Using Polymers in SDM

Contents: Mixing and Pouring Process and Safety Safety attire Handling equipment: Emergency procedures: Mixing Procedure: Waste Disposal Polymer Properties Basics Mixing and Curing Moisture Sensitivity Storage During Casting Material Properties Multi-Polymer Curing and Bonding UV resistance enhancer (urethane rubbers) Embedding Materials Fabrics Partially Embedded Components

Jonathan Clark demonstrates respirator safety attire:

Mixing and Pouring Process and Safety

Note: The chemicals used for SDM are two-part castable urethanes, silicones and epoxies. These are not particularly hazardous, however they should be mixed and poured in a fume hood and care should be taken to avoid skin contact.

1. Contact MarkCutkosky about Safety Training requirements before using the RPL.

• General safety/ emergency preparedness (EHS-4200-WEB)
• Chemical safety (EHS-1900-WEB)
• Respirator Use and Fit (EHS-5300), for those wearing respirators
• For other required training, refer to http://www.stanford.edu/dept/EHS/prod/researchlab/Lab_Training_Poster.pdf

2. See Stanford Lab Safety Basics for a good introduction to handling polymers and other chemicals.

3. Before working with any of the polymers, read the data sheets that are stored with them regarding safety procedures. Most of the urethanes and silicones that we use are not particularly dangerous, however you should always work under a fume hood and wear proper attire. See

• See Special note about di-isocynates

Safety attire

Safety glasses or goggles, gloves, lab coat. See Personal Protective Attire for general instructions on safety attire. In particular, for pouring or mixing any of the polymers:

• Wear purple nitrile gloves (in the drawer below the fume hood)
• If there is a danger of splashing (not the case with most of our polymers, which are quite viscous), use goggles
• For some polymers it may be necessary to wear the green over-gloves.
• For some polymers it may be necessary to use a respirator. Any persons working with such polymers must be trained in respirator use. See EH&S respirator FAQ sheet.
  • Respirator REQUIRED for the following:
    • Any "Crystal Clear" product (Smooth-On)
    • "Smash!" Plastics (Smooth-On)
    • Clear Flex 50 & 95 (Smooth-On)
    • Task 12 (Smooth-On)

Handling equipment:

• See https://suehsaps2.stanford.edu/lcst/?q=node/13 for general information on handling equipment for chemicals
• plastic cup or beaker for mixing
• tongue depressor/popsicle stick (or other disposable mixing implement) Metal, glass or plastic stirrer to avoid moisture contamination
• Ziploc bag for waste
• Paper towels
• (any items you will embed, see below)

Emergency procedures:

• https://suehsaps2.stanford.edu/lcst/?q=node/13

Mixing Procedure:

In some cases it is advisable to use green forearm gloves over the disposable nitrile gloves:

Pouring in the fume hood, on a digital scale:

The process:

1. Mask off the area around your part (or the whole block if your parts cover it) with tape. This will keep the polymer from spilling everywhere before it cures.
   • Some people recommend putting the block into the vacuum chamber and de-gassing at this point. This will help remove any air bubbles in/around the tape.
2. Estimate how much polymer you will need; you'll want to cover your part by a layer of 1-2mm of polymer. This layer will trap any left over air bubbles so they don't stay in your part. It's best to over-estimate; we're always throwing away old/bad polymers.
3. Shake both parts of the polymer thoroughly. Especially for urethane rubber Part B and both parts of Task plastic.
4. When mixing, it is best to pour the thicker of the two parts first (Part B for urethane rubbers). The thinner is easier to control and you'll have better luck getting the exact proportions. There should be a sheet of mix ratios in the RPL, or look here
   • If mixing by volume, find a graduated beaker. They are scarce, so if possible mix by weight.
   • If mixing by weight, use a plain cup (don't waste a graduated beaker!).
   • Once you have the right proportions, mix the two parts of the polymer vigorously and thoroughly. You'll introduce bubbles, but we'll remove them later.
5. Clean off the threads of the polymer bottles before you close them. The unmixed parts will harden and seal the bottles if you don't.
6. Pour the polymer over your part, making sure to cover it completely.
7. Move the wax block into the vacuum chamber and close the lid.
8. Start the pump and de-gas for a few minutes. The polymer should bubble vigorously as the air escapes. Once the bubbles settle down you can stop the pump and slowly let the air back in.
9. The next step depends on whether the polymer you poured is hard and can be planed after curing or is soft and cannot.
   • If the part is hard, skip to the next step.
   • If the part is soft, you want to remove the polymer over your part. You can try to squeegee it off using another tongue depressor, or (if the surface finish is important) stretch a piece of teflon film over it to squeeze the excess polymer out and create a flat surface. Try to keep this excess material from spilling all over the place.
10. You can leave the part to cure in the vacuum chamber, or move it back into the fume hood. Moving it back into the fume hood is probably best, otherwise someone might have to move your block for you.
11. CLEAN UP!!! Please keep the area as clean as possible. Wipe up any spilled and uncured polymer. Place everything (mixing implements, paper towels, and gloves) in the ziploc bag you have ready and put it in the blue hazardous waste bin.

