WO2020186579A1

WO2020186579A1 - Preparation method for environmentally friendly super-hydrophobic coating with high mechanical durability

Info

Publication number: WO2020186579A1
Application number: PCT/CN2019/082159
Authority: WO
Inventors: 苗徳俊; 程英模; 蒋家琛; 孔令晓; 徐毓名
Original assignee: 山东科技大学
Priority date: 2019-03-19
Filing date: 2019-04-11
Publication date: 2020-09-24
Also published as: CN109943213B; CN109943213A

Abstract

A preparation method for an environmentally friendly super-hydrophobic coating with high mechanical durability, comprising the following steps: using filtered and purified waste edible oil as a raw material, synthesising the waste edible oil fatty amides by means of an amino decomposition reaction; using waste edible oil fatty amides and toluene diisocyanate as raw materials, employing a one-step process to prepare a polyurethane prepolymer; capping the polyurethane polymer by means of a double-ended ammonia-based silicone oil to obtain modified polyurethane; mixing the silicone-modified polyurethane with hydrophobically treated silicon carbide particles and, after magnetic stirring, spraying same onto a substrate, and drying and curing to obtain the super-hydrophobic coating.

Description

Preparation method of environment-friendly super-hydrophobic coating with high mechanical durability

Technical field

The invention relates to the technical field of coating preparation, in particular to a preparation method of an environmentally friendly superhydrophobic coating.

Background technique

Due to long-term mining, shallow coal seams have been exhausted, and most coal mines have to mine deep coal seams. As the mining depth increases, the temperature of the surrounding rock also rises, leading to an increasing risk of thermal damage in mining operations. For high temperature mines, under normal circumstances, mine ventilation alone cannot solve the problem of high temperature heat damage. In order to ensure the normal work of employees, in most cases a corresponding cooling system must be built. With technological innovation, air cooler cooling technology has been widely used in the coal mining industry and has become one of the main methods to reduce the high temperature in the mine. Mine air coolers are generally arranged in the underground mining face or the air intake roadway of the working face, and the underground air is seriously polluted, with more coal dust, high temperature and humidity, and narrow space. The harsh working environment of the mine makes the surface of the fins easy to accumulate dust, which seriously affects the heat exchange effect of the air cooler.

The superhydrophobic surface has aroused great interest in academia and industry because of its potential applications in the fields of self-cleaning, anti-icing and anti-corrosion. Most modern coatings are synthesized to provide a hydrophobic/superhydrophobic surface. There are two essential requirements for making hydrophobic coatings: one is a low surface energy material, and the other is a micro-nano layered structure. The superhydrophobic coating has poor adhesion between the low surface energy component and the substrate, and the micro/nano structure is very fragile. When the surface is impacted, friction and other mechanical effects, it is easily damaged and loses superhydrophobic properties without high mechanical properties. The superhydrophobic coating is difficult to play a role in practical applications.

At present, the preparation of super-hydrophobic coatings/layers in the prior art mainly includes:

CN108505319A discloses an environmentally friendly superhydrophobic material and its preparation method and application. It mainly uses nanomaterials to modify the overall three-dimensional structure of the substrate material, thereby improving the roughness of the overall three-dimensional structure of the substrate material and preparing superhydrophobicity with excellent hydrophobic properties Materials, the main research method is: dissolve ferric chloride, urea, sodium dodecyl sulfonate in deionized water to obtain a mixed solution, and then add the mixed solution and the base material into a Teflon-lined autoclave Hydrothermal reaction, naturally cooled to room temperature, rinsed with deionized water, and dried to obtain environmentally friendly superhydrophobic materials;

CN109207023A discloses a controllable preparation method for an environmentally friendly hydrophobic coating on the surface of aerospace materials. The preparation method includes the following steps: dissolving epoxy resin with acetone and spraying it on a processed aerospace material substrate to obtain an adhesive layer; Then mix the zinc stearate powder and epoxy resin with mechanical stirring, add the curing agent, add an appropriate amount of acetone, mix uniformly, and spray on the adhesive layer, dry the resulting coating sample at room temperature, and then It is etched in acetic acid solution, washed and dried, modified in stearic acid absolute ethanol solution, and dried to obtain a hydrophobic coating;

CN107880770A discloses a preparation method of an environmentally friendly multifunctional super-hydrophobic coating. The preparation method mainly includes the preparation of nanometer titanium dioxide powder, the preparation of nanometer titanium dioxide powder modified by octadecyl isocyanate, silicon resin and modified The preparation of nano-titanium dioxide powder mixed coating, and coating the obtained hydrophobic coating on the substrate to obtain the super-hydrophobic coating.

