Aus der Praxis für die Praxis 1 Introduction The demand for longer-lasting, better performing, lower maintenance metalworking fluids (MWFs) has never been greater. Reducing the frequency of tank-side maintenance and extending the time between shut-downs, can reduce the cost of fluid ownership and increase productivity. At the same time, regulatory requirements, health and safety considerations and customer preferences are limiting the ingredients considered acceptable, particularly for MWFs intended for use in multiple geographies. An important multi-functional additive, boric acid, has been used as a cost-effective, biostatic corrosion inhibitor and pH stabilizer since the early 1980s [1]. However, in 2010 the European Classification, Labelling and Packaging (CLP) regulation took effect, and under this regulation boric acid is classified as toxic to reproduction, Category 1B. Boric acid has been added to the European Union’s candidate list of Substances of Very High Concern (SVHC), and its use is limited to less than 5.5 % by weight in MWF concentrates. Although boric acid can be effective below this dosage, depending on the dilution rate, its classification as a reproductive toxicant has caught the attention of the industry. As a result, it is possible that some fluid producers and end users may decide not to allow any amount of boric acid. Formaldehyde-condensate biocides, in particular GRO- TAN ® (hexahydro-1,3,5-tris-(2-hydroxyethyl)-s-triazine), have been the bacteriacides of choice for water-dilutable MWFs for several decades. Triazine and another major class of formaldehyde condensates, the oxazolidines, provide cost effective control of prominent gram negative bacteria, such as Pseudomonas aeruginosa. These biocides are also relatively stable at the alkaline pH of most MWF concentrates. Unfortunately, formaldehyde condensate biocides also have the potential to release formaldehyde under MWF use conditions, and the International Agency for Research on Cancer (IARC) and National Toxicology Program (NTP) consider formaldehyde to be a known human carcinogen [2,3]. In view of industry concerns with formaldehyde and, by association, formaldehyde condensate biocides, 42 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 * Bonnie A. Pyzowski, Certificate in Chemistry Nicole L. Webb, B.Sc. Microbiology Patrick E. Brutto, M.Sc. Chemistry ANGUS Chemical Company Buffalo Grove, Illinois USA Robert M. Stubbs, B.Sc. Pure Chemistry Sea-Land Chemical Europe Byley Cheshire, United Kingdom Meeting Metalworking Fluid Longevity Requirements without Boron, Formaldehyde Condensates and Secondary Amines B. Pyzowski, N. Webb, P. Brutto, R. Stubbs* Water dilutable metalworking fluids are susceptible to shortened fluid life, due to the presence of numerous species of bacteria and fungi. Fluids have therefore been formulated with components which control microorganisms and/ or resist biological degradation. Examples include formaldehyde condensate biocides like GROTAN® (78 % hexahydro-1,3,5-tris-(2-hydroxyethyl)-s-triazine), boric acid or boron condensates, and secondary amines like dicyclohexylamine (DCHA). Regulatory actions and fluid end user preferences, driven primarily by health, safety and environmental concerns, are leading the industry to reduce or eliminate the use of these classes of compounds, at least in some countries. Maintaining fluid performance and longevity in the presence of microorganisms is more challenging when some or all of these compounds are eliminated. This paper discusses the use of certain primary amino alcohols, in combination with non-formaldehyde releasing biocides, and compares performance with systems containing 0-5 % boric acid and GROTAN, or DCHA and non-formaldehyde biocides, in the presence of hydraulic oil contamination. The performance of a high oil semi-synthetic fluid with 2.5 % boric acid and 2 % GROTAN is easily exceeded using DCHA or a primary amino alcohol combination (2-amino-1-butanol, 2-amino-2ethyl-1,3-propanediol and 3-amino-4-octanol), together with several non-formaldehyde biocides. Additionally, the primary amino alcohol combination with certain non-formaldehyde biocides approaches the