Disposal of used containers, tools:

Waste Disposal

To get the hazardous waste bucket emptied, fill out the form found here:
http://www.stanford.edu/dept/EHS/prod/enviro/waste/pickup/WastePickup_form.htm
Make sure there is a Hazardous Waste tag on the bin when they come pick it up. The table below provides most of the info needed to fill out the online form and the tag.

Building 02-530, Room 129A: just estimate the volume of waste in the garbage can.

Description	Ingredients	Toxic?	Reactive?	Flammable?
10A Resin	modified diphenylmethane diisocyanate contains MDI	X		X
10A Hardener	none	X
35A Resin	modified diphenylmethane diisocyanate contains MDI	X		X
35A Hardener	none	X		X
90A Resin	modified diphenylmethane diisocyanate contains MDI	X		X
90A Hardener	none	X		X
72DC Resin
72DC Hardener
Quik-Cast A	modified diphenylmethane diisocyanate, 12-19% With MDI, 44-50% methylene bisphenylisocyanate, 33-38% concentration polymeric plasticizer, 35-40% triethyl phosphate, <2%	X	X
Quik-Cast B	Polyether polyols amine based, 50% polymeric plasticizer, 50%	X

Polymer Properties

The following tables should be located in the RPL as well for quick reference. Please update these with as much data as is available (and add the polymer to the all tables) when we get new polymers.

The tables include:

• Basics - Hardness, Color, Manufacturer, Type
• Mixing and Curing - Working Time, Cure Time, Mix by Weight, Mix by Volume
• Material Properties - Tensile Strength, Elongation, Young's Modulus
• Curing and Bonding - Which polymers cure/bond to which other polymers

Basics

Organized by Manufacturer

Name	Hardness	Color	Manufacturer	Type	Tech Data
Dragon Skin	10A	Translucent White	SmoothOn	Silicone (Platinum Cure)	http://www.smooth-on.com/tb/files/DRAGON_SKIN_SERIES_TB.pdf
EcoFlex 0010	00-10	Clear	SmoothOn	Silicone (Platinum Cure)	http://www.smooth-on.com/tb/files/Ecoflex_Series.pdf
Vytaflex 10	10A	Translucent-Amber	SmoothOn	Urethane
Vytaflex 20	20A	Translucent-Amber	SmoothOn	Urethane
Vytaflex 40	40A	Off-White	SmoothOn	Silicone
SmoothCast 60D	60D	Amber	SmoothOn	Silicone
SmoothCast 61D	61D	Amber	SmoothOn	Silicone
SmoothCast 305	70D	White	SmoothOn	Silicone
SmoothCast 326	72D	Clear-Amber	SmoothOn	Silicone
SmoothCast 327	72D	Clear-Amber	SmoothOn	Silicone
Task 3	80D	White	SmoothOn	Urethane
Task 9	85D	Clear	SmoothOn	Urethane
IE-10AH	10A	White	Innovative Polymers	Urethane
IE-20AH	20A	White	Innovative Polymers	Urethane
IE-50AC	55A	Clear	Innovative Polymers	Urethane
IE-60A	55A	Cream	Innovative Polymers	Urethane
IE-72DC	80D	Clear	Innovative Polymers	Urethane
P-20	20A	Translucent	Silicones Inc/Innovative Polymers	Silicone	http://www.silicones-inc.com/p20.pdf
P-44	42A	Translucent	Silicones Inc/Innovative Polymers	Silicone
P-70	58A (70A, 1 week+)	Light Green	Silicones Inc/Innovative Polymers	Silicone
P-100	80A +/- 10A	Tan/Beige	Silicones Inc/Innovative Polymers	Silicone
GI 1040	30A (40A, 1 week+)	Light Blue	Silicones Inc	Silicone (Tin Cure)
Silastic S	26A	Green	DowCorning	Silicone	http://www1.dowcorning.com/DataFiles/090007c880002438.pdf
Sylgard 170	40A	Dark Gray/Black	DowCorning	Silicone
TAP Blue	26A	Light Blue	TAP Plastics	Silicone (Tin Cure)	http://www.tapplastics.com/uploads/pdf/Product%20Bulletin%207BRev.pdf
EPM-2492	75A	White	NuSil	Silicone
FXRite 12	12A	Translucent	ArtMolds	Silicone

Mixing and Curing

Working time is how long you will have to pour the part, while cure time is how long you need to wait before you remove it.

