CÁCH KIỂM TRA NỒNG ĐỘ DẦU CẮT GỌT KIM LOẠI PHA NƯỚC KHI PHA

1. CÓ MẤY LOẠI DẦU CẮT GỌT KIM LOẠI PHA NƯỚC?

Dầu cắt gọt kim loại pha nước hay còn gọi là dầu sữa hoặc nước làm mát. Về bản chất dầu cắt gọt kim loại được chia làm 03 loại chính:

- Dầu sữa (Soluble Oil): sau khi pha nước sẽ như sữa.

- Dầu cắt gọt tổng hợp (Fully-synthetic MWF): sau khi pha nước sẽ trong mờ đến như nước.

- Dầu cắt gọt bán tổng hợp (Semi-synthetic MWF). Trong đó dầu cắt gọt kim loại bán tổng hợp được chia làm 03 loại: dầu cao, dầu trung và dầu thấp. 

    + Hàm lượng dầu cao sẽ thì dung dịch sau khi pha sẽ như dầu sữa, song kích thước hạt và khả năng tẩy rửa cũng như chống gỉ tốt hơn dầu sữa. 

    + Hàm lượng dầu trung thì dung dịch sau khi pha sẽ có màu trong mờ, kiểu như nước vo gạo.

    + Hàm lượng dầu thấp thì dung dịch sau khi pha sẽ có màu trong mờ, kiểu như nước vo gạo đến trong suốt như nước.

Đó là cách căn bản dễ hiểu để phân biệt dầu cắt gọt và gia công kim loại pha nước (sau đây gọi chung là dầu cắt gọt). Ngoài ra, việc phân loại dầu cắt gọt còn có thể dựa vào kích thước hạt nhũ như

- Dầu sữa: kích thước hạt từ 2.0 đến 50 micromet.

- Dầu bán tổng hợp: kích thước hạt từ 0.1 - 2.0 micromet cho hàm lượng dầu cao, 0.01-0.1 micromet cho các loại còn lại.

- Dầu tổng hợp: kích thước dưới 0.003 micromet.

Tuy nhiên việc phân loại dầu cắt gọt dựa trên hàm lượng dầu bên trong thường như sau:

- Dầu sữa: 70-80% dầu gốc.

- Dầu bán tổng hợp: 5-60% dầu gốc.

- Dầu tổng hợp: không chứa dầu gốc.

2. DẦU CẮT GỌT BÁN TỔNG HỢP VÀ TỔNG HỢP CÓ PHẢI DÙNG DẦU GỐC TỔNG HỢP?

Như định nghĩa ở trên, không có sự liên quan giữa dầu gốc tổng hợp nhóm IV (PAO) và V (ESTERS) trong cách phân loại dầu cắt gọt kim loại. 

3. NỒNG ĐỘ DẦU CẮT GỌT KIM LOẠI TRONG NƯỚC

Chú ý: Thuật ngữ "nồng độ dầu" thường được các thợ máy và kỹ sư vận hành máy hiểu là lượng dầu cắt gọt có trong dung dịch sau khi pha. Chứ không phải là "nồng độ của dầu gốc" trong dung dịch sau khi pha nhé. Muốn phân tích lượng dầu gốc trong dung dịch sau khi pha, mình sẽ trao đổi trong bài viết khác.

Nồng độ dầu có thể là tỉ lệ thể tích hay tỉ lệ khối lượng, do đó cần phải xem xét kỹ nó là nồng độ thể tích hay khối lượng. Đứng về góc nhìn khoa học và hoá học, mình luôn khuyến khích sử dụng khối lượng thay vì thể tích do: 

- Khi trộn hai chất vài nhau thì thể tích sẽ thay đổi và khối lượng không thay đổi.

- Thể tích nếu không để ý sẽ rất bị sai, do nếu tồn tại các bọt nhỏ li ti bên trong chất lỏng thì thể tích thực của chất lỏng sẽ nhỏ hơn thể tích thực của chất lỏng chứa bọt khí li ti. Trong khi đó, khối lượng lại không thay đổi trong cả hai trường hợp. 

3.1. XÁC ĐỊNH NỒNG ĐỘ DẦU SAU KHI PHA NƯỚC BẰNG KHÚC XẠ KẾ

Nồng độ dầu được xác định = giá trị đọc được trên khúc xạ kế x với hệ số hiệu chỉnh 

Cách xác định hệ số hiệu chỉnh:

Thường sẽ thiết lập đồ thị tương quan giữa nồng độ dầu (trục tung) và giá trị đọc được trên khúc xạ kế (trục hoành) như đồ thị bên dưới. Sau đó, hệ số hiệu chỉnh chính là hệ số góc của đồ thị.

