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New NANO-technology based high performance insulation FOAM system for energy efficiency in buildings

Final Report Summary - NANOFOAM (New NANO-technology based high performance insulation FOAM system for energy efficiency in buildings)



Executive Summary:

The Nanofoam project is funded by the European Union’s Seventh Framework Programme (FP7) and the Public-Private-Partnerships (PPPs) “Energy-Efficient Buildings” initiative. It has started in Jan 2012 with the aim to develop the next generation of insulating material with lower carbon footprint for use in new and existing buildings.

Through the Research and Technological Development (RTD) and Demonstration (DEMO) work packages, the project targeted to deliver the innovative high-performing nanostructured polymeric foam, employing a low GWP blowing agent such as CO2 and having a lower thermal conductivity and superior properties (mechanical, fire resistance, moisture/fungi resistance) than commercial insulation products at a competitive price.

The key objectives of the project over three year period were:

• Develop an innovative high performing nanostructured polymeric foam, employing a low Global Warming Potential (GWP) blowing agent such as CO2
• Achieve a lower thermal conductivity and superior properties (mechanical, fire resistance, moisture/fungi resistance) than commercial insulation products at a competitive price
• Evaluate and test the compliance of this technology with respect to current European standards and environmental, health and safety regulations in real scale settings (laboratory rooms or real dwellings)
• Assess the full technical, economic and environmental performance of the novel engineered insulation Nanofoam for its commercial implementation on the market as direct insulation product or as VIP core in new buildings and for the retrofitting of old ones

In July 2013, the project is currently mid-way and has completed the goals until month 18. In the mid-term review meeting, technical progresses and financial data have been thoroughly reviewed.

For making nano-cellular thermoplastic materials with supercritical carbon dioxide, the process and processing conditions were developed based on modelling and lab measurements. The experimental mini- plant equipment was designed, built and has been started-up. Although demonstration of samples with target properties is scheduled for month 24, it has been shown that until month 19, it has not been possible yet to make thermoplastic foam with cell size below 1 µm having the target porosity (>85%) in the continuous process which was the initial project goal. It is unlikely that a robust technology will exist by year-end which could be scaled up to semi-industrial size as initially set up in Work Packages 4, 5 and 6.

On the recommendation of EC and agreed by all the partners, the project is discontinued on Sept 30, 2013.

Project Context and Objectives:

Introduction

The heating and cooling of buildings account for approximately 40% percent of the overall energy consumption in Europe. Current commercialised insulating materials for building and construction have long-term thermal conductivity values between 0.023 and 0.045 W/m.K. Achieving future requirements for lower energy consumption as described in the European Energy Performance of Buildings Directive (EPBD) requires a significant increase of thickness of conventional insulators.

This will cause impractical design problems and cost increases in the building industry. High performance insulating materials available today are either not cost-effective and are too fragile to meet the durability needs that are critical for mainstream building products

Objectives

The objectives of the project are:

- Develop an innovative high performing nanostructured polymeric foam, employing a low Global Warming Potential (GWP) blowing agent such as CO2
- Achieve a lower thermal conductivity and superior properties (mechanical, fire resistance, moisture/fungi resistance) than commercial insulation products at a competitive price
- Evaluate and test the compliance of this technology with respect to current standards and environmental, health and safety regulations in real scale settings
- Assess the full technical, economic and environmental performance of the novel engineered insulation Nanofoam for its commercial implementation on the market in new buildings and for retrofitting of old ones

Project Results:

Work Packages Description

The Work Packages of the Nanofoam project consisted of two phases,

• Proof-of-Concept/Validation at Mini-Plant (WP2, WP3: Jan 1, 2012 to Dec 30, 2013)
• Semi-industrial scale up engineering and production of large samples for testing at large building facilities (WP4, Wp5 and WP6: Jun 1 2013 to Dec 30, 2014)

The reporting period M1-M21 (Jan 1, 2012 to Sep 30, 2013) covers mainly the developments in WP2, WP3 and initial work of WP4.

The objectives of these WP were:

- As Proof-of-concept, studying and modelling different single or blends of polymeric materials and assessing the interaction with foaming agents and additives/nano-additives under a range of conditions for making Nanofoam.
- Development and build-up of a novel foaming processes aiming to produce nanostructured foams using high concentration of supercritical carbon dioxide.
- Validating the theoretical proof-of-concept through screening and testing a wide number of polymer systems, nano-additives and supercritical carbon dioxide foaming agent together with engineering development of the novel processes that enable production of Nanofoam.
- Development of qualitative and quantitative methodologies for characterising and modelling the morphological, mechanical, chemical and physical properties of polymeric Nanofoam
- Development of a methodology to evaluate the compliance of the Nanofoam technology to the EU standards and environmental, health and safety regulations.
- Fine-tuning of the formulation chemistry and foaming process in order to obtain the desired and optimised Nano-structure, properties and functionalities.

