A Perspective on the Prowaste Concept: Efficient Utilization of Plastic Waste through Product Design and Process Innovation

This work is aimed to present an innovative technology for the reinforcement of beams for urban furniture, produced by in-mold extrusion of plastics from solid urban waste. This material, which is usually referred to as “recycled plastic lumber”, is characterized by very poor mechanical properties, which results in high deflections under flexural loads, particularly under creep conditions. The Prowaste project, founded by the EACI (European Agency for Competitiveness and Innovation) in the framework of the Eco-Innovation measure, was finalized to develop an innovative technology for selective reinforcement of recycled plastic lumber. Selective reinforcement was carried out by the addition of pultruded glass rods in specific positions with respect to the cross section of the beam, which allowed optimizing the reinforcing efficiency. The reinforcement of the plastic lumber beams with pultruded rods was tested at industrial scale plant, at Solteco SL (Alfaro, Spain). The beams obtained, characterized by low cost and weight, were commercialized by the Spanish company. The present paper presents the most relevant results of the Prowaste project. Initially, an evaluation of the different materials candidates for the reinforcement of recycled plastic lumber is presented. Plastic lumber beams produced in the industrial plant were characterized in terms of flexural properties. The results obtained are interpreted by means of beam theory, which allows for extrapolation of the characteristic features of beams produced by different reinforcing elements. Finally, a theoretical comparison with other approaches which can be used for the reinforcement of plastic lumber is presented, highlighting that, among others, the Prowaste concept maximizes the stiffening efficiency, allowing to significantly reduce the weight of the components.     

Physical Properties of an Eco-Sustainable,Form-Stable Phase Change Material Included in Aerial-Lime-Based Mortar Intended for Different Climates

The aim of this experimental investigation was to produce a form-stable phase change material (PCM) able to reduce the need for nonrenewable energy resources required for the heating/cooling of buildings located in regions characterized by different climatic conditions. The innovative PCM must also be sustainable and must be produced according to the principles of the circular economy. To achieve such ambitious goals, a form-stable, sustainable PCM was produced through vacuum impregnation. The form-stable PCM was produced starting from a low-toxicity, low-flammability polyethylene glycol of medium molecular weight (PEG 800), which was included in porous stone granules obtained as waste products of the cutting/processing of local (Lecce) stone. The thermal properties and thermal stability of PEG 800 and of its PCM-composite were evaluated by employing differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA). The appropriate parameters to perform the impregnation procedure were identified through rheological and calorimetric analyses. A simple leakage test was performed to assess if the PEG polymer can leak from the stone flakes. Finally, the new PCM was added as an aggregate in aerial-lime-based mortars, and the mortar’s properties were analyzed in fresh (workability) and hardened (flexural and compressive strength and thermal characteristics) states for potential applications, particularly in ancient buildings.     

Cold-Curing Structural Epoxy Resins: Analysis of the Curing Reaction as a Function of Curing Time and Thickness

The curing reaction of a commercial cold-curing structural epoxy resin, specifically formulated for civil engineering applications, was analyzed by thermal analysis as a function of the curing time and the sample thickness. Original and remarkable results regarding the effects of curing time on the glass transition temperature and on the residual heat of reaction of the cold-cured epoxy were obtained. The influence of the sample thickness on the curing reaction of the cold-cured resin was also deeply investigated. A highly exothermal reaction, based on a self-activated frontal polymerization reaction, was supposed and verified trough a suitable temperature signal acquisition system, specifically realized for this measurement. This is one of the first studies carried out on the curing behavior of these peculiar cold-cured epoxy resins as a function of curing time and thickness.     

Microgel Modified UV-Cured Methacrylic-Silica Hybrid: Synthesis and Characterization

An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was firstly carried out. The O-I hybrid first proposed in this study was obtained from organic precursors with a high siloxane content, which are mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silica nanodomains dispersed within the crosslinked organic phase, as a result of the sol-gel process. The first part of the research deals with the selection and optimization of suitable systems through appropriate chemical modifications, in order to ensure that curing reactions can be carried out at room temperature and in the presence of UV radiation. Firstly, the silica domains are formed, followed by crosslinking reactions of the acrylic groups in the oligomer via a free radical polymerization. The crosslinking reaction was controlled with the use of a suitable photoinitiator. Most of the experimental work was devoted to understanding the morphology of the hybrid system, both in uncured and cured states, and to assess its final thermal and optical properties, using different experiential techniques.     

