Miguel Rodríguez-Pérez

• Doctor of Philosophy
• Professor (Full) at University of Valladolid

In this study, the relationship between the porous structure of polylactic acid-based (PLA) aerogels and their thermal insulation performance have been studied in detail. Different polymer contents were used for the fabrication of these aerogels leading to a wide range of low densities (36–167 kg/m3), porosities over 86 % and high crystallinity deg...

The structural characterization is an essential task in the study of porous materials. To achieve reliable results, it requires to evaluate images with hundreds of pores. Current methods require large time amounts and are subjected to human errors and subjectivity. A completely automatic tool would not only speed up the process but also enhance its...

The viscoelastic properties development during the reactive foaming of four standard polyurethane formulations was monitored using a flooded parallel plate rheometer. The measurements in situ demonstrated how foams of low catalyst content took longer than 10 min to increase their viscosity from 1 to 10³ Pa s, while foams with higher catalysts reach...

The aerogel performance for industrial uses can be tailored using several chemical and physical strategies. The effects of a controlled densification on polyurethane aerogels are herein studied by analyzing their textural, mechanical, sound, optical, and thermal insulating properties. The produced aerogels are uniaxially compressed to different str...

The global plastic consumption, as one of the paramount concerns of our society, opens new paths of investigation in green materials. This study presents contribution to the field with the obtention of natural rubber latex foams (NRLF using egg white powder (EW) as the biostabilizing agent. The route followed to develop these samples is based on a...

In this study, a novel application of synchrotron X-ray nanotomography based on high-resolution full-field transmission X-ray microscopy for characterizing the structure and morphology of micrometric hollow polymeric fibers is presented. By employing postimage analysis using an open-source software such as Tomviz and ImageJ, various key parameters...

This article studies the effect of adding different contents of surface-modified multiwalled carbon nanotubes (CNTs) on the structure and final properties of polyisocyanurate-polyurethane aerogels. The produced samples were characterized in terms of density, porosity, shrinkage, textural properties, mechanical behavior, ultrasonic behavior, and the...

The growing popularity of silver nanoparticles in the field of nanotechnology has created the necessity of developing new sustainable synthesis methods. This study presents a new green in situ functionalization method of melamine foams with silver nanoparticles. The synthesis pathway and the influence of the processing parameters are optimized to p...

Polyisocyanurate (PIR) foam is a thermal insulating material widely used in many industries such as construction, refrigeration, piping/tubing among others. In this research the production, characterization and modeling of the thermal conductivity of PIR foams synthesized with a hydrofluorolefin (HFO 1233zd (E)) as physical foaming agent have been...

A new approach to produce porous membranes with dense or porous top layer is proposed in this work by employing a solvent-free method. PMMA/MAM formulations were selected as a base material in order to create open-cell or close-cell structures by gas dissolution foaming employing CO2 as a blowing agent. Furthermore, by introducing the gas diffusion...

As additive manufacturing (AM) becomes more widespread in ever more demanding applications, the performance demands on printed parts are increasing. Efforts are directed towards improving mechanical performance in all manufacturing directions, including requirements such as sustainability, economic viability, and weight savings. This work focuses o...

The production of open‐cell (OC) nanostructures in polymer foams without non‐foamed solid skins by gas dissolution foaming has been developed in this work. First, several grades of MAM block copolymer (methyl methacrylate‐ b ‐butyl acrylate‐ b ‐methyl methacrylate) at high content are employed as heterogeneous phase in poly(methyl methacrylate) for...

The excellent catalytic properties of copper nano-particles (CuNPs) for the degradation of the highly toxic and recalcitrant chlorpyrifos pesticide are widely known. However, CuNPs generally present low stability caused by their high sensitivity to oxidation, which leads to a change of the catalytic response over time. In the current work, the immo...

Silica-based aerogels have been successfully reinforced by means of reticulated polymeric polyurethane (PU) foams with different cell sizes. The resultant silica aerogel-PU foam composites (Sil-PU composites) were fully characterized (density, shrinkage, aerogel percentage, and porous structure), and the mechanical properties and thermal conductivi...

This work shows a route to reduce the thermal conductivity of nanocellular poly(methyl-methacrylate) (PMMA). This approach is based on micronizing to replace the continuous solid phase by a discontinuous one. PMMA powders with densities of 147–195 kg/m3, formed by particles of 100 microns with nanometric cells inside them, are produced by milling....

The characterization of the thermal conductivity of new and enhanced thermal insulators developed at lab-scale is a challenge. The small dimensions of the prototypes make impossible the use of the conventional techniques because steady-state methods require large samples. Furthermore, the accuracy of transient methods to measure the thermal conduct...

LDPE (low-density polyethylene) foams were prepared using the improved compression moulding technique (ICM) with relative densities ranging from 0.3 to 0.7 and with different levels of chemical blowing agents (from 1% to 20%). The density gradients, cellular structure and thermal conductivity of the foams were characterized. The density and amount...