ĐỒ THỊ TƯƠNG QUAN GIỮA NỒNG ĐỘ DẦU VÀ GIÁ TRỊ ĐỌC TRÊN KHÚC XẠ KẾ

Sẽ có một chút sai số giữa việc sử dụng khúc xạ kế máy và cầm tay trong đồ thị trên, do mình sử dụng cân điện tử sai số 0.1g. Thêm vào đó, việc xác định giá trị trên khúc xạ kế cầm tay đôi lúc cũng làm sai lệch một tý kết quả đo. Song, cả hai đồ thị đều cho ta thấy hệ số hiệu chỉnh có giá trị gần như = 1. Kết quả này có được từ công thức dầu cắt gọt bán tổng hợp hàm lượng dầu trung. Do đó, việc dựa trên hệ số hiệu chỉnh để đoán đó là loại dầu nào thường chỉ có giá trị tham khảo, không hoàn toán chính xác.

Thông thường, đối với người dùng cuối thì hệ số hiệu chỉnh này sẽ được cung cấp kèm với tài liệu kỹ thuật (TDS hay PDS) của dầu. Nếu nhà cung cấp không cung cấp, người dùng cuối cũng có thể tự khảo sát như trên để xác định giá trị này. CHÚ Ý: HỎI LẠI NHÀ SẢN XUẤT LÀ VIỆC KHẢO SÁT DỰA TRÊN NỒNG ĐỘ KHỐI LƯỢNG HAY THỂ TÍCH. VÌ NỒNG ĐỘ KHỐI LƯỢNG HAY THỂ TÍCH KHÁC NHAU, HỆ SỐ HIỆU CHỈNH SẼ KHÁC. DẪN ĐẾN SAI SỐ TRONG VIỆC PHA DẦU.

Khi hệ số hiệu chỉnh = 1: nghĩa là nồng độ là giá trị đọc được trên khúc xạ kế.

Khi hệ số hiệu chỉnh >1: vui lòng nhân hệ số hiệu chỉnh với giá trị đọc được để có được nồng độ chính xác.

3.2. VÌ SAO VIỆC XÁC ĐỊNH NỒNG ĐỘ DẦU NGAY SAU KHI PHA LÀ QUAN TRỌNG?

Việc xác định chính xác nồng độ pha rất qua trọng trong sản xuất, vì nó sẽ ảnh hưởng đến quá trình chống gỉ trong lúc gia công. Mỗi một loại dầu cắt gọt khác nhau sẽ có giá trị break point khác nhau. Break Point là điểm mà tại đó dầu bị gỉ không quá 5% nồng độ theo phương pháp IP 287. Khi sử dụng dung dịch có nồng độ thấp hơn Break Point, nguy cơ gỉ sẽ rất dễ xảy ra, đặc biệt trong quá trình gia công thép đen và gang.

PHƯƠNG PHÁP KIỂM TRA IP 287

3.3. CÓ THỂ XÁC ĐỊNH NỒNG ĐỘ DẦU CỦA DUNG DỊCH ĐANG SỬ DỤNG

Đối với dầu sữa hay bán tổng hợp thì dù muốn hay không nồng độ dầu sẽ thay đổi. Có thể tăng hoặc giảm tuỳ thuộc vào nhiều yếu tố. Ví dụ: việc nước bay hơi làm tăng nồng độ dầu, nhưng việc dầu bám vào chi tiết khi gia công sẽ làm giảm nồng độ dầu. Do đó, khi nồng độ dầu tăng hay giảm đều ảnh hưởng đến quá trình gia công về nhiều khía cạnh. Do đó bằng việc kiểm tra nồng độ trên khúc xạ kế so với giá trị ban đầu (chưa sử dụng) có thay đổi hay không. Nếu giảm thì châm thêm dung dịch với nồng độ > hơn nồng độ ban đầu hoặc nếu lớn hơn thì phải thêm dung dịch với nồng độ loãng hơn ban đầu (chú ý không được sử dụng nước mà phải dùng dụng dịch với nồng độ loãng hơn), mục tiêu là điều chỉnh về đúng nồng độ ban đầu yêu cầu.

3.4. NỒNG ĐỘ DẦU CẮT GỌT CỦA DẦU BỊ LẮNG?

Việc dầu cắt gọt bị lắng là một quá trình động học diễn ra rất chậm mà mắt thường không nhìn thấy được, đến khi chúng xảy ra thì hầu như toàn bộ phụ gia sẽ lắng ở đáy và dầu sẽ ở trên. Khi đó, việc kiểm tra nồng độ dầu sẽ bị sai số so với khuyến cáo của nhà sản xuất. Khi đó, bạn có cơ sở để nghi ngờ dầu cắt gọt của bạn bị lắng nếu như bạn chắc chắn rằng: bạn dùng đúng nồng độ (khối lượng hay thể tích), nước máy, hiệu chuẩn khúc xạ kế trước khi đo,... thì xin vui lòng kiểm tra phuy dầu cắt gọt.