performance of 5 % boric acid and 2 % GROTAN. Keywords Metalworking, bioresistance, boric acid, formaldehyde, secondary amines, primary amines, longevity Abstract T+S_1_17 13.12.16 07: 53 Seite 42 Aus der Praxis für die Praxis one major biocide manufacturer, The Dow Chemical Company, has decided not to reregister a product used for many years in the MWF industry, BIOBAN™ CS- 1246. The request for cancellation was acknowledged by the United States Environmental Protection Agency in July, 2014 [4]. Dicyclohexylamine (DCHA) has been used for several years to extend fluid life. However, although exempt from regulation in Germany under TRGS 611 due to its N-nitrosamine being considered non-carcinogenic, DCHA has the following GHS hazard classifications in the European Union: H301 (toxic if swallowed), H311 (toxic in contact with skin) and H410 (very toxic to aquatic life with long lasting effects) [5]. Some MWF producers and users have therefore decided not to allow the use of DCHA in their fluids. This paper will explore the use of alternative amino alcohols and registered biocides, with the goal of matching or exceeding the performance of generic fluids containing boric acid, GROTAN and/ or DCHA. 2 Experimental The following MWF formulations and test protocols were used in this study. 2.1 Semi Synthetic MWF Formulations High oil semi-synthetic MWF formulations were prepared for this study (Figure 1); this is a typical fluid class in Western Europe. The formulations are divided into four groups: • Fluids 1-3 contain 0-5 % boric acid, 2 % GROTAN and monoethanolamine (MEA) plus triethanolamine (TEA) for neutralization and pH adjustment/ buffering. These fluids served as “controls” in this study. • Fluids 4-8 include a primary amine stream (PAS) containing 2-amino- 1-butanol and 2-amino-2-ethyl-1,3propanediol, and the following nonformaldehyde biocides: ROCIMA™ BT2S (20 % benzisothiazolinone), BIOBAN™ P-1487 (4-(2-nitrobutyl)-morpholine and 4,4’-(2-ethyl- 2-nitrotrimethylene) dimorpholine), DOWICIDE™ 1E (o-phenylphenol) and Densil™ DN (n-butyl-1,2-benzisothiazolinone). DOWANOL™ EPh (phenoxyethanol) is not a registered biocide, but has synergistic preservative properties, for example in cosmetics formulations [6]. • Fluids 9-13 contain DCHA, MEA for neutralization/ pH adjustment and the same biocides as Fluids 4-8. A different organic acid is required to achieve stable fluid concentrates, due to the lipophilic nature of DCHA and its corresponding salts. • Fluids 14-18 contain PAS and CORRGUARD™ EXT (~85 % 3-amino-4-octanol), along with the same nonformaldehyde biocides. As with DCHA, the less hydrophilic character of CORRGUARD EXT and its salts requires a different acid to achieve stable concentrates. 2.2 Microbiological Challenge Test Protocol A modified ASTM E2275 procedure was used for the microbiological challenge tests. A mixed bacterial/ fungal inoculum was isolated from spoiled MWFs obtained from fluid producers in the USA. The fresh fluid concentrates were diluted to 5 % using Chicago tap water containing approximately 125 ppm total hardness. The diluted fluids were placed into Erlenmeyer flasks followed by cast iron chips, and then an inoculum of 10 6 colony forming units (CFU) per mL bacteria and 10 4 CFU/ mL fungi was added. Fresh hydraulic oil was also added (5 % on weight of diluted fluid), and the flasks were then sealed with foam caps and placed on orbital shakers. Shaking was continued for approximately 104 hours, following by shutdown for approximately 64 hours. After conclusion of the shutdown period, tramp oil was removed using an inert absorbent material and the fluids were sampled to determine bacterial and fungal counts using a serial dilution/ plate count method. After sampling, the fluids were re-inoculated with bacteria and Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 43 Ingredient Fluid ---> 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 CORFREE® M1 1 3 1.4 0.6 3 3 3 3 3 Diacid 1550 2 4 4 4 4 4 4 4 4 4 4 Boric Acid 0 2.5 5 Deionized Water 21.5 21 19.6 21.2 21.6 22 19.1 23.7 22.1 21.9 21 21.8 23.3 21.6 21.1 21.1 20.4 22.1 Primary Amine Stream (PAS) 3 8.2 8.4 8.4 8.4 8.4 2.4 2.9 2.6 2.4 2.4 