Search

As a new generation ofthermal insulation materials, theeffective thermal conductivityofaerogeland its composites is extremely low. The nanoporous structure of aerogels demobilises the movement of gas molecules, and the nano-skeleton system restricts solid heat transfer because of the size effect. Numerous research and modelling works have been carried out to understand and predict heat transfers. This review thoroughly discusses the existing theories and models ofsilica aerogelcomposites in gas, solid andradiative heat transfers. It investigates the correlation of the pore size distribution and solid skeleton network of the composites with thethermal conductivity. The review then assesses the advances of the development and questions remaining for further development, including 1) some unexplainable performance of existing models and 2) improvements required for gas and solid thermal conductivity models. Bridging the identified research gaps shall lead researchers to understand existing models better, develop a more accurate model based on more realistic microstructure simulation and further innovate the models for other emerging composites.

Fatty acids and fatty alcohols have the advantages of high latent heat of phase change,good thermal stability, no corrosion, no supercooling and phase separation. They can be used as phase changeenergy storagematerials for passive temperature control. However, their popularization and application are limited because of their high phase transition temperature and narrow phase transition range. This study develops a novel binary compositephase change materials(PCMs) of Capric acid (CA) and Octadecanol (OD) by amelt blendingmethod. The theoretical calculation and hot melt-step cooling were carried out to generate an optimalmolar ratio, followed by DSC thermal characterization. ATR-FTIR and XRD were performed to determine the phase transformation and chemical and structure changes. The results showed the binary CA-OD binary composite PCMs has a high latent heat of fusion, a melting temperature Tm=26.48°C and △H=181.06J/g at optimal mass ratio of 85.15:14.86 (CA:OD), which is higher than the theoretically predicted latent heat of phase transition, indicating a goodsynergistic effectbeneficial to energy storage. Solid CA exists in the form of dimer and –OH in solid OD exists in form of association, andintermolecular hydrogen bondsweakens in liquid. There are hydrogen bonds in the CA-OD binary composite PCMs, and the molecular structure changes before and after the phase transformation were similar to that of a single component CA or OD. The crystal structures of the two compounds also change and the latent heat of phase transformation is improved. Finally, through TG and high and low temperature cycle test, CA-OD binary PCMs demonstrates good thermal stability and practicability in the field ofbuilding energy conservation.

Buildings contribute to 40% of total global energy consumption, which is responsible to 38% of greenhouse gas emissions. It is critical to enhance the energy efficiency of buildings to mitigate global warming. In the last decade, advances in thermal energy storage (TES) techniques using phase change material (PCM) have gained much attention among researchers, mainly to reduce energy consumption and to promote the use of renewable energy sources such as solar energy. PCM technology is one of the most promising technologies available for the development of high performance and energy-efficient buildings and, therefore, considered as one of the most effective and on-going fields of research. The main limitation of PCM is its leakage problem which limits its potential use in building construction and other applications such as TES and textiles, which can be overcome by employing nano-/micro-encapsulation technologies. This paper comprehensively overviews the nano-/micro-encapsulation technologies, which are mainly classified into three categories including physical, physiochemical and chemical methods, and the properties of microcapsules prepared. Among all encapsulation technologies available, the chemical method is commonly used since it offers the best technological approach in terms of encapsulation efficiency and better structural integrity of core material. There is a need to develop a method for the synthesis of nano-encapsulated PCMs to achieve enhanced structural stability and better fracture resistance and, thus, longer service life. The accumulated database of properties/performance of PCMs and synthesised nano-/micro-capsules from various techniques presented in the paper should serve as the most useful information for the production of nano-/micro-capsules with desirable characteristics for building construction application and further innovation of PCM technology.

In recent years the application of transformative technologies has, across a number of industries, represented a challenge to current industry paradigms, resulting in significant improvements in both technical capabilities and output efficiency, whilst disrupting established business models. Many industries are facing an uncertain future in which today’s technological limitations cannot be assumed to apply. The construction industry is likely to be significantly affected by potentially transformative technologies such as additive manufacturing (3D printing), artificial intelligence, and virtual/augmented reality. The application of such technologies presents both significant opportunities and challenges. There are a lot of bottlenecks that need to be resolved before we can maximize the positive impacts of transformative technologies on the construction industry. It is often claimed that additive manufacturing (AM) will transform the way we construct structures and buildings. Although, still in its infancy, this technology is likely to become an important part of the construction industry in relatively near future. AM as one of the most highlighted key enabling technologies has the potential to create disruptive solutions along with automation and robotics, that are at the forefront of building innovation. Material formulations and the science behind the interactions of different components undoubtedly counts as a vital workforce that determines the successful implementation of AM technology in the construction industry. There are fundamental interdependencies between the materials, the printing technologies, and both the scale and geometrical complexity of any printed structure. The construction industry can potentially take utmost advantage of the benefits of AM, e.g. improve safety, reduce labor and time, and advance customization. The key for successful development and implementation of AM is industry stakeholder collaboration involving materials science, architecture/design, computation, and robotics. Automation in construction will happen, there is no question about it and AM will have its role to a certain extent, as it cannot be the sole solution to major problems in the sector.