Do bản chất chứa rất nhiều chất bên trong, và dầu cắt gọt chứa nhiều acid và amine, cũng như base thì chỉ số kiềm và acid của dầu cắt gọt sẽ thay đổi dần trong quá trình lưu trữ bởi các quá trình bay hơi của amine, các phản ứng tự oxy hoá khử và oxy hoá khử nội phân tử dẫn đến thay đổi cân bằng HLB (ưa dầu nước) bên trong tổng thể dầu cắt gọt. Khi đó dẫn đến sự chênh lệch HLB là nguyên nhân gây lắng. Dầu cắt gọt là một hệ phức tạp gồm nhiều chất bên trong, do đó chúng không bền về mặt động học và luôn có xu hướng tách pha theo thời gian (như giải thích ở trên). Khi dầu bị tách pha, thì bạn nên đổ tất cả chúng ra và khuấy đều lại và bắt đầu sử dụng bình thường. Khuyến cáo sử dụng cao hơn nồng độ thực tế 1-2% khi dầu đã tách pha.

KẾT: Việc sử dụng khúc xạ kế để kiểm tra nồng độ dầu là một trong những phương pháp đơn giản và hiệu quả để kiểm tra chất lượng của dầu cắt gọt. 

Trình bày: Steven Nguyen 

SULFURIZED EP ADDITIVE SERIES PART II - LIGHT S-EP AND ITS BASIC APPLICATION

In previous part, I have given a basic introduction of S-EP classification, dark S-EP and its application. In this part, I am going to talk about light S-EP. Because I have no right to publish TDS and MSDS without permission of suppliers, I only can show you the light S-EP which I can find them in the Internet, and these documents must belong to the big market share S-EP (i.e., DIC, ELCO, LANXESS).

I. What Is Light S-EP?

There is not a specific definition as far as I know, but I will base on DIC has shown the graph below:

Figure 1: DAILUBE Product Line

Basing on the published product line of DIC Japan and the data I have, the product with ASTM D-1500 wit a color of 6 Dil (Dilution of 15% volume) can be called light color. However, I think the S-EP with color below 8 (ASTM D-1500) without dilution should be called light S-EP. Absolutely, the color less than 5 is the perfect light S-EP.

As dark S-EP, light S-EP can be classified by its chemical structures. There are 4 typical types: light S-Olefins, light S-triglycerides, light S-Esters, and light S-Fatty acid. In general chemistry, we know that color of organic compounds depends on its saturation. The structures with more double bonds, it will become dark and dark... Therefore, to make the light color S-EP, the important process is to reduce the double bonds and chromophoric groups in its chemical structures.

2. How To Prepare Light S-Olefins EP?

RAW MATERIALS:

There are many types of raw materials to make S-EP. It can be classified as followed:

- Vegetable Oil: soybean, palm oil, tall oil...

- Animal triglycerides: lard oil, fish oil, tallow oil...

- Fatty acids, TOFA...

- Olefins: isobutane, polyisobutene...

MERCAPTAN ROUTE:

There are several ways to synthesize S-olefins EP and I will give you the brief summary on Mercaptan Route. Other is using disulfur dichloride (S2Cl2) and sodium sulfide as raw materials (you can google it for further information)

First, the reaction between H2S and olefins forms mercaptans (R-CH2-CH(SH)-R) as intermediates under Lewis acid at a widen range of temperature from -20 deg. C to 90 deg. C. Reaction temperature depends on what kinds of Lewis acids is used. 

Second, the formed mercaptans are reacted with H2O2 to form dialkyldisulfides 

2R-CH2-CH(SH)-R + H2O2 ===> R-CH2-CHR-S-S-CHR-CH2-R (1)

or dialkyl-trisulfides / dialkyl-polysulfides are synthesized through reaction of mercaptans and Sx molecules (Sulfur molecule is a cyclic octatomic molecules = S8 ring)

2R-CH2-CH(SH)-R + S2 ===> R-CH2-CHR-S-S-S-CHR-CH2-R (Dialkyl-trisulfides) + H2S (2)

2R-CH2-CH(SH)-R + Sx ===> R-CH2-CHR-S-S(x-1)-S-CHR-CH2-R (Dialkyl-polysulfides) + H2S (3)

To control the color of the reaction, high-pressure and high-temperature equipments have been employed. The reactor muse be high-pressure resistance. The operating temperature is from 120 deg. C to 170 deg. C. Pressure can be up to 50-60 bar when the olefins have low boiling point (i.e., isobutene). With high boiling olefins (e.g., diisobutene), the reaction pressure is much lower ~ 2-15 bar. By using H2S as a reducing agent, it will reduce the double bonds which are known as chromophoric groups. As a result, there are a bit double bonds in chemical structures of final products ==> the light color S-Olefins are more oxidative stable in contrast to darker ones.

Figure 2: RC 2540, Active Dialkyl-pentasulfide, Light Color

The chemical structure of RC 2540 can be described:  R-CH2-CHR-S5-CHR-CH2-R. This possesses a very light color, just type 2.5 by ASTM D-1500. Because it contains S5 in the structures, it is called active S-EP. It means it corrodes Cu and yellow alloys. As shown by ASTM D-130, it is very active just at 2.5% in base oil 3h/100 deg. C... 3b-4c... 