Name	Working Time	Cure Time	Mix by Weight	Mix by Volume
Dragon Skin	20 minutes	5 hours	1A:1B	1A:1B
EcoFlex 0010	30 minutes	4 hours	1A:1B	1A:1B
Vytaflex 10	30 minutes	16 hours	1A:1B	1A:1B
Vytaflex 20	30 minutes	16 hours	1A:1B	1A:1B
Vytaflex 40	30 minutes	16 hours	1A:1B	1A:1B
SmoothCast 60D	5 minutes	20 minutes	?	1A:1B
SmoothCast 61D	7 minutes	60 minutes	?	1A:1B
SmoothCast 305	7 minutes	30 minutes	10A:9B	1A:1B
SmoothCast 326	8 minutes	60 minutes	?	1A:1B
SmoothCast 327	15 minutes	4 hours	?	1A:1B
Task 3	20 minutes	90 minutes	120A:100B	1A:1B
Task 9	7 minutes	4 hours	115A:100B	1A:1B
IE-10AH	10 minutes	10 hours	?	?
IE-20AH	12 minutes	10 hours	100R:100H	?
IE-50AC	12 minutes	4 hours	50R:100H	51R:100H
IE-60A	10 minutes	8 hours	25R:100H	22R:100H
IE-72DC	15 minutes	6 hours	100R:50H	100R:55H
P-20	60 minutes	18 hours	10A:100B	?
P-44	60 minutes	24 hours	10A:100B	10.9A:100B
P-70	60 minutes	24 hours	10A:100B	13.9A:100B
P-100	60 minutes	24 hours	10A:100B	13.2A:100B
GI 1040	2.5 hours	18 hours	10:1	100:11.3
Silastic S	45 minutes	7 hours	?	10A:1B
Sylgard 170	15 minutes	24h @ 25C°, 20min @ 70C°	1A:1B	1A:1B
TAP Blue	30 minutes	8 hours	10A:1B	9A:1B
EPM-2492	2 hours	6 hours	1A:10B	?
FXRite 12	60 minutes	12 hours	10:1	10:1

Moisture Sensitivity

Storage

Ambient moisture can greatly reduce the shelf life of the individual parts. In order to combat this we are purchasing a dry gas blanket can from Smooth-on (looks and works like the Endust cans for dusting computers). Basic procedure is to almost close the container and spray the gas for a couple seconds into the container displacing the ambient air and moisture from inside then immediately finishing sealing the container.

Note: please make sure to clean off the edges of the bottle lip and lid before trying to close it because if we don't then we will have to break the lid to open it.

During Casting

Ambient moisture can inhibit the cure of urethane rubbers and plastics and cause some bubbling. Apparently by using a wooden stirrer, we are guaranteeing that we introduce moisture during mixing. It is recommended to only use metal, glass and plastic containers and stirrers.

Note: We can try using the Dry Gas Blanket stuff to ensure molds have less moistures by blanketing the cavity. The gas used is both heavier than air and removes moisture.

Material Properties

Tensile Strength and Young's Modulus were measured experimentally in some cases, see YoungsModuliForUrethanes for details. If the measured value differed from the manufacturer's data, it is indicated in bold and parentheses.

Name	Tensile Strength(measured)	Elongation	Young's Modulus
Dragon Skin	475 psi	1000%	?
EcoFlex 0010	200 psi	800%	?
Vytaflex 10	160 psi	1000%	?
Vytaflex 20	200 psi	1000%	195 kPa
Vytaflex 40	522 psi	660%	?
SmoothCast 60D	2200 psi	30%	?
SmoothCast 61D	1800 psi	20%	?
SmoothCast 305	3000 psi	?	?
SmoothCast 326	3170 psi	?	425 MPa
SmoothCast 327	3170 psi	?	425 MPa
Task 3	6650 psi	6%	?
Task 9	7800 psi	6%	?
IE-10AH	150 psi	?	?
IE-20AH	200(190) psi	175%	217 kPa
IE-50AC	1000 psi	470%	?
IE-60A	1000(200) psi	470%	560 kPa
IE-72DC	8000 psi	2%	?
P-20	525 psi	425%	?
P-44	600 psi	150%	?
P-70	775 psi	250%	?
P-100	470 psi	345%	?
GI 1040	525±25 psi	?	1550±175 kPa
Silastic S	1000 psi	900%	?
Sylgard 170	?	?	?
TAP Blue	580 psi	?	?
EPM-2492	200 psi	250%	11 MPa
FXRite 12	?	?	?