A family of transparent polyisocyanurate-polyurethane (PUR-PIR) aerogels with an interesting combination of physical properties were synthesized. First, their textural properties were analyzed aiming to study catalyst influence on the final porous structures and densities. Their thermal conductivities were measured at different temperatures allowin...

Nowadays, developing advanced, highly insulating materials for minimizing heat losses in buildings is of utmost relevance. Thus, there is a constant research activity focused on developing new and enhanced solutions for thermal insulation. However, characterizing the behavior of new thermal insulation materials, usually produced at lab-scale with s...

The incorporation of silica aerogel particles into the isocyanate used to prepare Rigid Polyurethane composite foams drastically modifies its rheological behaviour. The isocyanate changes from being a Newtonian fluid of constant viscosity (0.3 Pa s at 25 °C) to a non-linear power-law material with complex viscosity decreasing from 10⁴ to 10¹ Pa s w...

Nowadays, finding new materials with enhanced thermal insulation properties has become a mandatory task to reduce energy consumption and CO2 emissions. In recent years, nanocellular polymers have aroused great attention due to their very interesting combination of properties, which include reduced conduction through the gas phase thanks to the Knud...

A novel synthesis of polyurethane foam/polyurethane aerogel (PUF–PUA) composites is presented. Three different polyurethane reticulated foams which present the same density but different pore sizes (named S for small, M for medium, and L for large) have been used. After the characterization of the reference materials (either, foams, and pure aeroge...

Nowadays, our society is facing problems related to energy availability. Owing to the energy savings that insulators provide, the search for effective insulating materials is a focus of interest. Since the current insulators do not meet the increasingly strict requirements, developing materials with a greater insulating capacity is needed. Until no...

In this work, silica aerogel composites reinforced with reticulated polyurethane (PU) foams have been manufactured having densities in the range from 117 to 266 kg/m³ and porosities between 85.7 and 92.3%. Two different drying processes were employed (ambient pressure drying and supercritical drying) and a surface modification step was applied to s...

Highly transparent polyisocyanurate–polyurethane (PUR–PIR) aerogels were synthesized, and their optical properties were studied in detail. After determining the density and structural parameters of the manufactured materials, we analyzed their optical transmittance. It was demonstrated that the catalyst content used to produce the aerogels can be e...

Polyurethane foams with a hybrid structure between closed cell and open cell were fabricated and fully characterized. Sound absorption measurements were carried out in order to assess their acoustic performance at different frequency ranges. The cellular structure of these systems was studied in detail by defining some novel structural parameters t...

In this study, we investigated the influence of mixing conditions on the foaming process of water blown polyurethane (PU) foams obtained at different mixing speeds (50, 500, 1000 and 2000 rpm). In particular, the morphological evolution during the foaming process, in terms of the bubble size and bubble density, was studied via optical observations,...

The use of metal-organic frameworks (MOF) nanoparticles as nucleating agents in gas dissolution foaming processes is presented. In this work, MOF nanoparticles with three different particle sizes were synthetized and introduced in film composites based on polystyrene at 1 wt.%. The addition of nanoparticles with high affinity to CO 2 , which is the...

An innovative approach to reduce and eliminate the non-foamed solid skins of the cellular polymers fabricated by gas dissolution foaming is presented in this work. The incorporation of a flexible gas diffusion barrier on the polymer surfaces during the saturation and foaming processes provided significant reduction or even hindered the appearance o...

Among the different strategies to improve cellular polymers’ performance, a very promising approach is reducing the cell size to the nano-scale, that is, the development of nanocellular polymers or nanocellular foams. These materials, characterized by cell sizes from tens to hundreds of nanometers, have aroused great interest in the polymer foam re...

Three independent analysis methods were developed to investigate the distribution of solid mass in foams analyzed by X-ray tomography with effective pixel sizes larger than the thickness of the solid network (sub-pixel conditions). Validation of the methods was achieved by a comparison with the results obtained employing high-resolution tomography...

In the present study, a promising flame retardant consisting of 80 wt% silane-modified nanosepiolites functionalized with 20 wt% graphite (SFG) is used to obtain a synergistic effect principally focussed on the thermal stability of water-blown rigid polyurethane (RPU) foams. Density, microcellular structure, thermal stability and thermal conductivi...

Different percentages of an elastomeric phase of styrene-ethylene-butylene-styrene (SEBS) were added to a polystyrene (PS) matrix to evaluate its nucleating effect in PS foams. It has been demonstrated that a minimum quantity of SEBS produces a high nucleation effect on the cellular materials that are produced. In particular, the results show that...

The key parameters and production route for the easy production of highly transparent nanocellular films based on polymethyl methacrylate (PMMA) with thickness below 1 mm are herein described. The use of the gas dissolution foaming process (CO2 as physical blowing agent) with saturation pressures of 40 and 50 MPa, a saturation temperature of 0 °C a...