3. Light Color Sulfurized EP Application - Especially Metalworking Fluids

There are many applications for light color S-EP. Normally, the big consumption for S-EP is Metalworking Fluid and Grease. Others are Gear Oil, Slide-way Oils, Hydraulic Oils, Agricultural Applications, Automotive Applications.

Figure 3: EP Performance of RC 2540

The traditional Gear Oils, which can find in the Gear Oil packages of AFTON CHEMICAL and LUBRIZOL with specific smell, are Sulfured Isobutylene (SIB). SIB is often applied in the close gear box, but it cannot be used in open gear box because of its distinct odor. Future formula will be made with long-carbon chain length to avoid the bad smell due to its high boiling point.

The choose of S-EP for Bentonite Grease should be selected carefully to avoid destroying Bentonite Grease structures. Ca and Li greases can be used S-EP, but we need to pay attention on Cu corrosion protection (ASTM D-130) at specific temperature. 

If looking at the EP performance of RC 2540, there is no big difference in Welding Load when adding 2 to 15 % RC 2540. However, the scar diameter increase with an increase of its treat-rate. This can be explained by its high active sulfur... ~ 90%. Because its high activity, it dramatically reacts with metal surface to form metal sulfides leading to higher wear. Therefore, the scar diameter is directly proportional to the S content in the oil as seen in Figure 3. RC 2540 can be used to replaced SIB in many applications. It also can be used in Metalworking fluids as Lanxess recommended.

4. S-EP Manufacturers

- Arkema, France

- DIC Corporation, Japan

- Elco, US.

- Lubrizol, US.

- Lanxess, Germany.

- Others (Indian, Chinese...)

Written by Steven Nguyen

ENGINE OIL WITH API-REGISTERED MARKS: IS IT NECESSARY FOR VIETNAM MARKET?

This is just a discussion based on the writer’s opinion. Off course, there will be more and more different ones, but it is a good topic for discussion, isn’t it?

I.  A Brief of Vietnam Engine Oil Market 

 

BP Castrol has dominated Vietnam market, so the appearance of BP Castrol Engine Oil in term of color, smell, and API levels would have a big influence to the local blenders and others.  The market share of BP Castrol is around 24%.

 

Petrolimex (PLC) is the second one with a market-share of ~ 14%.  Shell, Total, Motul, Caltex and imported brands contribute 23% of total market. OEM Toyota, SYM, Suzuki, Honda, Yamaha account for 13%.  The rest belongs to Vilube, Mipec, Mekong, Nikko, Indo-Petrol, and other local brands.

 

II. Base Oil and Additive Suppliers in Vietnam

II.1. Base Oil

 

More than 10 years ago, the market used recycle oil and group I base oil to blend the engine oil. Now, they switch into mainly Group II and gradually use Group III and Group IV (PAO). I have been involved in this market since Sept. 2016, and started to see the improvements for the local blenders.

 

However, there will be the minority of the oil blended from recycle oil + solid VM to make engine oil for Mekong Delta River, Central Highlands, and Northwest Vietnam. 

 

II.2. Lubricant Additive Suppliers 

 

BIG4 and their suppliers have already been here. The latest one is Infineum, and now is distributed by Brentag.  AFTON, Lubrizol, Chevron Oronite have been here for long time.

 

Other lubricant suppliers from China, India also try to have a bit market share, but it is very hard for them. Most of the customers use those packages for low-tier products, which are cheap and competitive.

 

III. SAE Viscosity Grade

III.1. MCO

 

The majority of SAE Viscosity Grade is 10W-40, 15W-40 and 20W-50 with a widen API from SF to SN+.  However, the big market share now is API SL, and API SN could dominate in the next few years.

 

There is a trend to make a lower viscosity grade such as 10W-30, 5W-30, but I think the market of those products is not quite big at this moment. 

 

III.2. HDEO

 

SAE Viscosity Grade is 15W-40 and 20W-50 with a variety of API from CD to CI-4. Four years ago, the majority API is CF-4, but it started to switch into CI-4/SJ two year ago.  The markets for CJ-4 and CK-4 have been not started yet, even though there are some products on market and they seem to be for marketing only.

 

Market for API CD focus on the second-hand Tractors, Forklift in Mekong Delta River, and others. API CF and CF-4 are used for small trucks and passenger diesel car. API CI-4/SL are applied for container trucks and fishing boats. 

 

 IV. Are API-registered Engine Oil Suitable for Vietnam Market?

 

This part shows my opinion, it is not really correct. Just please remember. Here I would like to discuss on HDEO market because it has the biggest market for engine oil. The trucks travelling from North to South with 2-way journey will run at least 3500 Km. API CF-4 and CI-4 mineral type (Group II) recommend around 5000 - 7000 Km and 10.000 - 14.000 Km in Vietnam, respectively. Therefore, the trucks must change the oil in several rounds.

 

IV.1. Lack of National Standards for API Registered Engine Oil

 

Frankly speaking, just global company such as BP Catrol, Shell, Total, Caltex, and big local blenders in Vietnam such as Petrolimex may need to register for it. The fee of registration and extension is not cheap as well. Then, the formula with base oil and the packages should be stable. BIG4 will recommend the formula using their packages with Exxon Mobil Group II/II+ EHC base oil, and GS Caltex may be an alternative. However, GS Caltex formula has a limited formula. 