The desired outcome of first phase was the definition of a chemistry and laboratory process for producing innovative Nanofoam with high insulating performance. Our targets were to achieve a pore size around 100 nm, a porosity > 85% and a λ-value less than 18 mW/m.K. Once achieving this, the concept will have to be transferred at a semi-industrial up-scaling process. The preferred strategy will be to build a new processing line or upgrade existing facilities whenever possible to achieve 1) a high performance material with acceptable economics, 2) at optimized costs.

Key achievements during the period

1) Foaming Process development

- A new semi-continuous foaming device was designed and built up. This new process enables a mixing of molten polymer with very high concentration of supercritical CO2 (30 wt%) under high temperature (up to 250°C) and very high pressure (up 300 bar).
- Different foaming die technologies were designed, built and tested safely.
- High porosity strand foams with microstructure can be produced with the device and temperature controlled die bloc. In spite of very high nucleation density, derived from high % of supercritical CO2, polymer blends and high % of nano-nucleators, or high depressurization rate, nanostructure foam with high porosity could not be produced, in contrast to the initial modelling from nucleation and bubble growth. The foam porosity is about 80 to 85% and pore size is in the range of microns instead of 100-200 nm.

2) Modeling

- The heat transport through nanoscaled as well as through microscaled foams with and without infrared opacifiers has been modelled. For this purpose the heat transfer caused by solid conduction, gaseous conduction and radiative transfer has been calculated separately. These models give the correlation between the heat transfer mechanism and the material and structural properties. Furthermore, two different methods to predict the radiative conductivity of opacified foams have been developed and validated at ZAE Bayern.
- The theoretical models were validated by the experimental measurements concerning the microscaled foams with and without opacifiers. The results of the modelling and the measurements are in a good agreement, particularly for polyurethane foam and for extruded polystyrene foam. For the nanoscaled foams a validation is still pending due to the unavailability of Nanofoam.

3) Product characterization

- A new equipment to measure the thermal conductivity of small samples was developed, which would enable to determine the thermal insulation properties of sample of diameter 20 mm and 2mm thick. This change required a significant investment (simulation, fabrication and testing) before the new equipment can be used for future research.
- Foam having microcell morphology was tested as core material for VIP (vacuum insulating panel). Low thermal conductivity of 0.0045 W/m.K (at 0.1 milibar) is measured, similar to conventional VIP made with fumed silica. At moderate vacuum (2 milibar), a λ-value of 0.010 W/m.K is obtained. Future development could help to reduce the long-term insulation performance to 0.008 W/m.K.

4) IPR and Dissemination/Publication

- No patent was filed during the working period.
- Article Thermal insulation modelling is being written and will be published in a peer-reviewed journal
- Microcell structured foam for VIP was presented at Workshop High Performance Thermal Insulation (HPI) in Wurzburg, 2013.

Resource used for the Work Packages during the reporting period

Person Month (PM) Resource per Work Packages

A total of 88.77 PM was used to accomplish the work packages

WP Type DOW ZAE CSTB CABA TOTAL
WP1 Project Management 2.09 0.90 0.81 1.05 4.59
WP2 Proof of Concept20.07 11.5 7.72 4.67 43.96
WP3 Concept validation15.38 6.48 5.69 7.19 35.0
WP4 Design semi-industrial 1.09 0.0 0.0 0.0 1.09
WP5 Build semi-industrial 0.12 0.0 0.0 0.0 0.12
WP6 Performance evaluation 0.0 0.0 0.0 0.0 0.0
WP7 Dissemination 2.13 0.79 0.30 0.79 4.01

Detailed description of achievements in Work Package WP2: Proof of Concept: NANOFOAM Engineering and Characterization

Table 3: WP 2 – Tasks and Achievements

1. Examine the fundamentals and approaches for producing Nanofoam: polymers, additives, foaming agents and processes:

A thorough selection of thermoplastic polymers (from low to high glass transition temperature) and additives (silica, graphite) was performed. The analysis was based on the capability of dissolving high percentage of sCO2 to create large number of nucleation sites needed for making nano/micro cellular morphology.

