1. Vacuum insulation with melamine-formaldehyde rigid
foams as core material
Bojan Zajec1, Marko Žumer1, Vincenc Nemanič1,
Nataša Figar2, Igor Mihelič2
1) Jožef Stefan Institute, Ljubljana, Slovenia
2) Melamin d.d., Kočevje, Slovenia
The Energy & Materials Research Conference

2. Outline Vacuum insulation panels (VIP)
Melamine-formaldehyde (MF) foams
Are MF rigid foams suitable for vacuum?
MF rigid foams in VIP envelope
pressure rise (lifetime)
thermal conductivity
Conclusions

3. Vacuum insulation panel (VIP)
envelope
flat
VIP,
stable
core
needed
Dewar bottle
(vacuum flask),
cylindrical
+ porous
support
(core)
porous core
very low thermal conductivity only at low internal p
typical core materials:
- nanoporous silica
- glass microfibers
- open-porous PS and PU foams
Basic physical requirements for VIP:
extreme seal tightness and very low envelope permeability for all gases
extremely low outgassing of the core material
porosity of the core preserved also at 1 bar (i.e. 10 ton/m2)
J. Fricke et al., 2006

4. Melamine-formaldehyde (MF) duroplastic foams
properties:
- variable density 2 – 150 kg/m3 [flexible  rigid foams]
- chemically inert, non-flammable (self-extinguishing), non-toxic, non-dispersible
- no degradation up to 200°C
- very good thermal and acoustic insulative properties, in air = 25 – 50 mW / m K
- MF resins have a long history of applications in aero- and automotive industry, space
technique, building construction, kitchen utensils, etc.
- approx. 4 times lower cost of production compared to PU foams
synthesis:
1. preparation of MF pre-polymer (resin)
2. preparation of the emulsion [MF resin + blowing agent (pentane) + emulsifier +
hardener (formic acid) + viscosity regulator (H20) + minor additives]
3. foaming and hardening at °C, few minutes up to ½ hour (temp. distribution!)
current production at lab. scale, pilot line is under construction

5. Melamine-formaldehyde (MF) rigid foams
density above 50 kg/m3  rigid foam
 compressive strength up to 2 MPa
~20 cm
SEM images
pore size distribution
depend on the emulsion
preparation parameters

6. Are MF rigid foams suitable for vacuum?
Polymers normally release large amounts of gases (water) when evacuated + unstable
at elevated temp. Thermal pre-treatment is mandatory for long-term outgassing reduction.
Outgassing intensity of MF rigid foams after certain heat pre-treatment ???
custom made SS UHV tight vessels
with SRG thimble & Cu tube for connection
to all-metal UHV pumping system, TIG welded
int. diam.=15 cm, V450 cm3, Vfoam353cm3
For empty vessel:
After  dp/dt ~ 10-9 mbar/s ,
Q = (0.4 – 4)×10-10 mbar L/s
[1 mbarL ~ 2.45×1019 molec.]
Very low background outgassing 
SRG
thimble
mesh
foam
mesh
Thermal pre-treatment of MF foam:
1. Air for 17h, m5-8%
2. evacuated in the vessel: 150°C for 4 hours
SRG measurements:
dp/dt  3×10-9 mbar/s 
for MF foams with  = kg/m3
MF rigid foams are UHV compatible and candidate for core material.

7. Are MF rigid foams suitable for vacuum?
Monitoring of gases being released from the MF foam (during cool down), using
Quadrupole Mass Spectrometer:
temperature
H20 N2
CO2 H2
H20 is
prevalent

8. MF rigid foams in our VIP envelope
VIP envelopes made of stainless steel (no permeation & degradation).
top frame
TIG
top 100m foil
side support
(U-profile, 0.5mm thick)
TIG welded & He leak tested. Max. dimensions 270x270mm, 20mm thick MF foam.
Some problems with foil wrinkling.
Two ports: - one for connection to the vacuum system (via Swagelok valve)
- one for SRG pressure measurements (later capacitance manometer (CM))

9. Pressure rise dp/dt measured at R.T. for 24h or more with SRG:
MF rigid foams in our VIP envelope – pressure rise meas.
VIP envelopes made of stainless steel (no permeation & degradation).
MF rigid foam thermal pre-treatment similar as before:
1. 17h drying at 150°C in air
2. evacuated in the VIP envelope, at 150°C for 8 up to 20h hours
Pressure rise dp/dt measured at R.T. for 24h or more with SRG:
p ~ 10-4 mbar
dp/dt = 2...5×10-9 mbar/s , approx. 10 years to reach 1 mbar 

10. MF rigid foams in our VIP envelope –  measurement
Thermal conductivity  of the central part of our VIP prototypes with MF rigid foam was
determined in thermal conductivity apparatus.  versus p was also determined.
10×10cm
central part
precise
leak valve
Upper plate, T=20°C
Swagelok
valve
VIP
gas
UHV
pumping
system
Lower plate, T=0°C
CM gauge
10-3 – 10 torr

11. MF rigid foams in our VIP envelope –  measurement
wet kitchen sponge in PVC bag was used to ensure good thermal contact
thermal conductivity apparatus
precise leak
valve CM
vacuum
gauge

12. MF rigid foams in our VIP envelope –  measurement
few days after end of pumping:  in center = 6-7 mW m-1 K-1
non-evacuated
35 mW m-1 K-1

13. few days after end of pumping:  in center = 6-7 mW m-1 K-1
Further decrease of  is possible
with opacifiers – less radiative
thermal transport
M Alam et al.,Appl. Energy, 88,p.3592,(2011)
R Baetens et al.,En. and Bldgs., 42,p.147,(2010)

14. Thank you for your attention.
Conclusions
MF rigid foams are the first promising organic candidate for core of VIP
very low outgassing after simple th. treatment (excel. therm. stability) lifetime!!
rigid structure – no need for pre-packing, no danger for small part. inhalation
4-5 times lower production cost compared to conv. PU foams
stainless steel envelope – no H2O permeation, no aging & degradation like polym.
Thank you for your attention.
We are looking for partners (consortium) for the coming last FP7 project call on energy efficient buildings & insulation