 

Vietnam government has no analytical way to identify whether any specific engine oil on markets meeting API or not. In addition, distinguishing API such as CF-4 and CI-4 is also an obstacle for the government. Vietnam government just controls the combustion engine oil based on National technical regulation on lubricating oils for Internal Combustion Engines QCVN14:2018/BKHCN. However, this just controls very basic parameters without API classification. Thus, there is no motivation for the blenders to register for API license.

 

IV.2.  Market Demand for API-registered HDEO

 

Some blenders go for API license just in the case they want to make a tender for selling other oils along with engine oils (i.e., hydraulic oil, gear oil, turbine oil). The majority of market demands also does not care for whether the HDEO has API-registered marks or not. What they need is the oil must meet their satisfactions (e.g., cheap, good quality, no soft deposit, stable VI, fuel saving).

 

Carrying overload is also an issue having a big effect on the engine oil design. Normally, many trucks in Vietnam carry overload, and some of them often drives up the mountain and down to the city. Therefore, it dramatically deteriorates the engine oil quality. Then, the truck owners will prefer the oil, which is suitable for their running condition no matter of the API license. In most cases, the manufacturers will try to enhance the lubricity and EP performance by adding small percentage Friction Modifiers (i.e., Ashless Organic FM, or Mo-DTC) and some saturated Esters (e.g., Croda 3970, Kentjenlube 135/2700). For example, when adding the FM modifier into the oil with API-registered formula, there is not guarantee that the oil will meet the API standards anymore. Then, the blenders must to choose between re-apply for API license or not. However, it is good to use for local market, why do blenders spend money on that? Once the oils meet customers’ satisfactions, there is nobody caring about the API license anymore. 

 

In summary, even though I think there is no need for the API registration for the engine oil, the local blenders should use BIG4 additive package to make the high quality and long-lasting performance for Vietnamese people. 

 

Written by Steven Nguyen.

 

SULFURIZED EP ADDITIVE SERIES PART I - DARK S-EP FOR METALWORKING FLUIDS

I. DIFFERENCE BETWEEN EP AND AW ADDITIVE

Extreme Pressure (EP) and Anti Wear (AW) additives are very common in metalworking fluids (MWF) industry. The classification of those additive are very confused for those who is just involved in this industry as I used to be 4 years ago. However, I will not talk about their lubricity mechanism, so I will distinguish them very short and easy to understand as follow.

- AW become effective at relatively low contact temperatures and become ineffective at moderate contact temperatures. Four-ball Test ASTM D 4172 (lubricating fluids) can be used to check the scar diameter at 1200 rpm in 60 mins with a force of ~ 40 Kg, 1/2 inch steel balls. Some products can be run up to 98 Kg, even more.

- EP additive remains its effective at relatively high contact temperatures. Four-ball Test ASTM D 2783, 1,770 rpm, RT, 10 sec, 1/2-inch steel balls. Welding load and Last Non-Seizure Load (LNSL) are the key important parameters in this test.

As you can see in the Fig. 1, A to B is "ball to ball" contact, B to C to D is "face to face" contact. 

- AW will affect B point, when formulators can accept metal shape change, they will expand the B point by adding more AW additive.

Figure 2: Real test data of ADEKA Additive for AW/EP test.

- EP additive will enhance the D point. If lubricant-makers want to continue machining even though the metal shape change happens.

II. SULFURIZED EP ADDITIVE

- There are 4 typical types of S-EP additive based on their chemical structure: S-olefin, S-triglyceride, S-ester, S-fatty acid. Some manufacturers can make a mixture containing more than 2 of those types to enhance the EP performance.

Figure 3: Sulfurized Olefin

Figure 4: Sulfurized Ester

Figure 5: Sulfurized Triglyceride (Dark Sulfur)

Figure 6: Sulfurized fatty oil/olefin mixture (light color).

- In term of their color, EP additive can be classified into 2 types: Dark and Light colors.

- Some people will pay attention to its activity, so there are Active and Inactive S-EP additives. Some manufacturers distinguish those 2 types based on the Sulfur chain in the chemical structure. Inactive is less than 3 Sulfur, and Active is from 4 to 5 Sulfur. Others will pay attention to the result of ASTM D-130 and ASTM D-1662.

Figure 7: Properties of S-EP additives

The very basic properties of S-EP can be shown in the Fig. 7. Those are just very basic information, the key important thing is how you formulate the oil for machining, and the majority of the blenders around the world are not afford to buy a four-ball machine. Therefore, you need to understand the machining process and chemical structures of additives to take advantage of the synergistic effect of them for the optimized products for real test in your customers workshops.

III. DARK SULFURIZED EP ADDITIVE AND ITS APPLICATION

In principle, the molecules contains many chromophoric functional groups will enhance the color intensity; therefore, the colors will be darker. As you can see in Fig. 5, Dark S-EP always contains the chromophoric groups in its chemical structure. These structure are not chemically stable since its activity is very high.

