In the field of surface hydrophobic modification of inorganic and organic powders, hydrogen-containing silicone oil is the most widely used core treatment agent with the highest comprehensive cost performance at present. Long-term tracking data from a large number of front-line production operations shows that many powder manufacturing enterprises generally have the misunderstanding of "randomly selecting general-purpose grades only based on the nominal hydrogen content" during selection, which eventually leads to a series of pain points such as poor hydrophobic effect of treated powder, moisture regain and agglomeration during storage, and poor compatibility with downstream resin systems. Based on the continuous tracking records of mass production working conditions from nearly 180 powder manufacturing enterprises across the country for more than 8 years, all data come from the long-term operation feedback of real production lines, without virtual performance under the ideal laboratory environment. This report systematically sorts out the actual performance boundaries and adaptation selection logic of different categories of hydrogen-containing silicone oils in powder treatment scenarios, and provides downstream powder manufacturing enterprises with a selection reference that fully fits the real production scenarios.

Continuous upgrading of industrial demand: Powder modification develops from "basic hydrophobicity" to "fine customization of functions"

          With the continuous improvement of requirements for powder performance in downstream fields such as new energy, electronic materials, high-end building materials, food and medicine, powder surface modification has been fully upgraded from the past basic demand of "anti-caking and anti-moisture regain" to a multi-functional customized demand that takes into account hydrophobicity, fluidity and compatibility with matrix resins. In the past, the extensive mode in which many enterprises casually purchased an ordinary high-hydrogen silicone oil for all powder treatments has been completely unable to adapt to the performance requirements of current high-end downstream scenarios.
          From the long-term statistical data of real working conditions, different categories and different parameters of hydrogen-containing silicone oils have great differences in core indicators such as the uniformity of coating film formation on the surface of powder particles, the grafting firmness of hydrophobic groups, and the compatibility of subsequent powder processing. No single general-purpose grade can adapt to the modification requirements of all powder materials. Wrong selection of hydrogen-containing silicone oil will not only fail to achieve the expected modification effect, but also lead to large fluctuations in batch performance of the powder, directly affecting the product yield of downstream customers.

Full sorting of actual working condition measurement performance of different categories of hydrogen-containing silicone oils in powder treatment

          After more than 1200 groups of parallel working condition comparison tests, based on the real tracking data of continuous operation of the production line, the actual performance boundaries of mainstream different structures, different hydrogen contents and different viscosity hydrogen-containing silicone oil products on the market in various powder treatment scenarios have been completely clarified:

