Tasklist
- Bead preparation
- follow the procedure you devised on Friday (this procedure scaled to produce 4.5 g of beads)
- repeat, increasing the mass percent clay to 20% (we will continue increasing each week until beads do not form)
- Crosslink films from Friday
- MG calibration curve
- Carefully examine the bottom of your bottle. Any solid particles present?
- We will use UV/Vis spectroscopy to measure MG concentrations
- The maximum absorption for any UV/Vis analysis should be 1
- You need at least 5 concentrations (as evenly distributed as possible) to make a standard curve
- PVOH film characterization
- Swelling characteristics are examined by mass before and after drying in an oven
- Crystallinity is examined using XRD
- Thermal transitions are examined using DSC
- PVOH film preparation
- Repeat the preparation of film containing clay, but use your 3 wt% solution to replace some of the water. How much do you need?
Large scale synthesis
Bead Protocol
- 30 mL of ethyl acetate + 500 uL of glutaraldehyde
- Add your PVA-clay (approximately .5 g of PVA and .051-.055g NaMT) in a dropwise manner. Immediately start timing the reaction for 2 minutes when you do the first drop.
- After 2 minutes, slowly add 7 mL of 0.2 M NaHCO3.
- Once completed, transfer to a falcon tube and centrifuge for 1 minute at 3000 rpm, rotor 41.
- When beads are separated from the organic phase, pipet out the organic phase and re-suspend the beads in distilled water.
calculations:
yield of PVOH and bentonite = 4.5 g
want 10 percent clay bentonite.
48 ml , 48 - 17 , 48/30 = 8/5 molarity .
flip -- 30/48 * 1
prepared 33 ml of 1.45 M HCl from 12.1 M concentrated HCl
for 20 percent weight:
0.45 * 2 = 0.9 g
0.9 * 100 / 3 = 30 ml bentonite mix
2.67 M HCl
weight of films (g) : .87122 glyoxal
.81073 no clay
1.15197 bentonite
on Friday, prepare clay solution with powder clay.
PVOH Dialdehyde Crosslinking
- Record mass of air dried films:
- Glutaraldehyde: 0.50790 g Glyoxal: 0.53745 g
- Heat acidic sulfate solution to 70°C
- Place films in heated solution for 60 min
- Stir bar interfered with films
- Used lowest spin setting to minimize entanglement
- Plastic buchner funnel can be used to separate bar from film, but 75 mL solution needed
- Rinsed films with deionized water (~ 5 sec)
- Glutaraldehyde film was soft, but had good integrity (clear, colorless)
- Glyoxal film had collapsed into sticky gel-like clump (translucent - white color)
- Placed films in 50 mL 1 M HCl at 70°C for 60 min (requires preheat; plan accordingly)
- Both films now transparent and rubbery
- Edges can break; care needed when handling with tweezers
- Rinsed films in water (~ 5 sec) and soak for 10 min
- Place films in 0.2 M NaHCO3 for 30 min
- Rinse films in water (~ 5 sec) and soak for 10 - 20 min
- Final rinse (~ 5 sec) and air dry for 2 days
- Noted film appearances prior to drying
- Glutaraldehyde film still had good integrity
- Glyoxal film was a clump and may have lost mass
- Both films had similar textures & colors: transparent & rubbery
Reaction happening: Addition reaction ; H20 you get Acetal when 2 alcohol and 1 Aldehyde with acid catalyst. 80 percent of crosslinking in sulfateacid, switch acids to make sure acid stays strong. need concentrated salt solution formed before adding film to HCl, dont want to dissolve it in HCl.
becomes one big molecule.
Glyoxal film needs to be done separately, see clumping above.
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