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 www.ijs.si 2) Melamin d.d., Kočevje, Slovenia www.melamin.si bojan.zajec@ijs.si 20. - 22. 09. 2012 The Energy & Materials Research Conference

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

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

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 120-160°C, few minutes up to ½ hour (temp. distribution!) current production at lab. scale, pilot line is under construction

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

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 4h @150°C  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 drying @150°C 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  = 55-85 kg/m3 MF rigid foams are UHV compatible and candidate for core material.

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

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))

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 

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

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

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

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)

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 bojan.zajec@ijs.si