CORRGUARD EXT 3 6 6 6 6 6 Triethanolamine 5 5 5 Monoethanolamine 4.4 4.4 4.4 1.2 1.7 1.5 1.2 1.4 DCHA 6 6 6 6 6 Hydrocal 100 4 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 40 Petronate HL 5 10 10 10 10 10 10 10 10 10 10 10 10 11 10 10 10 10 11 MWV L-5 2 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Emulsogen MTP 070 6 4 4 4 4 4 4 4 4 4 4 5 4 4 4 4 4 4 4 Polartech PE 2110 7 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 2.4 DOWANOL™ PnB 8 3 3 3 3 3 2.1 0 3 3 3 2.1 3 3 3 2.1 3 Oleyl Alcohol 0.7 0.3 2.2 1.6 1.1 3.1 1.2 1.3 1 1 0.6 0.6 0.6 0.6 0.8 0.8 0.8 GROTAN® 9 2 2 2 ROCIMA™ BT2S 8 2 2 2 BIOBAN™ P-1487 8 2 2 2 DOWICIDE™ 1E 8 (70% in DOWANOL PnB) 3 3 3 DOWANOL EPh 8 6 6 6 Densil™ DN 10 0.3 0.3 0.3 TOTAL 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 1 Invista ; 2 Ingevity ; 3 ANGUS Chemical Company ; 4 Calumet Refining ; 5 Sonneborn ; 6 Clariant ; 7 Afton Chemical ; 8 Dow Chemical ; 9 Troy Corp ; 10 Lonza Figure 1: Semi-Synthetic MWF Formulations T+S_1_17 13.12.16 07: 53 Seite 43 Aus der Praxis für die Praxis fungi and 5 % fresh tramp oil was added. This cycle was repeated until failure, defined as two consecutive weeks above 10 5 CFU/ mL bacteria or 10 3 CFU/ mL fungi. 2.3 pH Monitoring A significant change in the pH of an in service fluid can be an indicator of microbiological degradation. Most often the pH will decrease due to the generation of acidic biodegradation products, but pH can also increase due to alkaline biodegradation products. In the present study, the pH of each fluid was measured initially and weekly thereafter during microbiological challenge testing. 2.4 Cast Iron Corrosion Test Protocol Loss of cast iron corrosion control can be an indicator of microbiological growth. In our study, a small sample of fluid was removed periodically from each flask during microbiological challenge testing, to determine corrosion control of standard cast iron chips. A modified ASTM D4627 procedure was used, where 3.0 grams of chips were placed on white filter paper in a petri dish, followed by addition of 5 grams of fluid to completely immerse the chips. The dish was covered for two hours and the fluid removed using a pipette. The wet chips were dried on the filter paper at 25 °C and 65 % relative humidity for approximately 24 hours. The percent staining of the filter paper was then estimated. 2.5 Aluminum Staining Test Protocol Staining of aluminum alloys can occur due to interaction with various fluid components, including certain amines and acids. The higher the fluid alkalinity and pH, the greater the chance of staining. In the present study, aluminum staining properties were determined by fully immersing freshly-sanded coupons of alloys 2024, 356, 6061 and 7075 in the freshly diluted fluids (5 % in tap water). The specimens were rough-sanded using 60 grit paper (Al 2 O 3 ), and then fine-sanded using 120 grit paper. The coupons were exposed for 24 hours at 40 °C, and staining was rated on a scale of 0 to 5, with 0 indicating similar appearance to the unexposed coupon, and 5 indicating dark or white stains on the majority of the coupon surface. 2.6 Residue Rinsability Test Protocol The residue left by in-service fluids on machines and parts can create cleaning difficulties and other problems. It is desirable for residues to be soft and easily removed using water. To test for rinsability, 2 g of diluted fluid (5 % in tap water) was placed in a small glass petri dish and dried at 50 °C for 24 hours. After cooling, 4 g of tap water was added to the dish and allowed to soak for 3 minutes. The dish was then swirled in a circular motion by hand for 2 minutes, inverted for 2 minutes to drain, and air dried with the open side up. Each fluid was tested in duplicate and the amount of residue estimated visually on a scale of 0 (least) to 3 (most). 