2. Up-to-date literature on polymeric nanostructured materials and identify most interested technology to be reproduced in the Lab:

Thorough analysis of solid-state foaming and of extrusion foaming lead to the selected technology which requires mixing and cooling of a polymer with at least 20 to 30 wt% of CO2 under pressure of >200bars. Through depressurized foaming, nanostructure can be produced, hence a continuous process can be envisaged. Results were reported in D2.1: R&D scoping and preliminary technology plan.

3. Identify risks (technical, EH&S, building practices) and routes to mitigate.

A complete assessment of risk was performed and a mitigation strategy was developed and reported in D2.2.

4. Identify methods to measure and model morphology, thermal conductivity, mechanical properties, FR and LCA approaches.

A comprehensive summary of analytical testing methodology was summarised and reported. The environmental assessment can be done by using different environmental assessment methods. The information can be used to support decision-making, such as industrial process optimization, or the choice of environmentally friendly products. Results have been summarised and reported in D2.3 and to D2.6 (updated of D2.3).

5. Engineer various polymers and blends with foaming agents for making Nanofoam.

A wide range of thermo plastic resins were assessed as feedstock for Nanofoam technology. The CO2-philic resins (styrenic copolymer like SMA, SAN, SANMA or Acrylate polymers like PMMA, PEMA) are the preferred options.

6. Characterize and model polymer/gas solubility, transport properties and nucleation density for selected polymers and CO2.

The model was developed using PC-SAFT model. The CO2 solubility in the polymer can then be estimated, function of their molecular properties, dispersing and hydrogen bonding. Results have been summarised and reported in D2.4.

7. Design and set up a lab-scale foaming process. Define operating conditions to achieve nanostructured material.

A major development of the project work package. A novel elongational/shear mixing and cooling device was designed to allow an efficient dissolution and dispersion of more than 20% of CO2 under high pressure in the molten thermoplastic resins. The time for dissolution of CO2 is only 30 minutes, compared to 8 to 24 hours for the solid-state foaming process. Through a rapid depressurization rate, foam with microcell structure can be created. Initial experiments were conducted with styrenic polymer to validate the process foaming feasibility. The pore size is about 10 to 50 microns with a porosity of 90-95%. Results have been summarised and reported in D2.4

8. Characterize foam morphology; measure thermal conductivity and establish transfer functions.

Investigate and model other properties such as durability, fire and moisture resistance.

Foam material were characterised in terms of porosity and cell structure. In parallel, conventional insulating material as well as microcellular foams were assessed to understand the performance and to validate the thermal conductivity and mechanical property modelling. A software (EXCEL sheet) has been developed to compute simultaneously the thermal conductivity and the Young modulus in function of the microstructure (cell size, open or closed cell, strut size & wall thickness). Results have been summarised and reported in D2.5

Conclusion of WP 2: Theoretical Proof of Concept and Modelling

Based on the initial modelling, in order to make Nanofoam structure with pore size of 100 nm, a high nucleation density of 3×1016 #/cm³ would be needed. Such a high nucleation density can be achieved with about 20 to 30% of CO2, assuming the volume of CO2 nuclei is around 2000 to 3000 nm³ (or diameter around 18 nm). Beside acrylic polymer, which has a high solubility of CO2, other thermoplastic resins have limited CO2 solubility. It is however possible to mix a very high concentration of CO2 (up to 20% or more) with the resin using the elongational/shear RMX mixer device. Through a controlled expansion from a fast depressurization process, a nanostructure could be obtained.

Single resin or polymer blends are to be assessed in order to enhance the nucleation density. The use of nano-fillers such as graphite or silica should also be considered.

Novel foaming device combining shear and elongational mixing was designed and built. This device allows mixing of very high concentration of supercritical carbon dioxide under high temperature and high pressure.

Initial foaming experiments were performed safely with styrenic copolymer resins and foams with regular cell structure were obtained. Further experiments were done and described in WP3.

The modelling presented advanced understanding of the thermal conductivity of cellular material, effect of solid conduction and of radiative heat transfer. At ZAE Bayern the heat transport through nanoscaled as well as through microscaled foams with and without infrared opacifiers has been modelled. For this purpose the heat transfer caused by solid conduction, gaseous conduction and radiative transfer has been calculated separately. As input data the material of the foam as well as the structure of the foam is needed. The bulk properties and cell morphology (i.e. cell size, strut size and cell wall thickness) influence all three heat transfer mechanisms. Open-celled foams were investigated as well as closed-cell foams.

