The Role of Silicone Surfactants as Surface Tension Reducing Agents in Polyurethane Foam

Transcription

1 The Role of licone Surfactants as Surface Tension Reducing Agents in Polyurethane Foam 硅油表面活性剂在聚氨酯发泡中所扮演的角色 Presented by: Masao Takase 高濑正男 Dow Corning Toray Co., Ltd. Translated by: KH Boo 巫光珂

2 Today s presentation 主要内容 Component roles in the foaming process Structure of silicone surfactants Four roles of a silicone surfactant Emulsification improving compatibility of raw materials Nucleation of bubbles Prevention of coalescence (slow-down of diffusion) Stabilization Attributes important to surfactant selection Conclusions 2

3 Component roles in the foaming process 各个组分在发泡中的作用 Polyol Isocyanate Water Amine Catalyst Tin Catalyst Blowing Agent Surfactant Chemical reaction: Chain extension Gas formation Crosslink Control of physical phenomena: Static surface tension Dynamic surface tension Interfacial tension Polymer PU Foam Cell 3

4 Types of structures 结构类型 ABA Type Branch Type (AB) n Type loxane Unit Rake Type / Pendant Type Polyether Unit 4

5 Surface tension of raw materials 各个原料的表面张力 Surface Tension w ith and w ithout licone Surfactant 70 Surface Tension (mn/m) Without Surfactant With Surfactant 0 Water + NEM(0.1%) TDI-80 PPG(Mw =3000) Blow ing Agent Entire Sytstem Surface tension of silicone surfactant: 21.4[mN/m]; concentration of silicone surfactant: 1.0pphp. 5

6 The four roles of a silicone surfactant 硅油表面活性剂的四个主要作用 Control of Interfacial Phenomenon Support of mixing Stabilization of bubbles 1. Improved compatibility of raw materials 3. Prevention of coalescence 2. Dispersion of inlet gas 4. Stabilization of bubbles Mixing to cream time Liquid Cell is not formed Cream time to gel time Gel Polymer Cells are formed 6

7 1. Improving compatibility of raw materials 改善原料相容性 The silicone backbone will drive toward hydrophobic/nonpolar materials. The surfactant acts at the interfaces of the formulation components. Polyether pendants can be designed to be soluble in different polar components of the system. Depending on the specific system, it is possible for the silicone polyether to improve the compatibility between materials. 7

8 2. Nucleation 成核 Many factors affect the rate of nucleation and bubble growth in the system. It has been shown, in theory and in practice, that lowering the surface tension of the system leads to an increased number of fine cells in the foam. 8

9 2. Nucleation - Dispersion of inlet gas 气体成核 Less surfactant can lead to a higher surface tension, which can cause coarse cells. 1 Part licone Surfactant 0.3 Parts licone Surfactant 9

10 2. Nucleation of stable bubbles 稳定泡沫成核 According to classical nucleation theory, for a stable bubble to form, there has to be enough Gibb s free energy to reach a critical radius/nucleus. (1) Gibb's FreeEnergy of 16 *surfacetension forminga criticalradius = π 2 3 P This equation shows that lowering the surface tension also lowers the amount of energy needed for nucleation! 10

11 No Surfactant 1% Surfactant Number of bubbles increased ze of bubbles decreased Carbonated Soda Shaken for 3 Seconds

12 The four roles of a silicone surfactant 硅油表面活性剂的四个主要作用 Control of Interfacial Phenomenon Support of mixing Stabilization of bubbles 1. Improved compatibility of raw materials 3. Prevention of coalescence 2. Dispersion of inlet gas 4. Stabilization of bubbles Mixing to cream time Liquid Cell is not formed Cream time to gel time Gel Polymer Cells are formed 12

13 3. Prevention of coalescence 防止泡沫结合 (slowing down diffusion) Gas will diffuse from areas of high pressure to areas of low pressure. Therefore, gas will flow from smaller bubbles into larger bubbles. LaPlace and Young theorized the following: 2*Surface Tension * 1 radius 1 gas(1) gas( 2 ) (1) radius (2) = P P = P The rate at which the gas diffusion takes place is proportional to P. (2) Therefore, decreasing the surface tension decreases P, which decreases the diffusion rate. 13

14 3. Prevention of coalescence (slowing down diffusion) Example of coalescence! Higher Pressure Lower Pressure Higher Pressure PPB Lower 1 1 P = 2λ rb ra λ = r Pressure PB Larger Pressure Drop Smaller Pressure Drop Both are very stable foams.