The above-mentioned superhydrophobic coatings in the prior art all have superhydrophobicity, however, their mechanical durability cannot meet the requirements. With the depletion of fossil resources and the increase in people’s awareness of environmental protection, more sustainable and environmentally friendly raw materials are used to Manufacturing bio-based polymers is receiving more and more attention. In summary, it is necessary to develop an environmentally friendly superhydrophobic coating with high mechanical durability.

Summary of the invention

technical problem

The solution to the problem

Technical solutions

In order to solve the main technical problem of poor mechanical properties of the super-hydrophobic coating in the prior art, the present invention proposes a method for preparing an environmentally-friendly super-hydrophobic coating with high mechanical durability. The coating prepared by the method is Excellent mechanical durability.

In order to solve the above technical problems, the present invention adopts the following technical solutions:

A preparation method of environmentally friendly super-hydrophobic coating includes the following steps in sequence:

a Prepare waste edible oil fatty amide,

Use filtered and purified waste edible oil as a raw material to synthesize waste edible oil fatty amide through amino decomposition reaction;

b Preparation of polyurethane prepolymer,

Dissolve the waste edible oil fatty amide in acetone at room temperature to obtain a 50wt% waste edible oil fatty amide solution, add the waste edible oil fatty amide solution to toluene diisocyanate, and use dibutyltin dilaurate as a catalyst, Stir at a certain temperature to reach the pourable viscosity to obtain the polyurethane prepolymer;

c Preparation of modified polyurethane,

The polyurethane prepolymer is capped by double-ended amino-hydrocarbon-based silicone oil to obtain modified polyurethane;

d Preparation of environmentally friendly super hydrophobic coating,

Hydrophobic silicon carbide particles are treated to obtain hydrophobic silicon carbide powder, and then the modified polyurethane is mixed with the hydrophobic silicon carbide powder, magnetically stirred and sprayed on the substrate, and then dried and solidified;

In step d, the hydrophobic treatment step is: disperse silicon carbide particles in ethanol solution by ultrasonic treatment, then add double-end amino hydrocarbyl silicone oil, magnetically stir at a certain temperature to obtain a modified nano silicon carbide solution, which is washed and dried by centrifugation Then, hydrophobic silicon carbide powder is obtained;

The mass ratio of the hydrophobic silicon carbide powder to the modified polyurethane is 2-10:1.

As a preferred solution of the present invention, in step a, the preparation steps of the waste edible oil fatty amide are: first place sodium methoxide and diethanolamine in a reaction flask, turn on the heating switch and magnetic stirring device, and heat and stir at 80°C for 20 Then, add the purified waste edible oil dropwise within 60 minutes. After the purified waste edible oil is completely added, the reaction temperature is raised to 120°C and the reaction is continued at this temperature for 3 hours to obtain, The molar ratio of sodium methoxide, diethanolamine and waste edible oil is 1:45:15.

As another preferred solution of the present invention, in step b, the molar ratio of the waste edible oil fatty acid amide and toluene diisocyanate is 1:1.2, and the pourable viscosity is reached by stirring at 70° C. for 2 hours.

Further, in step c, the double-ended amino hydrocarbon-based silicone oil is added dropwise to the polyurethane prepolymer, acetone is used to adjust the viscosity of the system, and the stirring reaction is continued at 55° C. for 3 hours to obtain the modified polyurethane; The molar ratio of the prepolymer and the double-end amino hydrocarbon-based silicone oil is 1:2.

Further, in the hydrophobic treatment step, the silicon carbide particles are dispersed in the ethanol solution by ultrasonic treatment for 30 minutes, and then the double-end amino hydrocarbon-based silicone oil is added and magnetically stirred at 70° C. for 4 hours.

Further, the double-ended aminohydrocarbyl silicone oil is synthesized from hydroxy polydimethylsiloxane and 3-aminopropyl triethoxysilane.