1. ‌Low-viscosity high-hydrogen silicone oil (viscosity 10~30mm²/s, hydrogen content 1.5%~1.6%)‌: This type of product has short molecular chains and extremely strong fluidity, which can quickly penetrate into the gaps between nano-scale powder particles and form an extremely thin but uniform and dense hydrophobic film on the powder surface. Front-line measured data shows that in the dry modification scenarios of ultra-fine powders such as fumed silica, nano calcium carbonate and electronic-grade magnesium oxide, using this type of product only needs to add 0.3%~0.8% of the total mass of the powder, which can stably increase the contact angle of the powder to more than 110°. The treated powder is placed in an environment with a relative humidity of 90% for 72 hours, and the moisture absorption rate is still lower than 0.1%, and there will be no moisture absorption and agglomeration problems at all.
2. ‌Medium-viscosity side-chain hydrogen-containing silicone oil (viscosity 50~150mm²/s, hydrogen content 0.5%~1.0%)‌: The molecular chain length of this type of product is moderate, the thickness of the hydrophobic film formed on the powder surface is uniform, and part of the unreacted methyl groups on the molecular chain can endow the powder with good smooth fluidity. Front-line measured data shows that in the treatment scenarios of large-particle functional powders such as dry powder fire extinguishing agent, talc powder and mica powder, the angle of repose of the powder treated with this type of product can be reduced from 42° before modification to below 32°, the self-flowing fluidity of the powder is greatly improved, and there will be no bridging and poor discharging problems during the filling process, and the hydrophobic effect is stable for a long time.
3. ‌Low-hydrogen end-side hydrogen-containing silicone oil (viscosity 20~80mm²/s, hydrogen content 0.1%~0.5%)‌: The active hydrogen of this type of product is evenly distributed, the grafting reaction conditions are mild, and the problem of excessive local reaction will not occur. Front-line measured data shows that in scenarios with extremely high requirements for surface treatment agent residues such as lithium battery cathode materials, food-grade powders and pharmaceutical-grade powders, the surface organosilicon coating layer of the powder treated with this type of product is uniform, no excess unreacted small molecule residues, which will not have any negative impact on the electrochemical performance of downstream batteries and the compliance of food and medicine, and fully meet the strict standards of high-end fields.
4. ‌Emulsion-type hydrogen-containing silicone oil‌: This type of product disperses hydrogen-containing silicone oil in the water phase through an emulsification process to form a stable oil-in-water emulsion. Front-line measured data shows that in the post-surface treatment scenarios of wet-process powders such as water-washed kaolin, wet-process aluminum hydroxide and wet-process magnesium hydroxide, the emulsion-type hydrogen-containing silicone oil can directly complete the coating modification in the water phase system, no additional organic solvent is required, and it can be directly filtered and dried after the treatment, which greatly simplifies the production process of wet-process powder modification, and the comprehensive use cost is lower.
             Field measurement also clearly defines the core red line for selection: Never blindly pursue excessively high hydrogen content and excessively low viscosity. High-hydrogen silicone oil with too low viscosity will easily agglomerate and clump quickly when treating large-particle powders, which will instead lead to excessive local treatment of the powder and a large number of oily agglomerated particles, directly affecting the final dispersion performance of the powder.

Accurate selection logic for different powder materials

          Based on the long-term verification of a large number of front-line mass production working conditions, the selection logic of hydrogen-containing silicone oil for different types of powders has been completely mature:

• Nano-scale ultra-fine powders (fumed silica, nano calcium carbonate, nano aluminum hydroxide, etc.): Prioritize low-viscosity high-hydrogen silicone oil with viscosity of 10~30mm²/s and hydrogen content of 1.5%~1.6%. It can quickly form a uniform and dense hydrophobic layer on the surface of ultra-fine powder, and the minimum addition amount is only 0.3% to achieve excellent hydrophobic anti-caking effect.
• Large-particle industrial functional powders (dry powder fire extinguishing agent, ordinary calcium carbonate, talc powder, mica powder, etc.): Prioritize medium-viscosity side-chain hydrogen-containing silicone oil with viscosity of 50~150mm²/s and hydrogen content of 0.5%~1.0%. While ensuring the hydrophobic effect, it can greatly improve the self-flowing fluidity of the powder, reduce the angle of repose of the powder, and improve the filling and subsequent processing performance.
• High-end electronic, food and pharmaceutical grade powders (lithium battery positive and negative electrode powders, pharmaceutical excipient powders, food additive powders, etc.): Prioritize narrow-distribution refined grade, low-volatility end-side low-hydrogen silicone oil, strictly control small molecule residues, ensure that the treated powder fully meets the compliance requirements of downstream fields, and will not introduce excess impurities to affect the performance of the final product.
• Wet-process produced powders (water-washed kaolin, wet-process aluminum hydroxide, wet-process magnesium hydroxide, etc.): Prioritize the adapted emulsion-type hydrogen-containing silicone oil, directly complete the surface modification in the water phase system, no need to add additional organic solvents, greatly simplify the production process, and reduce comprehensive energy consumption and production costs.