The S-EP is the cheapest ones in S-EP additive because of the available raw materials and its less complicated synthesis process. There are 3 types of dark S-EP: S-olefin, S-ester, and S-triglyceride (vegetable or lard oil). You can see the basic classification of DIC S-EP products in Figure 8.

Figure 8: Classification of DIC S-EP Additive

Dark S-EP additives normally are applied in the low-tier cutting and forming applications where the customers can accept its smell and dark colors with a reasonable price and medium performance. 

HERE ARE SOME BASIC PROPERTIES OF THE DARK S-EP:

- Anti-oxidant (AO): Dark S-EP has lower anti-oxidant performance because there are many unsaturated groups in the structure shown in Fig. 7. Light-colored products manufactured with high-pressure hydrogen sulfide processes or by mercaptan oxidation, so it does not maintained the unsaturated double bonds left in the structures ==> they show better oxidation stability.

- Lubricity: Please take a look at Fig. 7. Sulfurized triglyceride provide the best lubricity in both inactive and active type, the second one is ester, and the last one is S-olefin. Lubricity depends on its chemical type. There is nothing to deal with dark and light color. However, at the same chemical structure, the higher MW of dark S-EP may provide the better EP/AW performance.

- Polymerization: Triglyceride type (i.e., lard oil, soybean oil) do polymerize and form solid (e.g., rubberlike products). Because olefins consist of few double bonds and some process can reduce the structure to make only one double bond structure, the polymerization can be controlled. Esters are quite similar to olefins, but due to its natural chemical structure varying amounts of multiple unsaturated compounds, polymerization also can take place. Dark S-EP products will also resume polymerization after the production process is finished.

- Solubility and Polarity: The more polarity, the less solubility in oil. S-EP solubility > S-Ester > S-triglyceride.

- Storage stability: Depending on the raw materials, its chemical structures, and sulfurization process plus technique, some S-EP will continue to polymerize during storage, especially dark S-EP triglyceride type.

Watching Part II: https://phugiadaunhot.blogspot.com/2020/10/sulfurized-ep-additive-series-part-ii.html

Written by Steven Nguyen. 

ELECTROSPRAY - DIFERENTIAL MOBILITY ANALYSIS (ES-DMA): A BASIC INTRODUCTION FOR COLLOIDAL NANOPARTICLES CHARACTERIZATION

 1. WHAT IS ES-DMA?

ES-DMA is an analytical technique that uses an electrospray to aerosolize nanoparticles before characterizing their electrical mobility by DMA at ambient conditions. Quantitative characterization of bio-macromolecules and nanoparticles from 10 to hundreds nm can be achieved by ES-DMA.

 

Figure 1: Schematic of ES-DME system. (D-H. Tsai, R. A. Zangmeister, L. F. Pease III, M. J. Tarlov, and M. R. Zachariah Langmuir 2008 24 (16), 8483-8490)

As shown in FIGURE 1, ES-DMA consists of an ES generator, a differential mobility analyzer column, and a condensation particle counter. The ES generator aerosolizes nanoparticles through a nozzle 

 

First of all, the nanoparticle dispersion is added to a volatile buffer and placed inside a pressure chamber. Second, the solution is delivered to the nozzle through a capillary to aerosolize multiply charged droplets. Then, the droplets are mixed with air and carbon dioxide before passing through the neutralizer. After that, the solvent is evaporated and there is a decrease in the droplets charge distribution. As a result, more and more droplets contain single net charge nanoparticles which continue to pass through the DMA. DMA separates positively or negatively charged particles by applying a negative or positive potential. Inside a DMA is a complicated process, but I will try to explain it shortly. DMA will exist in an electric field to collect the charged particles based on their electrical mobility, the fluid flow rate, and the DMA geometry. Therefore, the electrical mobility of particles will be identified by DMA. By applying Stoke's law, the particle diameter can be calculated. To identify the number concentration of the size-selected particles, the CPC is used.

 

 

Figure 2: Condensation Particle Counter (CPC) Working Principle. (Suvajyoti Guha, Mingdong Li, Michael J. Tarlovand Michael R. Zachariah -Trends in Biotechnology May 2012, Vol. 30, No. 5)

 

2. Which information can be provided through ES-DMA?

- Mobility Diameter and Number concentration per unit volume (as shown in Figure 3).

- Kinetic Stability of polymeric conjugated-particles in different pH can be also observed through Mobility Diameter Distribution Change (as shown in Figure 3).

Figure 3: BSA-AgNPs. (a) Particle size distributions of BSA-AgNPs at pH 6.7 measured by ES-DMA. (b) Particle size distributions of BSA-AgNPs at pH 2.7 measured by ES-DMA. (c) Particle size distributions of BSA-AgNPs at pH 2.3 measured by ES-DMA. (d) TEM analysis of monomers and finite-sized clusters of BSA-AgNPs. Samples were at pH 2.5. CBSA= 2 μmol/L. The scale bars were 20 nm.(Jui-Ting Tai, Chao-Shun Lai, Hsin-Chia Ho,  Yu-Shan Yeh, Hsiao-Fang Wang, Rong-Ming Ho,and De-Hao Tsai - Langmuir . 2014 Nov 4;30 (43):12755-64)

- Aerosol particle mass analyzer (APM) coupled with ES-DMA can provide Mobility Diameter + Number concentration + Particle Mass.