Further, in step d, the particle size of the silicon carbide particles is 30-100 nm, and the particle shape is spherical.

Further, the mass ratio of the silicon carbide particles, the ethanol solution and the double-end amino hydrocarbon-based silicone oil is 2:3:10, and the drying temperature is 130°C.

Further, the substrate is glass, copper, aluminum or iron.

The reaction mechanism of the present invention will be briefly described below. The following is the reaction equation of modified polyurethane:

The beneficial effects of the invention

Beneficial effect

Compared with the prior art, the present invention brings the following beneficial technical effects:

In the selection of raw materials, waste edible oil is used as raw material, which not only treats waste but also reduces its pollution to the environment, and is inexpensive and environmentally friendly;

From the aspect of preparation method, the polyurethane prepolymer is capped with double-ended amino hydrocarbon-based silicone oil, which improves the crosslinking ability of polyurethane, and further enhances the bonding ability between the coating and the substrate; silicon carbide particles with excellent physical properties are used as In order to improve the mechanical durability of the coating, in order to avoid agglomeration, the silicon carbide particles are hydrophobically treated. After the hydrophobic treatment, the nano-silicon carbide has good dispersibility and can be evenly distributed in the modified polyurethane, creating a The rough micro-nano surface further improves the hydrophobic performance of the coating. Using volatile acetone as the solvent, there is basically no residue after the coating is formed; the environmentally friendly superhydrophobic coating prepared by the present invention has good mechanical properties, and the sandpaper abrasion test After that, the contact angle test was performed with the DSA100 contact angle analyzer, and the contact angle of the coating to the water droplet was measured to be above 150°.

It should be particularly noted that the hydrophobic treatment of silicon carbide particles in this application significantly improves the hydrophobic performance of the coating. For specific results, see Comparative Example 1.

Brief description of the drawings

Description of the drawings

The present invention will be further explained below in conjunction with the drawings:

Figure 1 is a flow chart of the preparation process of the environmentally friendly superhydrophobic coating of the present invention;

Figure 2 is an infrared spectrum of waste edible oil fatty amide;

Figure 3 is the infrared spectrum of the polyurethane prepolymer;

Figure 4 shows the infrared spectrum of modified polyurethane;

Figure 5 is a scanning electron micrograph of the superhydrophobic coating prepared in Example 1;

Figure 6 is a diagram showing the relationship between the contact angle and the number of wear in the embodiment of the present invention.

Invention embodiment

Embodiments of the invention

The present invention proposes a method for preparing an environmentally friendly superhydrophobic coating with high mechanical durability. In order to make the advantages and technical solutions of the present invention clearer and clearer, the present invention will be described in detail below in conjunction with specific examples.

The raw materials selected in the present invention can be purchased through commercial channels.

The preparation method of the environmentally friendly super-hydrophobic coating with high mechanical durability of the present invention is shown in Figure 1. Firstly, the purified waste edible oil is used to prepare a polyurethane prepolymer, and then a double-end amino hydrocarbon-based silicone oil is used to prepare the polyurethane prepolymer. The modified polyurethane is obtained by end-capping, and finally the modified polyurethane is mixed with the hydrophobically treated silicon carbide particles, and sprayed to obtain an environmentally friendly super-hydrophobic coating with high mechanical durability.

Example 1:

Step 1. Preparation of waste edible oil fatty acid amides, first put sodium methoxide (0.007mol) and diethanolamine (0.32mol) in a three-necked round bottom flask, turn on the heating switch and magnetic stirring device, and heat and stir at 80℃ for 20 Minutes, then add the purified waste cooking oil (0.1 mol) dropwise within 60 minutes. After the purified waste edible oil is completely added, the reaction temperature is increased to 120°C, and the stirring reaction is continued at this temperature for 3 hours to obtain the waste edible oil fatty amide;

Step 2: Preparation of polyurethane prepolymer, using waste edible oil fatty acid amide and toluene diisocyanate as raw materials to prepare polyurethane prepolymer by a one-step method. At room temperature, the waste edible oil fatty amide was dissolved in acetone to obtain a 50 wt% waste edible oil fatty amide solution. Add the waste edible oil fatty acid amide solution to toluene diisocyanate, keep the NCO/OH ratio at 1.2:1, use dibutyltin dilaurate as the catalyst, stir at 70℃ for 2h to reach the pourable viscosity to obtain the polyurethane prepolymer ；

Step 3. Preparation of modified polyurethane. Add double-end amino hydrocarbon-based silicone oil dropwise to the polyurethane prepolymer, keeping the molar ratio of double-end amino hydrocarbon-based silicone oil to polyurethane prepolymer at 2:1, and use acetone to adjust the system Viscosity, stirring and reacting at 55° C. for 3 hours to obtain silicone-modified polyurethane.