3 Results and Discussion 3.1 Microbiology Results Bacterial results for the control fluids with GROTAN and 0-5 % boric acid, versus those with the primary amine stream (PAS) and non-formaldehyde biocides, are presented in Figure 2. The data show early bacterial failure for fluids with 0-2.5 % boric acid. The boron-free fluid with PAS and ROCIMA BT2S resists bacterial attack for an additional 4-5 weeks, and a similar fluid with PAS and Densil DN resists bacteria for 13 weeks. The fluid with GROTAN and 5 % boric acid, as well as those with PAS and the other non-formaldehyde biocides, resist bacterial attack through 15 weeks. Fungal challenge results for the controls vs. the fluids with PAS and non-formaldehyde biocides are presented in Figure 3. The fluids with GROTAN and 0-2.5 % boric acid lose fungal control early, but increasing the boric acid to 5 % prevents growth through 15 weeks. All fluids with PAS fail early, except that with Densil DN which resists fungi until 9 weeks. Results for the fluids with GROTAN and 0-5 % boric acid, versus those with DCHA and the non-formaldehyde 44 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 Figure 2: Bacterial Results - PAS vs. Controls Figure 3: Fungal Results - PAS vs. Controls T+S_1_17 13.12.16 07: 53 Seite 44 Aus der Praxis für die Praxis biocides, are presented in Figures 4 and 5. Fluids 9, 10 and 12 with DCHA and ROCIMA BT2S, BIOBAN P- 1487 and DOWANOL™ EPh resist bacterial degradation longer than the fluids with GROTAN and 0-2.5 % boric acid, but not nearly as long as the fluid with 5 % boric acid. Fungal resistance of the fluids containing DCHA is better than those with GROTAN and 0-2.5 % boric acid, but only the fluid with DCHA and Densil DN approaches the performance of the fluid with 5 % boric acid. Results for the control fluids versus those with COR- RGUARD™ EXT and non-formaldehyde biocides are presented in Figures 6 and 7. The fluids with COR- RGUARD EXT resist bacterial growth better than those with GROTAN and 0-2.5 % boric acid, however only the fluid with CORRGUARD EXT and ROCIMA BT2S resists bacterial attack as well as that with 5 % boric acid. All fluids with CORRGUARD EXT resist fungal attack better than those with GROTAN and 0-2.5 % boric acid, and those with CORRGUARD EXT and RO- CIMA BT2S or DOWANOL EPh come closest to matching the performance of the fluid with 5 % boric acid. 3.2 pH Stability Results Changes in fluid pH can indicate microbiological degradation and loss of performance. The pH data taken during microbial challenge tests are presented in Figures 8-10, and are generally consistent with the microbiological results; the fluids with PAS have better pH stability than the authors would have predicted from the microbial data. The control fluids with GROTAN and 0-2.5 % boric acid lose pH control much faster than that with 5 % boric acid. Most fluids with PAS and the nonformaldehyde biocides have similar pH stability to the fluid with 5 % boric acid, except the one with ROCIMA BT2S which loses control after 9 weeks. The fluids with DCHA lose pH control relatively quickly, especially those with DOWICIDE 1E and Densil DN. This could be Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 45 Figure 4: Bacterial Results - DCHA vs. Controls Figure 5: Fungal Results - DCHA vs. Controls Figure 6: Bacterial Results - CORRGUARD EXT vs. Controls Figure 7: Fungal Results - CORRGUARD EXT vs. Controls Figure 8: pH Results - PAS vs. Controls T+S_1_17 13.12.16 07: 53 Seite 45 Aus der Praxis für die Praxis partially due to migration of DCHA into the tramp oil and/ or loss by evaporation. The fluids with CORRGU- ARD EXT have better pH stability than those with DCHA, although the pH of the fluid with Densil DN decreases rapidly after 9 weeks. CORRGUARD EXT has been shown in previous ANGUS studies to partition much less into tramp oil than DCHA, which could be one reason for the improved pH stability (and better microbiological control). 3.3 Cast Iron Corrosion Results Results for cast iron corrosion control during microbiological challenge testing are shown in Figures 11-13. Testing of the fluids with GROTAN and 0-2.5 % boric acid was stopped after 4 weeks due to poor microbial control, so corrosion data are not available beyond this point. Good corrosion control is observed for the control with 5 % boric acid through 13 weeks. Fluids with PAS and the alternative biocides lose corrosion control after 8 weeks, except the fluid with ROCIMA BT2S which loses control after 4 weeks. Most of the fluids with DCHA lose corrosion control at 8-13 weeks, although Fluid 10 with BIOBAN P-1487 performs a little better than the others. The fluids with CORRGUARD EXT control corrosion through 8 weeks, and those with DOWICIDE 1E and Densil DN perform close to the fluid with 5 % boric acid through 13 weeks. The fluid with 5 % boric acid performs best after 16 weeks. 