 3 % 25 min For each run, at the end of H 2 O 2 and NaOH addition: Automatic drumming for 24 h (5 min of rotation/h) Drain 12

13 Table 5. Effect on the hair of 24 hours treatment with calcium or sodium hydroxide as alkaline agents in oxidative and traditional unhairing. Alkaline agent (dosed until ph 12; 24 hours drumming) Unhairing agent (24 hours drumming) Ca(OH) 2 NaOH Na 2 S Immunization Hair burning H 2 O 2 Immunization Hair burning Table 6. ph effect of the oxidative unhairing baths on the unhairing and swelling degree of the hides (offers: 9 wt.% of H 2 O 2 based on salted weight, recipe of Tab. 3). ph Unhairing degree % Swelling 11 ξ ξ ξ: not satisfactory : good Table 7. Oxidative unhairing at different dosages of H 2 O 2 (recipe of Tab. 3, ph 12.5). H 2 O 2 dosage Unhairing degree (% on salted weight) 4.5 ξ ξ: not satisfactory : good 13

14 Table 8. Physical-mechanical properties of the crust leather obtained on pilot scale. Oxidative unhaired crust leather Sulfides unhaired H 2 O 2 dosage crust leather (wt. % on salted skin) Test UNI guidelines Tearing load (N) ISO 3377 method 54±2 58±2 46±2 55±2 50 Grain distension (mm) UNI ISO 3379 method 8.7± ± ± ±0.2 7 Shrinkage temperature ( C) 99±1 99±1 96±1 97±1 Table 9. Technical properties of the crust leather obtained on pilot scale. Oxidative unhaired crust leather Sulfides unhaired H 2 O 2 dosage crust leather (wt. % on salted skin) Technical properties Grain quality Roundness Fullness Absence of wrinkles Softness Grain stability

15 Table 10. Comparison between the polluting charge of the exhaust bath of the oxidative and the sulfides unhairing processes. Pollutants (g/m 3 )* COD Chlorides Sulfates Suspended Nitrogen Sulfides (as Cl - ) (as SO 2-4 ) Solids (as NH + 4 ) (as S 2- ) Oxidative unhairing Sulfides unhairing Pollutants (kg/t salted skin)* COD Chlorides Sulfates Suspended + NH 4 Sulfides (as Cl - ) (as SO 2-4 ) Solids (as N) (as S 2- ) Oxidative unhairing Sulfides unhairing * average of three determinations, ± 5% Table 11. Physical-mechanical and technical properties of the final leather obtained on industrial scale. Oxidative Sulfides UNI unhaired leather unhaired leather guidelines Physical-Mechanical Tests Run 1 Run 2 Run 1 Run 2 Tearing load (N) ISO 3377 method 192±2 245±2 166±2 233±2 50 Grain distension (mm) UNI ISO 3379 method 8.2± ± ± ±0.2 7 Technical properties Grain quality Roundness Fullness Absence of wrinkles Softness Grain stability

16 OH - R S S R H 2 O R SOH R SH Fig.1 R SOH Ca HS R R SO Ca S R + 2 H + Fig. 2 H 2 O 2 HOO - + H + Fig. 3 16

17 a) b) c) 5 min Fig. 4 1 hr 2 hr 2 hr Hair shaft Hair root 17 Follicle

18 H 2 O 2 12% H 2 O 2 9% H 2 O 2 6% Fig. 5 18

19 Tearing load (N) Strain (mm) Traditional Oxidative 12% Fig. 6 19

20 20