FIG 2 is a used cooking oil fatty acid amide of the infrared spectrum, wherein at 3358cm ^-1 is the stretching vibration of OH, at 2852 and 2920cm ^-1 were observed an absorption band due to symmetric and CH ₂ CH ₃ groups and non- symmetric stretching, 1357cm ^-1 and 1456cm ^-1 bending vibration peaks at ₂ CH, 1614cm ^-1 is at the peak of C = O stretching vibration of an amide group, is CN stretching vibration peak, -NC at at 1207cm ^-1 = The presence of O and -OH proves the synthesis of waste edible oil fatty amides.

Figure 3 is the infrared spectrum of the polyurethane prepolymer, where 3340 cm ^-1 is the NH stretching peak, 1725 cm ^-1 is the urethane C=O stretching peak, and 1600 cm ^-1 is the stretching peak of the benzene ring skeleton. 1230cm ^-1 is the CO stretching vibration peak.

Figure 4 is the infrared spectrum of the modified polyurethane. The 1075cm ^-1 absorption peak becomes stronger because the Si-O-Si stretching vibration peak overlaps with the COC stretching vibration peak, indicating that Si-O-Si was successfully introduced into the polyurethane main chain .

Step 4. Preparation of environmentally friendly super-hydrophobic coating. Silicon carbide particles with a particle size of 30 nanometers are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended amino hydrocarbon-based silicone oil is added and magnetically stirred at 70°C for 4 hours. The modified nano silicon carbide solution is obtained, and the hydrophobic nano silicon carbide powder is obtained after centrifugal washing and drying. Mix the silicone modified polyurethane with hydrophobic silicon carbide powder, the mass ratio of modified polyurethane and hydrophobic silicon carbide powder is 4:1, after magnetic stirring, spray on the substrate, dry and solidify to obtain the corresponding high mechanical durability Environmentally friendly super hydrophobic coating.

The contact angle of the super-hydrophobic coating to water droplets is 163° measured by DSA100 contact angle analyzer.

Figure 5 is a scanning electron micrograph of the prepared superhydrophobic coating. It can be seen from the figure that spherical silicon carbide particles are uniformly distributed in the matrix, forming a rough micro-nano surface.

The abrasion resistance of the superhydrophobic coating was evaluated by the sandpaper abrasion test. A weight of 200g was placed on the sample coated with the superhydrophobic coating, the superhydrophobic coating was in contact with the sandpaper, and the sample was moved 20 cm in the same direction. A total of 10 times. The relationship between the contact angle and the number of wear times is shown in Figure 6. The contact angle of each group of droplets in Figure 6 is greater than 150°, indicating that the superhydrophobic coating prepared by the present invention has good mechanical durability.

Example 2:

Step 1. Preparation of waste edible oil fatty acid amides, first put sodium methoxide (0.007mol) and diethanolamine (0.32mol) in a three-necked round bottom flask, turn on the heating switch and magnetic stirring device, and heat and stir at 80℃ for 20 Minutes, then add the purified waste cooking oil (0.1 mol) dropwise within 60 minutes. After the purified waste edible oil is completely added, the reaction temperature is increased to 120° C. and the stirring reaction is continued at this temperature for 3 hours to obtain the waste edible oil fatty amide;

Step 4. Preparation of environmentally friendly super-hydrophobic coating. Silicon carbide particles with a particle size of 30 nanometers are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended amino hydrocarbon-based silicone oil is added and magnetically stirred at 70°C for 4 hours. The modified nano silicon carbide solution is obtained, and the hydrophobic nano silicon carbide powder is obtained after centrifugal washing and drying. Mix the silicone modified polyurethane with hydrophobic silicon carbide powder, the mass ratio of modified polyurethane and hydrophobic silicon carbide powder is 10:1, after magnetic stirring, spray on the substrate, dry and solidify to obtain the corresponding environmentally friendly super-hydrophobic coating .