Figure 4: Cartoon depiction of electrostatic-directed assembly of GO with surface functionalized AgNPs (Step 1), characterization of GO-AgNP aqueous colloid using a stand-alone ES-DMA (Step 2), and a coupled instrument, ES-DMA/APM (Thai Phuong Nguyen, Wei-Chang Chang, Yen-Chih Lai, Ta-Chih Hsiao & De-Hao Tsai  - Analytical and Bioanalytical Chemistry, 409,5933–5941, 2017)

HLB VALUE - A KEY FOR SELECTION OF EMULSIFIER SYSTEM IN METALWORKING FLUIDS IN COLLOID AND INTERFCE SCIENC POINT OF VIEW.

1. WHAT IS HLB?

 

The abbreviation HLB stands for “Hydrophile-Lipophile Balance”, this is a strong value for formulators to select the right HLB system for their basis of MWF design.

 

When I mention HLB value in this topic, I want to talk about the non-ionic surfactant. Anionic surfactant and zwitterionic surfactants can be discussed in the formulation.

 

2. HLB VERSUS SOLUBILITY OF EMULSIFIERS.

 

The HLB value of an emulsifier reflects its solubility. Low HLB value surfactant can be called oil-soluble, and a higher one tends to be water-soluble. Noting that: some emulsifiers may have the same HLB value, but it shows a difference in solubility and its behaviors.

 

When we work on emulsifiers and surfactant systems, we will be soon know the correlation between its solubility and behavior in solution (maybe water or oil).

 

TABLE 1: CORRELATION BETWEEN HLB VALUE AND ITS USE

TABLE 1 has shown the application of emulsifiers based on their HLB value. This is very basic knowledge, but it may go not well when you start to apply them to design the MWF system. 

 

                   

3. REQUIRED HLB (rHLB) VALUE OF OIL

 

Simply said: each type of oil requires a specific HLB value of an emulsifier or emulsifier system to be emulsified. It means the required HLB of the oil needs to be the same as the HLB value of emulsifiers to make a kinetically stable emulsion. (rHLB ~ HLB). Normally the rHLB of mineral oil is from 9 to 11 (+/- 1) for O/W emulsion, but it will become 6 +/- 1 for W/O emulsion. 

 

TABLE 2: rHLB VALUE OF OIL FOR O/W AND W/O EMULSION

 

 

rHLB calculation of oil systems contains many ingredients inside will be the same method as HLB calculation. rHLB of each oil = weight portion of emulsifier x its rHLB. rHLB of system = total rHLB of each composition inside. 

 

For example, if you are making an O/W emulsion textile lubricant. The product might be

30% mineral spirits, 50% cottonseed oil, and 20% chlorinated paraffin to be emulsified in water. The required HLB of the combination can be calculated as follows:

Mineral Spirits ..........30% X Req. HLB 14 = 4.2

Cottonseed Oil ..........50% X Req. HLB 6 = 3.0

Chlorinated Paraffin . . 20% X Req. HLB 14 = 2.8

==> rHLB = 4.2 + 3.0 + 2.8 = 10.0, then we must go with the HLB value 10 +/- 1.

 

However, what if we use some oil that does not have the rHLB value in the above table? Then, we need to run some experiments to determine rHLB of the oil.

 

4. DETERMICATION OF rHLB FOR UNKNOWN OIL

 

No matter if you can find the rHLB of your oil in TABLE 2, it is much better to identify the right rHLB of the oil through experimental determination because oils and waxs from different manufacturers will have different properties and rHLB value. THIS IS ALSO TRUE FOR EMULSIFIERS. DIFFERENT MANUFACTURERS WILL SHOW SLIGHTLY DIFFERENT HLB VALUE.

 

To run the test, we need to select a pair of emulsifiers. It is highly recommended to select the same chemical structure of emulsifiers. For example, “80” SPAN-TWEEN emulsifiers are both oleate esters. It can be used to make a HLB system with a value from 4.3 (Span 80) and 15 (Tween 80). This also my experiments have done before with Base Oil 150N (FORMOSA Taiwan) before, to identify the rHLB value of this 150N Base Oil.