Adhesive Joint Degradation Due to Hardener-to-Epoxy Ratio Inaccuracy under Varying Curing and Thermal Operating Conditions

This paper presents the results of an experimental study of adhesive joint strength with consideration of the inaccuracy of the hardener dosage, in the context of evaluating the degradation of joints when used either at ambient or elevated temperatures. The butt joint strength characteristics were assessed for two types of adhesives—rigid and flexible—and two curing scenarios—with and without heat curing. An excess hardener was shown to be significantly more unfavourable than its deficiency, which can ultimately be considered as a recommendation for forming epoxy adhesive joint assemblies. In order to fully understand the relationship between the analysed mechanical properties of the material and the influence of component ratio excesses and heating, a process of fitting basic mathematical models to the obtained experimental data was also performed.     

Cold-Cured Bisphenolic Epoxy Adhesive Filled with Low Amounts of CaCO3: Effect of the Filler on the Durability to Aqueous Environments

The effects of aging exposures to three non-saline aqueous environments on the compressive mechanical properties of a calcium carbonate-filled bisphenolic epoxy adhesive, cold-cured with the addition of two curing agents suitable for the cure at ambient temperature (i.e., Mannich base and triethylenetetramine), were assessed. The amount of the added filler (CaCO₃) varied from 1 to 3 g per 100 g of resin; the immersion times in each of the selected medium varied from 1 to 10 months. It was found that the mechanical properties measured in compression mode on cylindrical specimens of unfilled and CaCO₃-loaded epoxy were scarcely influenced by the kind of curing agent employed; only the compressive modulus was limitedly affected by this parameter. Referring to the behavior when aged in water, the CaCO₃-filled epoxies displayed noticeable growths in modulus, small reductions in strength, and limited variations in strain, with a certain influence of the exposure time, especially when comparing the properties at the lowest time with those at medium–long times. On the basis of the results of statistical MANOVA analysis, it can be concluded that among the compositional factors (i.e., the type of curing agent employed to cure the epoxy compounds and the micro-filler content), only the amount of CaCO₃ filler significantly affects the compressive modulus.     

Physical Properties of Eco-Sustainable Form-Stable Phase Change Materials Included in Mortars Suitable for Buildings Located in Different Continental Regions

Starting from two low-cost, low-environmental-impact polymers belonging to the Polyethylene Glycol (PEG) family, i.e., PEG 800 and PEG 1000, two form-stable phase change materials were produced. The two PEGs differ in molecular weight and, as a consequence, the melting and crystallization range of temperatures. The PCMs were obtained, including the PEG, in a liquid state, inside the pores of Lecce Stone flakes, obtained as waste pieces from its processing. A simple and inexpensive impregnation process was selected to produce the PCMs, thus adopting low-environmental-impact materials and cheap processes, and respecting circular economy principles. The two PCMs, the first composed of PEG 800, namely LS/PEG800, and the second composed of a 50/50%wt. mix of the different LS/PEGs, i.e., LS/PEG800_LS/PEG1000, were added as aggregates to four types of mortars, based on aerial and hydraulic lime, gypsum, and cement. The obtained mortars were characterized in their fresh state to assess their workability, and in a solid state after a proper cure to determine their characteristic Latent Heat Thermal Energy Storage (LHTES) properties and mechanical properties in both flexural and compressive modes, taking the mortars not containing any PCM as the reference. The results revealed that, with the proper selection of mortar formulations, it was possible to achieve suitable workability and adequate mechanical characteristics. The selection of a PEG with a low range of phase change temperatures, such as PEG 800, allows one to obtain mortars characterized by a melting/crystallization range that can be considered appropriate in applications characterized by cold climates. The production of a mixed PCM, composed of both PEGs, led to mortars displaying a large interval of melting/crystallization temperatures, which could be suitable in both warm and cold climates.     

Characterization of Nanocomposites by Thermal Analysis

In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.