The contact angle of the super-hydrophobic coating to water droplets measured by DSA100 contact angle analyzer is 150°.

Example 3:

Step 4. Preparation of environmentally friendly super-hydrophobic coating. Silicon carbide particles with a particle size of 30 nanometers are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended amino hydrocarbon-based silicone oil is added and magnetically stirred at 70°C for 4 hours. The modified nano silicon carbide solution is obtained, and the hydrophobic nano silicon carbide powder is obtained after centrifugal washing and drying. Mix the silicone modified polyurethane with hydrophobic silicon carbide powder, the mass ratio of modified polyurethane and hydrophobic silicon carbide powder is 8:1, after magnetic stirring, spray on the substrate, dry and solidify to obtain the corresponding environmentally friendly super-hydrophobic coating .

The contact angle of the superhydrophobic coating to water droplets measured by DSA100 contact angle analyzer was 155°.

Example 4:

Step 4. Preparation of environmentally friendly super-hydrophobic coating. Silicon carbide particles with a particle size of 30 nanometers are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended amino hydrocarbon-based silicone oil is added and magnetically stirred at 70°C for 4 hours. The modified nano silicon carbide solution is obtained, and the hydrophobic nano silicon carbide powder is obtained after centrifugal washing and drying. Mix the silicone modified polyurethane with hydrophobic silicon carbide powder, the mass ratio of modified polyurethane and hydrophobic silicon carbide powder is 6:1, after magnetic stirring, spray on the substrate, dry and solidify to obtain the corresponding environmentally friendly super-hydrophobic coating .

The contact angle of the super-hydrophobic coating to water droplets is 159° measured by DSA100 contact angle analyzer.

Example 5:

Step 1. Waste edible oil fatty acid amide preparation. First, put sodium methoxide (0.007mol) and diethanolamine (0.32mol) in a three-necked round bottom flask, turn on the heating switch and magnetic stirring device, and heat and stir at 80°C for 20 minutes , And then add the purified waste cooking oil (0.1 mol) dropwise within 60 minutes. After the purified waste edible oil is completely added, the reaction temperature is increased to 120° C. and the stirring reaction is continued at this temperature for 3 hours to obtain the waste edible oil fatty amide;

Step 2: Preparation of polyurethane prepolymer. The waste edible oil fatty amide and toluene diisocyanate are used as raw materials to prepare the polyurethane prepolymer by a one-step method. At room temperature, the waste edible oil fatty amide was dissolved in acetone to obtain a 50 wt% waste edible oil fatty amide solution. Add the waste edible oil fatty acid amide solution to toluene diisocyanate, keep the NCO/OH ratio at 1.2:1, use dibutyltin dilaurate as the catalyst, stir at 70℃ for 2h to reach the pourable viscosity to obtain the polyurethane prepolymer ；

Step 4. Preparation of environmentally friendly super-hydrophobic coating. Silicon carbide particles with a particle size of 30 nanometers are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended amino hydrocarbon-based silicone oil is added and magnetically stirred at 70°C for 4 hours. The modified nano silicon carbide solution is obtained, and the hydrophobic nano silicon carbide powder is obtained after centrifugal washing and drying. Mix the silicone modified polyurethane with hydrophobic silicon carbide powder, the mass ratio of modified polyurethane and hydrophobic silicon carbide powder is 2:1, after magnetic stirring, spray on the substrate, dry and solidify to obtain the corresponding environmentally friendly super-hydrophobic coating .

The contact angle of the superhydrophobic coating to water droplets measured by DSA100 contact angle analyzer was 161°.

Comparative example 1:

This comparative example is compared with Example 1. In step 4, the hydrophobic treatment of the nano silicon carbide particles is omitted, except that the other method steps are the same. The specific operation steps are as follows:

Step 4. Preparation of the coating. Mix the silicone-modified polyurethane with silicon carbide particles with a particle size of 30 nanometers. The mass ratio of the modified polyurethane and nano-silicon carbide particles is 4:1. After magnetic stirring, they are sprayed onto the substrate. After drying and curing, the corresponding coating can be obtained.