                             TABLE 3: CALCULATION HLB VALUE OF “80” SPAN-TWEEN

 

      

Sample No.	Emulsifiers		Calculated HLB
	4.3	15
	Span 80	Tween 80
1	100	0	4.3
2	90	10	5.37
3	80	20	6.44
4	70	30	7.51
5	60	40	8.58
6	50	50	9.65
7	40	60	10.72
8	30	70	11.79
9	20	80	12.86
10	10	90	13.93
11	0	100	15

For example: Emulsifier systems contain 60 wt.% of Span 80 and 40 wt.% of Tween 80 ==> HLB value of system = (60*4.3 + 40*15.0)/100 = 8.58

 

 

 My experiments 

 

Before running the emulsion test, I ran the solubility test to identify the solubility of 11 emulsifiers system in TABLE 3 with different Calculated HLB values. 11 samples will be added into oil, and the other 11 samples will be added into water. Then, taking note of its solubility. The amount of emulsifier can be equal to 10-20% of the oil. They’re 3 situations may happen:

- HLB < 8 will be oil soluble.

- HLB > 10 will be water-soluble.

- HLB ~ 8-10 can be solubilized in both oil and water. 

 

After that, I ran the emulsion test for 11 samples. Here I chose 1 gram emulsifiers + 4 grams 150N Base Oil + 95 grams water (equal to 5% soluble oil after dilution). The emulsifiers system with HLB less than 10.0, I will mix them with base oil first, and then pour them into water. However, those with HLB value higher than 10.0, I will add them into the water before pouring oil inside. After that, the mixture will be shaken several times, and leave it 24 hours. I found that the emulsifier system has HLB from 8-10 shows very good emulsion stability without creaming or oil separation after 24 hours. This is a very quick method to identify the rHLB value of 150N base oil in my experiment. Then, I go further with the HLB value of 0.5 units apart in the range from 8 to 10. (8.0; 8.5; 9.0; 9.5; 10.0), and observe the emulsion kinetic stability after 10 days. Then, I found that the HLB value of 9.0 is quite stable, it means the rHLB of 150N base oil in my experiment is ~ 9.0.

 

 

However, even though the rHLB value of 150N base oil has already identified, you still face a problem when using the different chemical structures of emulsifiers with the same HLB value to emulsify 150N base oil at the same treat-rate. In some cases, you need to use a higher or lower treat-rate than that of the experimented data when using the different emulsifier systems. If you understand Colloid and Interface Science, you can explain what is going on.

 

5. COLLOID AND INTERFACE SCIENCE IN METALWORKING FLUIDS

5.1. Mole

What is a mole? 1 mole = 6.02214076×10²³ particles, ions, atoms, molecules, electrons…

 

In chemistry, the mole is a very important parameter to calculate the mass transfer in a chemical reaction. When we work with different emulsifiers have the same HLB value with different molecular weight (MW) and both of them do not have any amine/amide or basic functional groups in the structures. At 1 gram of selected emulsifier, the lower MW emulsifier has a bigger number of molecules. Assumption, 2 emulsifiers produce the same mean diameter emulsion, it means lower MW has more chance to reach maximum coverage. It may cause better surface protection and emulsion stability than the higher MW emulsifier.

 

2. pH and Zeta potential

 

pH and Zeta potential are effective factors to identify the kinetic stability of the emulsion. If we choose amide emulsifiers vs. Span-Tween systems with the same HLB value, the amide system may show better emulsion stability due to electrostatic repulsion of the electrical double layer, especially Zeta potential value. 

Zeta potential of colloid (emulsion) behaves as a function of pH. The higher the pH, the better the zeta potential. It means the emulsion will be more stable. In some cases, Zeta potential starts with a positive surface charge at acidic pH and it becomes a negative surface charge at basic pH. There will be an isoelectric point (IEP), where the surface charge is zero. At this IEP, the emulsion will immediately separate into 2 phases: Oil and water. As far as I know, the IEP does not exist in water-based metalworking fluids. This is because the main emulsifiers in this fields are anionic and non-ionic with a few amounts of amide types. Therefore, the MWF emulsions should be negatively charged at all the pH. We can run the zeta potential test to ensure the results if your factory has the zeta sizer machine to run DLS and zeta potential. 

There will be another parameter I have not mentioned yet is the degradation of the non-ionic surfactants which have esters, ether, amide functional groups. These groups may be hydrolyzed in the strong basic pH causing the instability of emulsion.

 

3. Molecular weight of emulsifiers.

 

Steric repulsion beside electrostatic repulsion also plays an important role to check the stability. This may happen when using the big molecular emulsifiers (polymeric emulsifiers), such as PIBSA, in the formula. 

 

To observe this effect, you may find some MWF packages using PIBSA technology from ITALMATCH. However, the combination of PIBSA + Sodium Petroleum Sulfonate + Non-ionic surfactants (Amide types) can bring very good finished emulsion in terms of cost, kinetic stability, corrosion protection. The formulator can protect the emulsion with 2 emulsion stability mechanisms: electrostatic repulsion and steric repulsion.

 

4. Water quality

 

Hard water can destroy the emulsion using anionic surfactants, but it can be handled by using the non-ionic and polymeric surfactants. Anionic surfactants will react with Mg2+ and Ca2+ to form the Lime soap as the picture below. Therefore, by using non-ionic surfactants or the combination of non-ionic and anionic surfactants can make the emulsion with high water hardness tolerance. 

 

Written by Steven Nguyen