These models give the correlation between the heat transfer mechanism on the one hand and the material and structural properties on the other hand. The results will be published in a scientific paper.

The mechanical properties are also studied and their effects on thermal insulation are assessed. The effect of microstructure (open or closed cell, cell size, strut size and wall thickness) could influence their application in building (wall, floor, ceiling …). For example, for a given Young modulus, the thermal conductivity can drastically change from open-cell foam with small cell-size and a large number of struts to open-cell foam with larger cell-size and a smaller number of struts.

List of Deliverables and delivery dates of WP2

D2.1 Preliminary Technological Plan, uploaded in SESAM on 30-April-2012
D2.2 Risk analysis and mitigation strategy, uploaded in SESAM on 30-Jun-12
D2.3 Framework for the analytical testing methodology, uploaded in SESAM on 30-Jun-12
D2.4 Modelling, tests and fine-tuning of the laboratory screening phase; Report on nanofoam engineering, uploaded in SESAM on 31-Dec-12
D2.5 Collection of representative tests on samples, uploaded in SESAM on 31-Dec-12

WP3: Concept Validation: NANOFOAM Optimization and Pilot Mini-Plant Testing

List of Tasks and Achievements of WP3

1. Fine-tuning of the formulation chemistry in order to obtain the desired nano-structure, properties and functionalities.

This task will run in parallel with all the other activities in the concept validation phase. Various polymer chemistry and blends, together with high CO2 have been fine tuned for making nanocellular structure.

Conventional insulating foam as well as microcellular foams were also tested and validated for the modelling. Report on nanofoam engineering: modelling, tests and fine-tuning of the concept validation phase are to be reported as D3.1

2. Engineer a semi-continuous foaming process for the production of Nanofoam. This is a major development of the project, in which the novel elongational and shear mixing and cooling continues to be upgraded enabling a better control of processing operation and foaming.

Several equipments (mixing bloc, die bloc, die gates) were designed and built, function of the progress from foaming understanding. Blueprints of final layout of the pilot mini-plant is summarized in D3.2.

3. Build the mini plant preferably in Switzerland. Ensure equipment complying with safety standards.

The equipment is built according to the process safety at Dow Chemical and in full compliance with EU process standards. The new equipments and new die blocs were tested and operational successfully. Maintenance is an issue due to stringent required processing conditions (high pressure >200 bars, high temperature). Continued investigations are performed to provide a full controllable mixing and foaming. The results are reported in D3.3

4. Drive mini-plant testing experiments and material characterisation. Fine-tuning of the formulation chemistry and foaming process in order to obtain the desired and optimised Nano-structure, properties and functionalities Define best technology for achieving Nanofoam

Various polymer chemistry and blends, together with high CO2 have been fine tuned through using Designs of Experiments (DOE) to produce the Nanofoam material. Effects of pressure and temperature as well as nanofillers on foaming are being characterized. Although the nucleation sites were high enough, challenges were observed for making nanocell structure. The lowest pore size that can be achieved is about 5 to 10µm, with porosity of about 85 to 90%. Reducing the pore size to less than 1µm will probably lead to much lower porosity, hence economically unfavourable. The results are reported in the final report.

5. Thermal conductivity measurement

As only samples of small sizes would be produced, CSTB developed and manufactured a kit which can implemented in a Heat Flow Meter to measure thermal conductivity of small samples.

The developments can however be leveraged for making microcellular material which can be used as core material for Vacuum Insulation Panel (VIP). Initial thermal conductivity measurement showed excellent performance and could further lead to a better substitution of summed silica core material for VIP. The results are reported in the final report.

Key Results from WP3

Foaming experiments and results

- A new semi-continuous foaming device and different foaming dies were designed and built up. This new process enables a mixing of molten polymer with very high concentration of supercritical CO2 (30 wt%) under high temperature (up to 250°C) and very high pressure (up 300 bar). Equipments operated safely and complied with high pressure/high temperature manufacturing safety standard
- Various die blocs and die gates were designed, built and tested with conventional PS resin and CO2 mixtures. The optimum design which enables high depressurization rate, reliable and reproducible foaming experiments was then selected and implemented.
- Various styrenic and acrylic copolymers and polymer blends were tested as feedstock for foaming. Initial modelling with CO2 concentrations indicates a linear increase of number of nucleation density, hence a higher the %, the smaller the pore size. In the real foaming experiments, the nucleation density is not the one that governs the bubble size, but the bubble growth rate leads to the final size.
- It is hypothesised that the coalescence of bubbles due to a fast diffusion and low viscosity resins lead to large pore size, particularly when the CO2% exceeds the solubility limit in the polymer. The pore size reaches a plateau, when CO2 exceeds 15-20%. Furthermore, irregular structure resulted when CO2 exceeded the solubility limit
- Attempt to freeze off the bubble growth in the semi-extrusion foaming process was not successful. When cooling the temperature to below 80°C, the system is frozen off and no more flow can go through the die bloc.
- Effect of nano-nucleators to enhance nucleation density. Although the # of nucleation is increased, thanks to the platelet structure of graphite, the reduction in pore size is not significant as expected.