The contact angle of the coating to water droplets measured by DSA100 contact angle analyzer is 117°

Claims

A preparation method of environmentally friendly super-hydrophobic coating is characterized in that it comprises the following steps in sequence:

a Prepare waste edible oil fatty amide,

Use filtered and purified waste edible oil as a raw material to synthesize waste edible oil fatty amide through amino decomposition reaction;

b Preparation of polyurethane prepolymer,

Dissolve the waste edible oil fatty amide in acetone at room temperature to obtain a 50wt% waste edible oil fatty amide solution, add the waste edible oil fatty amide solution to toluene diisocyanate, and use dibutyltin dilaurate as a catalyst, Stir at a certain temperature to reach the pourable viscosity to obtain the polyurethane prepolymer;

c Preparation of modified polyurethane,

The polyurethane prepolymer is capped by double-ended amino-hydrocarbon-based silicone oil to obtain modified polyurethane;

d Preparation of environmentally friendly super hydrophobic coating,

Hydrophobic treatment of silicon carbide particles to obtain hydrophobic silicon carbide powder, and then mix the modified polyurethane with the hydrophobic silicon carbide powder, spray it on the substrate after magnetic stirring, and dry and solidify to obtain;

In said step d, the hydrophobic treatment step is: dispersing silicon carbide particles in ethanol solution by ultrasonic treatment, then adding double-end amino hydrocarbon-based silicone oil, and magnetically stirring at a certain temperature to obtain a modified nano silicon carbide solution. After centrifugal washing and drying, hydrophobic silicon carbide powder is obtained;

The mass ratio of the hydrophobic silicon carbide powder to the modified polyurethane is 2-10:1.
The method for preparing an environmentally friendly superhydrophobic coating according to claim 1, wherein in step a, the preparation step of the waste edible oil fatty acid amide is: firstly placing sodium methoxide and diethanolamine in a reaction flask, and opening Heating switch and magnetic stirring device, heating and stirring at 80℃ for 20 minutes, and then adding the purified waste edible oil dropwise within 60 minutes. After the purified waste edible oil is completely added, the reaction temperature is increased to 120°C and Continue to stir and react for 3 hours at this temperature to obtain that the molar ratio of the sodium methoxide, diethanolamine and waste edible oil is 1:45:15.
The preparation method of an environmentally friendly superhydrophobic coating according to claim 1, characterized in that: in step b, the molar ratio of the waste edible oil fatty acid amide to toluene diisocyanate is 1:1.2, and the mixture is stirred at 70°C for 2 hours. Pourable viscosity.
The preparation method of an environmentally friendly superhydrophobic coating according to claim 2 or 3, characterized in that: in step c, the double-ended amino hydrocarbon-based silicone oil is added dropwise to the polyurethane prepolymer, and acetone is used to adjust the system viscosity , Continue to stir and react at 55° C. for 3 hours to obtain modified polyurethane; the molar ratio of the polyurethane prepolymer and the double-end amino hydrocarbon-based silicone oil is 1:2.
The preparation method of an environmentally friendly super-hydrophobic coating according to claim 4, characterized in that: in the hydrophobic treatment step, the silicon carbide particles are dispersed in an ethanol solution by ultrasonic treatment for 30 minutes, and then double-ended Type ammonia hydrocarbon-based silicone oil, magnetically stirred at 70°C for 4h.
The method for preparing an environmentally friendly superhydrophobic coating according to claim 5, wherein the double-end aminoalkyl silicone oil is composed of hydroxypolydimethylsiloxane and 3-aminopropyl triethoxy Based on silane synthesis.
The method for preparing an environmentally friendly super-hydrophobic coating according to claim 6, characterized in that: in step d, the particle size of the silicon carbide particles is 30-100 nm, and the particle shape is spherical.
The method for preparing an environmentally friendly superhydrophobic coating according to claim 7, wherein in step d, the mass ratio of the silicon carbide particles, the ethanol solution and the double-end amino hydrocarbon-based silicone oil is 2:3: 10. The drying temperature is 130°C.
The preparation method of an environmentally friendly superhydrophobic coating according to claim 8, wherein the substrate is glass, copper, aluminum or iron.