Vacuum Insulation Panels (VlP) are presently regarded as one of the most promising state-of-the-art building insulation solutions. Based on their thermal conductivities of about 4 mW/(m K), with a thickness below 40 mm, they have a great potential for near zero-energy buildings (nZEB) and for applications where high insulation standards and living space savings are crucial. However, VIP are still unaffordable for the majority of homeowners and contractors (up to 100 €/m 2 ), mostly due to the cost of the conventional fumed silica used as core material to secure the long service life requirements of building applications. This study presents the early developments of alternative cores engineered for VIP targeting the building market. The adopted strategy is to replace fumed silica with cheaper natural inorganic/organic lightweight materials or, alternatively, by creating multimaterial nanostructured composite matrices. The different compositions were analysed according to their physical, chemical and morphological characteristics and their respective thermal conductivity ranks. Promising lambda values as low as 5.3 mW/(m K) have been achieved for gas pressures below 10 mbar (1 kPa). It is expected that these novel core systems will be capable of suppressing the different heat transfer mechanisms at more reasonable costs than the current VIP fumed silica ones.

Additive manufacturing (AM) technologies have experienced a substantial growth in recent decades, AM technologies are able to fabricate and build complicated customized geometry composites without extra tools, and execute multi-materials manufacturing that conventional manufacturing methods cannot offer. This review investigated current AM technologies, including liquid, solid, powder and hybrid of liquid-powder based AM printings, and corresponding AM composites, including particle, nano-fillers and fibre reinforced AM composites. Full biocomposites of natural fibre-biopolymer for AM process have also been evaluated. Upon the understanding of all AM technologies, e.g. printing mechanisms, strength and weakness, and AM composite materials formulations, applicability and performance, the limitations and massive potentials of AM technologies and corresponding composites were discussed for further research, innovation and manufacturing.

This paper presents a comprehensive characterisation of wood flour geometry for polylactic acid (PLA) wood plastic composites (bioWPCs), and hence explores how the wood flour may influence the microstructure and performance of bioWPCs. The results show that current characterisation of wood flour from the literature can be misleading as they mostly rely on sieve analysis. Image analysis was used to critically study the fibres retained at various mesh sizes to investigate and examine the length and width distributions of the fibres prior to and after processing into bioWPCs. There were clear relationships between the reduction in both fibre size and aspect ratio and compounding processes depending on the original fibre geometry. It was also determined that by sieving out only the fibres retained at 500 µm much stronger bioWPCs can be produced than that using a single size fibre, achieving tensile and flexural stress of 15.3 and 13.2 MPa, respectively.

There has not been extensive research into the subjects of the interfacial bonding quality and the interaction mechanisms of biopolymers and natural fibres. Attempts have been made to incorporate natural fibres/fillers (biofibres) into the manufacture of composites in order to increase the functionality and performance of biopolymers synthesised from natural sources/microbial systems. However, the interfacial bonding quality and other substantial technical challenges still need to be addressed if their industrial use is to be realized. The interfacial bonding quality ultimately dictates the mechanical and physical performance of bio-composites. This review paper attempts to collate the state-of-the-art regarding coupling agents/ additives and their roles in interaction mechanisms with biofibres and biopolymers. Two potential pathways for narrowing the performance gap between biopolymer-based bio-composites and their petroleum-based counterparts are: i) improving the interfacial bonding quality by the synthesis of a specific coupling agent, and ii) improving the processability of bio-composites by blending two or more biopolymers.

Using expanded cork dust as a cheaper substitute of fumed silica, the expanded cork/fumed silica composites with hierarchical porous structure were designed and constructed as an alternative lower cost material for vacuum insulation panel (VIP) core. A novel strategy compromised of microwave pretreatment and vacuum impregnation method is developed for cork restructuring and recombination. The morphology, microstructure and thermo-physical properties of expanded cork/fumed silica composites were thoroughly investigated. It is found that the microwave pretreatment is a rapid and effective method to restructure cork, and then fumed silica can be introduced into the cork pores efficiently by the vacuum impregnation method, resulting in a hierarchical microstructure of cork micro-pores and nano-porous fumed silica micelle. Thanks to this unique hierarchical porous structure, the hybrid expanded cork-fumed silica materials show an excellent thermal insulation property (as low as 6.3 mW/m∙K at pressure < 1 mbar). The results demonstrate that the proposed strategy is an efficient means to construct a hierarchical porous expanded cork/fumed silica hybrid network system, and the as-prepared composites could have a potential application for VIPs core materials due its cost-effective and good thermal insulation performance. The research is supported by the European Union's Seventh Framework Program managed by REA-Research Executive Agency [FP7-SME-2013], under the GA No. 606037.