Multi-Polymer Curing and Bonding

This table quickly outlines which polymers will cure on other polymers, and how well they bond together. This does not indicate anything about how well small features will come out if the base polymer is used as a mold for the curing polymer. A color-coded, excel version of the table can be found here.

Cure options:

• full cure - the polymer cures completely on top of the base
• top cure - the portion of the polymer exposed to air cures, but the polymer in contact with the base does not.
• no cure - the polymer does not cure.

Bond options (in decreasing strength):

• full bond
• bond
• mild bond
• no bond

Cured Polymer	Base Polymer
	Vytaflex 10	Vytaflex 20	Vytaflex 40	IE 20	P-20	P-44	P-70	P-100	GI 1040	Sylgard 170	TAP Blue
Vytaflex 10	full cure full bond	full cure bond	full cure bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond		full cure no bond	full cure no bond
Vytaflex 20	full cure full bond	full cure bond	full cure bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond		full cure no bond	full cure no bond
Vytaflex 40	full cure full bond	full cure bond	full cure bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond		full cure no bond	full cure no bond
IE 20	full cure mild bond	full cure mild bond	full cure mild bond	full cure full bond	full cure no bond	full cure no bond	full cure no bond	full cure no bond		full cure no bond	full cure no bond
P-20	no cure no bond	no cure no bond	no cure no bond	full cure no bond	full cure mild cure cure	full cure no bond	full cure no bond	full cure mild cure		full cure no bond	no cure no bond
P-44	top cure no bond	top cure no bond	top cure no bond	full cure no bond	full cure full bond	full cure full bond	full cure full bond	full cure full bond		full cure mild cure	no cure no bond
P-70	no cure no bond	top cure no bond	top cure no bond	full cure mild cure	full cure full bond	full cure full bond	full cure full bond	full cure bond	no cure no bond	full cure full bond	no cure no bond
P-100	top cure no bond	top cure no bond	top cure no bond	full cure no bond	full cure full bond	full cure full bond	full cure mild cure	full cure bond		full cure mild cure	no cure no bond
GI 1040		full cure no bond
Sylgard 170	no cure no bond	no cure no bond	no cure no bond	full cure no bond	full cure bond	full cure full bond	full cure full bond	full cure full bond		full cure full bond	no cure no bond
TAP Blue	full cure no bond	full cure no bond	full cure no bond	full cure no bond	full cure bond	full cure mild cure	full cure full bond	full cure full bond		full cure mild cure	full cure full bond

UV resistance enhancer (urethane rubbers)

Smooth-On makes a UV resistance enhancer called SunDevil. This should help with the problem of UV degradation in the flextures. We need to learn how much to add without inhibiting the cure. The basic usage is to mix SunDevil (1% of total weight) with Part B and then mix Part A with that combination.

Embedding Materials

These are some quick tips and trick for embedding simple materials/components. More advanced techniques can be found on the SDMAdvancedTechniques page.

Fabrics

Fabrics embedded in soft polymers can be used to keep the part from stretching (or from stretching in a particular direction, depending on the fabric) while maintaining the ability to flex. A great example of this are Rise.StickyBot's toes.

Embedding the fabric will usually result in trapped air bubbles, so extra steps must be taken. One approach that works fairly well is outlined below, but feel free to experiment with other combinations of de-gassing and pre-coating the fabric.

Approach 1:

1. Pour the part as described above, including de-gassing it.
2. At the same time, coat the piece of fabric with some mixed polymer, making sure the polymer soaks in. De-gas this with the main part (i.e. set it somewhere on the wax block when you de-gas). You probably want to have some tweezers to manipulate the soaked fabric. Make sure you CLEAN them off when you're done.
3. Carefully place the fabric in the part, avoiding creating trapped bubbles as much as you can, and de-gas again. The first de-gas step should limit the trapped air in this step, which should keep the polymer from bubbling the fabric out of you part.
4. Carefully adjust the location of the fabric with the tweezers if it moved significantly during the second de-gassing step.
5. Cure and remove as usual.

Partially Embedded Components

Sometimes you might want to partially embed components so that portions of them are not covered in polymer. Some examples include LEDs or the nitinol flexures in the ZMan toes.

1. Design your part to include the actual part you want, plus some space for the extruding components to sit (ex. room for LED leads).
2. Before pouring the mixing or pouring the polymer, place the component how you would like it to be embedded in the part. You will need to fill the extra space you created with the green clay we have. Use this to help position the component as well.
3. Make sure the clay fills only the extra space and does not spill into the area of your part.
4. Pour the part as usual.
5. When you remove the part, simply clean away the clay and you'll be left with your part and extruding components.