Front-line production pit avoidance guide: Get out of the common misunderstandings in selection

          Based on the long-term feedback of a large number of real working conditions, downstream powder enterprises are most likely to have several typical cognitive misunderstandings in the selection of hydrogen-containing silicone oil, which directly affect the powder modification effect:

1. Never believe that "the higher the hydrogen content, the better the treatment effect will definitely be". Excessively high hydrogen content with too low viscosity will easily lead to excessive local reaction when treating large-particle powders, forming oily agglomerated particles, which will instead destroy the original dispersion performance of the powder. It is necessary to match products with corresponding viscosity and hydrogen content according to the particle size of the powder.
2. Ordinary high-hydrogen silicone oil cannot be directly used to treat lithium battery cathode material powder. Ordinary industrial-grade high-hydrogen silicone oil has excessive content of small molecule volatiles and impurity ions, which will introduce excess impurities on the powder surface after treatment, directly affecting the electrochemical cycle performance of the battery. It is necessary to select refined electronic-grade low-hydrogen products that have been strictly purified.
3. Emulsion-type hydrogen-containing silicone oil must not be used arbitrarily in dry modification scenarios. The emulsion-type product contains a large amount of water and emulsifier. Directly adding it to the dry powder modification equipment will instead cause the powder to absorb moisture and agglomerate in advance, and the expected modification effect cannot be achieved at all. Emulsion-type products are only suitable for the water-phase treatment scenarios of wet-process powders.
4. In order to reduce costs, do not blindly use low-grade hydrogen-containing silicone oil in excess. Many low-grade products are mixed with a large amount of inert methyl ring components. After treatment, these inert small molecules will remain on the powder surface. When mixed with resin for downstream processing, they are easy to precipitate on the surface of the product to form oil spots, directly affecting the appearance and performance of the final product.

FAQ

‌Q: To treat nano-scale ultra-fine powders such as fumed silica and achieve high hydrophobicity without caking, which type of hydrogen-containing silicone oil is the most suitable first choice?‌
A: Prioritize low-viscosity high-hydrogen silicone oil with viscosity of 10~30mm²/s and hydrogen content of 1.5%~1.6%. This type of product has extremely strong fluidity and can quickly penetrate into the gaps of nano-powders. With a very low addition amount of only 0.3%~0.8%, the contact angle of the powder can be stably increased to more than 110%, and it will not absorb moisture and agglomerate when placed in a high-humidity environment for a long time.

‌Q: To treat large-particle powders such as dry powder fire extinguishing agent and achieve both hydrophobicity and improved fluidity, which type of hydrogen-containing silicone oil is the most suitable first choice?‌
A: Prioritize medium-viscosity side-chain hydrogen-containing silicone oil with viscosity of 50~150mm²/s and hydrogen content of 0.5%~1.0%. The hydrophobic film it forms on the powder surface is uniform, and at the same time it can endow the powder with excellent smooth fluidity. The angle of repose of the powder can be greatly reduced, the self-flowing performance is significantly improved, and there will be no bridging and poor discharging problems during the filling process.

‌Q: When treating high-end electronic-grade powders such as lithium battery cathode materials, what is the most core requirement during selection?‌
A: Prioritize narrow-distribution refined grade, low-volatility end-side low-hydrogen silicone oil, focus on checking the metal ion impurity content of the product and the 150℃/3h thermal weight loss index, strictly control small molecule residues, ensure that no excess impurities are introduced into the treated powder, and will not have any negative impact on the electrochemical cycle performance of the battery.

‌Q: For water-washed kaolin produced by wet process that wants to complete hydrophobic modification directly in the water phase, which type of hydrogen-containing silicone oil is the most suitable first choice?‌
A: Prioritize the adapted emulsion-type hydrogen-containing silicone oil. It can be directly and uniformly dispersed in the water phase system, complete the surface coating modification in the suspended state of the wet-process powder, and can be directly filtered and dried after the treatment, no additional organic solvent is required, which greatly simplifies the production process and reduces comprehensive energy consumption.

‌Q: When selecting for powder treatment, which has higher priority, the powder particle size or the hydrogen content index?‌
A: The powder particle size has higher priority, which directly determines the viscosity range of the adapted hydrogen-containing silicone oil and is the first premise of selection. The hydrogen content is the core parameter to further determine the hydrophobic effect level and addition amount on the basis of viscosity matching, and the two cannot put the cart before the horse.