3.4 Aluminum Staining Results Staining results for four common aluminum alloys are presented in Figure 14. Only the controls (Fluids 1-3) caused discoloration of the alloys, which could be due to the combined effects of MEA, TEA, GROTAN and their associated salts. The authors are not aware of boric acid having a negative impact on aluminum alloys. 46 Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 Figure 9: pH Results - DCHA vs. Controls Figure 10: pH Results - CORRGUARD EXT vs. Controls Figure 11: Corrosion Results - PAS vs. Controls Figure 12: Corrosion Results - DCHA vs. Controls Figure 13: Corrosion Results - CORRGUARD EXT vs. Controls T+S_1_17 13.12.16 07: 53 Seite 46 Aus der Praxis für die Praxis 3.5 Residue Rinsability Results Results of the residue rinsability tests are shown in Figure 15. The fluids with 2.5-5 % boric acid had better rinsability than the fluid without boric acid; this surprised the authors because reaction products of boric acid (amine salts, etc.) can produce hard, sticky residues. Most of the other fluids rinsed off easily, with the exception of Fluids 4 & 5 containing PAS and Rocima BT2S or BIOBAN P-1487; it seems the biocide influenced rinsability more than PAS, since Fluids 6-8 rinsed easily. The authors believe the high oil content of the semi-synthetic formulations had a beneficial effect on residue removal, which could explain why residues of the fluids with boric acid were easily rinsed. Unfortunately, this doesn’t explain why the residues of Fluids 1, 4 and 5 (without boric acid) were more difficult to remove than the others. 4 Conclusions The performance of a semi-synthetic fluid containing 2.5 % boric acid is easily exceeded using DCHA or a primary amine combination (PAS/ CORRGUARD EXT), together with several non-formaldehyde biocides. Additionally PAS/ CORRGUARD EXT enables performance approaching 5 % boric acid/ 2 % GROTAN, in a formulation free of boric acid, formaldehyde condensates and DCHA. Cost, performance and environmental/ safety requirements will dictate whether the alternatives presented in this paper are viable for MWF formulators and users requiring fluids without boric acid, secondary amines and formaldehyde condensate biocides. 5 Acknowledgements The authors would like to acknowledge and thank Soraya Kraszczyk of ANGUS Chemical Company for her help generating the data supporting this paper. References [1] Anderson, S., Determination of residual free boric acid in amine borate condensation reaction products by 11 B NMR spectroscopy, Lube Magazine, 110, 21-24, 2012 [2] IARC Press Release No. 153, 2004 [3] NTP, Department of Health and Human Services, 12 th Report on Carcinogens, 2011 [4] Federal Register Volume 79, Number 136, 41553-41554, 2014 [5] BASF safety data sheet according to Regulation (EC) No. 1907/ 2006, Version 9.0, Revised: 06.06.2014 [6] Dow Oxygenated Solvents Technical Data Sheet, Form No. 110-01140-607AMS Tribologie + Schmierungstechnik 64. Jahrgang 1/ 2017 47 Alloy 356 Alloy 2024 Alloy 6061 Alloy 7075 Fluid 1 3 0 2 2 Fluid 2 3 1 3 2 Fluid 3 3 1 2 2 Fluid 4 0 0 0 0 Fluid 5 0 0 0 0 Fluid 6 0 0 0 0 Fluid 7 0 0 0 0 Fluid 8 0 0 0 0 Fluid 9 0 0 0 0 Fluid 10 0 0 0 0 Fluid 11 0 0 0 0 Fluid 12 0 0 0 0 Fluid 13 0 0 0 0 Fluid 14 0 0 0 0 Fluid 15 0 0 0 0 Fluid 16 0 0 0 0 Fluid 17 0 0 0 0 Fluid 18 0 0 0 0 Staining Rating Figure 14: Aluminum Staining Results - Controls vs. Others Residue Rinsability (Rating) Fluid 1 2 Fluid 2 0 Fluid 3 0 Fluid 4 3 Fluid 5 3 Fluid 6 0 Fluid 7 0 Fluid 8 0 Fluid 9 1 Fluid 10 1 Fluid 11 1 Fluid 12 1 Fluid 13 1 Fluid 14 1 Fluid 15 1 Fluid 16 0 Fluid 17 0 Fluid 18 0 Figure 15: Residue Rinsability - Controls vs. Others Aktuelle Informationen über die Fachbücher zum Thema „Tribologie“ und über das Gesamtprogramm des expert verlags finden Sie im Internet unter www.expertverlag.de Anzeige T+S_1_17 13.12.16 07: 53 Seite 47