15 4. Stabilization 稳定泡沫作用 There are many theories as to how a surfactant helps stabilize a foam: Gibbs Marangoni Ewers & Sutherland Plateau We will highlight a few. 15

16 Marangoni effect on stabilization: Fluid flows from low surface tension to high. Higher-tension area created Liquid flow pushes fluid back to stabilize the thinned wall. 16

17 4. Stabilization by Surfactant Migration 表面活性剂迁移所产生的稳定性 Surfactant will flow from an area of high to low concentration! This will not only drop the surface tension of the newly formed area, but it also will drag with it some of the entangled liquid layer (theorized by Ewers/ Sutherland). (2)

18 Does surface tension control everything? 表面张力是否控制一切? No, it does not. Other important variables that impact performance and surfactant selection: Solubility characteristics Molecular weight differences Reactivity differences etc. 18

19 Surface tension is only one of the many variables! This foam completely collapsed in seconds with an ultra-low surface tension surfactant! Surfactant 21 Dynes/cm Surfactant 30 Dynes/cm 19

20 Important roles of silicone surfactant by application 硅油表面活性剂的功能要求 Flexible Slab HR Molded Rigid Improving Raw Material Compatibility Medium Medium High Dispersion of Inlet Gas Medium Medium High Prevention of Coalescence Medium Medium Medium Stabilization High Low Medium 20

21 Structural components of silicone surfactant 硅油表面活性剂结构组成 1. Type of structure 2. loxane Mw 3. Modified polyether Mw 4. Number of modified polyether unit 5. EO / PO ratio of polyether 6. End unit of polyether 7. Copolymer Mw 8. licone content of copolymer O O O m n C 3 H 6 O(EO) a (PO) b R 21

22 Flexible slab and hot mold 软质大块泡沫及热模塑高回弹泡沫 O O O m n C 3 H 6 O(EO) a (PO) b R High Mw of siloxane and polyether O-R capped polyether EO/PO ratio of polyether is approximately 50 to 50 licone content of copolymer is lower 22

23 HR mold 高回弹模塑泡沫 O O O m n C 3 H 6 O(EO) a (PO) b R Low Mw of siloxane and polyether Various kinds of polyether licone content is wide range 23

24 Rigid refrigerator/construction 硬泡 冰箱 / 建筑材料 O O O m n C 3 H 6 O(EO) a (PO) b R Medium Mw of siloxane and polyether High EO content of polyether 24

25 Conclusions 总结 Physical phenomena such as Emulsification, Nucleation of bubbles, Prevention of coalescence, and Stabilization are significantly influenced by the selection of the silicone surfactants. Selection of the right surfactant is a key to your success! Dow Corning knows which is the ideal molecule to help you meet the requirements of your system. For more information: Please visit the Dow Corning booth #818 Visit our website, Or us at specialtychemicals@dowcorning.com 25

26 References 参考文献 1. Lee, S.T., & Ramesh, N.S. (2004). Polymeric Foams: Mechanisms and Materials, p 81. New York: CRC Press LLC. 2. Herrington, Ron, & Hock, Kathy. (1997). Dow Polyurethanes: Flexible Foams, p 3.12 and USA: The Dow Chemical Company. 26

27 Some of your Dow Corning polyurethane foam team DC PUA 团队 Bee Yung, Chris Velasquez Vicky James, Masao Takase, Stephanie Gathman Kuang Hoe "KH" Boo