Thermal Insulation Modeling and results

- Thermal conductivity and mechanical property modelling of cellular material were performed and leveraged to micro and nano-cell structure. Also two different methods to predict the radiative conductivity of opacified foams have been developed and validated at ZAE Bayern. The theoretical models were validated by the experimental measurements concerning the microscaled foams with and without opacifiers. The results of the modeling and the measurements are in a good agreement, particularly for polystyrene and polyurethane foams. Furthermore the results derived at ZAE Bayern were compared with measurements performed at CSTB and at DOW. These results are in a good agreement, too, as discussed in the report.
- Nevertheless, for the nanoscaled foams a validation is still pending due to the unavailability of nanofoams. Additionally the model for nanoscaled foams need to be improved for correctly describing the correlation between the nanoscaled foam structures and the heat transfer mechanism. Especially the description of scattering of infrared radiation at the nanoscaled foam structure (which is different from the structures of other porous materials such as aerogels) including dependent scattering need to be improved. The situation becomes even more complex if nanoscaled opacifiers are added.

Microcell foam for modelling and VIP

- Opacified foams (nano-filled foams) with reduced cell-sizes in the lower microscale range and with a porosity of 95% were investigated. After investigating these foams, the foams were used as core material for vacuum insulation panels. The VIP were prepared and characterized at ZAE Bayern.
- There was no problem for making VIP. Thermal conductivity measurement indicated similar performance like conventional VIP made with fumed silica (0.004-0.005 W/m.K at 0.1 milibar). At a very moderate vacuum (2 milibar), equivalent to long-term performance, λ-value is about 0.010 W/m.K.

New equipment to measure the thermal conductivity of small samples.

- As only samples of small sizes would be produced, CSTB was forced to modify its measurement system in order to meet this demand. With this new equipment, sample of diameter 20 mm and 2mm thick can be now characterized. This change required a significant investment (simulation, fabrication and testing) before the new equipment can be used for research. The equipment is being validated and could be considered in other R&D/FP7 developments.

Conclusion of WP3: Optimization and Validation at Mini-Plant Testing

The objective of the proof-of-concept phase and the validation phase is the definition of a chemistry and a process for producing innovative Nanofoam with high insulating performance, hence the technology can be scaled up to the semi-industrial scale in the next phase.

- We have demonstrated a novel engineering process for making foam with micro-cellular structure, but at present, the developed technology did not yet produce a foam product meeting the project targets of 100 nm pore size with >85% porosity as targeted.
- The current results of the screened technologies (high elongational mixer or batch foaming process or extrusion foaming) do not provide a sufficient basis for semi-industrial scale-up as defined in the next Work Packages WP4, WP5 and WP6. The time-point for scale-up has been planned too early.
- Achieving the Nanofoam product requires a major R&D effort, for which this projects does neither provide the required capital nor time.
- The new microcell technology and the models developed for thermal insulation and mechanical properties enable us to leverage the current results to a new microcellular material which could offer superior performance over conventional styrenic foam materials. Initial assessment of micro open cell products as core material for VIP demonstrated a durable and excellent thermal conductivity even at moderate vacuum. This material could offer an alternative to the current fumed silica core material with a substantial cost reduction. The microcellular technology could be scaled up to a larger foaming scale quite rapidly with high success rate for delivering a commercial product.
- A new equipment to measure samples of small sizes (diameter: 20mm, thickness: 2 mm) is now available, it’s a very interesting equipment especially to measure advanced insulating materials such as aerogel or other nano-porous materials

Potential Impact:

Final conclusion

- To date, in the lab experimentation, it was possible to demonstrate nano-porous structures via batch foaming but it has not been possible to reduce cell sizes below 1μm with target porosity in the continuous process which was the initial project goal.
- Consequently, the planned technical scale-up is not possible at this point in time and the project is then discontinued.

Impact:

Based on the foreground results obtained within the Nanofoam project, the impact is rather limited.

List of Websites:

www.nanofoam.eu