Polycarbonate (PC) is a widely used engineering thermoplastic. Also, bead foaming technology is a method to produce high-performance, low-density foams with complex geometries. In this work, expanded polycarbonate (EPC) with microcellullar structure and low density have been produced for the first time using the autoclave bead foaming technique. Th...

A series of thermoplastic polyurethanes (TPUs) with different amounts of hard segments (HS) (40, 50 and 60 wt.%) are synthesized by a pre-polymer method. These synthesized TPUs are characterized by Shore hardness, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), dynamic mechanical th...

Transparent polyurethane aerogels with ultralow densities and high porosities have been synthesized for the first time. The effect of five different catalyst amounts on the final properties of the aerogels is analyzed. It has been found that increasing the catalyst amount leads to higher porosities and larger particles sizes. This structure has bee...

Nanocomposite polymers and, in particular, nanocomposite polymer foams have been proposed in the last years as efficient materials for wastewater remediation. The main advantage of this approach is that it prevents accidental liberation of the active nanoparticles to the environment and facilitates the handling during the remediation operations. Ho...

In this work, the effects of thermoplastic polyurethane (TPU) chemistry and concentration on the cellular structure of nanocellular polymers based on poly(methyl-methacrylate) (PMMA) are presented. Three grades of TPU with different fractions of hard segments (HS) (60%, 70%, and 80%) have been synthesized by the prepolymer method. Nanocellular poly...

The modulus build-up and relative density evolution during the reactive foaming of four standard polyurethane formulations was monitored in-situ by Dynamic Mechanical Analysis (DMA) with a customised set-up in parallel plate geometry. The modulus increased from 0.01 MPa in the first minutes to over 1.2 MPa within 20 min. The set-up also enabled the...

The main objective of this work is to analyze how the cellular structure of foamed polystyrene based (PS) nanocomposites, produced by gas dissolution foaming, is affected by the extensional rheological behavior of the polymer matrix and by the dispersion degree of the particles. These composites have been produced with different types of natural an...

To determine the effect of nanoclays and trapped air on the formation of rigid polyurethane foams, three different production procedures were used. To study the influence of mixing at atmospheric pressure, two approaches were carried out employing either an electric or a magnetic stirrer. The third approach was executed by mixing under vacuum condi...

The effect of the catalyst concentration on the synthesis and textural properties of polyisocyanurate-polyurethane aerogels is analyzed. The use of different catalyst amounts allows obtaining low-density aerogels (0.10−0.16 g/cm 3) with high porosities (85−91%). Their porous structures were analyzed by scanning electron microscopy and nitrogen adso...

A new approach to produce nanocellular polymers combining small cell sizes with low relative densities is presented herein. This production method, based on gas dissolution foaming, consists of performing a double saturation and foaming cycle. Thus, nanocellular polymethylmethacrylate (PMMA) has been produced through a first saturation at different...

In the present work blends of polystyrene (PS) with sepiolites have been produced using a melt extrusion process. The dispersion degree of the sepiolites in the PS has been analyzed by dynamic shear rheology and X‐ray micro‐computed tomography. Sepiolites treated with quaternary ammonium salts (O‐QASEP) are better dispersed in the PS matrix than na...

A portable potentiometric electronic tongue (PE-tongue) was developed and applied to evaluate the quality of milk with different fat content (skimmed, semi-skimmed, and whole) and with different nutritional content (classic, calcium-enriched, lactose-free, folic acid–enriched, and enriched in sterols of vegetal origin). The system consisted of a si...

A novel set-up for monitoring the gas diffusion process in polymers has been developed. This set-up is based on performing neutron radiography and tomography of polymeric materials under high pressures of gas. Information about the absorption kinetics of supercritical CO2 was obtained. Additionally, solubility, diffusivity, and macroscopic changes...

The kinetics of crystallization of Polylactic Acid (PLA) in the presence of CO2 pressures from 1.5 to 4 MPa, has been studied by measuring the optical absorbance evolution of the material with time. To perform this study, an own-designed pressure vessel provided with windows has been used. The non-destructive approach presented in this paper allows...

Glass foams are highly sustainable materials with enormous potential to replace traditional thermal insulators. Current research on glass foams is focused on improving thermal insulation by reducing density, but this is somehow a limited approach. Selecting the best approach to reduce thermal conductivity relies on establishing a detailed knowledge...

Different blends of a linear polypropylene (L‐PP), a long‐chain branched polypropylene (LCB‐PP), and a polyolefin elastomer (POE) are prepared and foamed using core‐back injection molding. The objective is to analyze the use of POE and LCB‐PP as complementary strategies to improve cellular polymers’ impact response. Different parameters are then st...

The impact resistance of injection‐molded polypropylene (PP) parts is severely reduced when they are foamed. It is necessary to implement strategies, such as elastomer toughening, to increase the impact behavior of foamed parts. However, the knowledge on the effect of elastomer addition on the morphology, cellular structure, and impact of injection...

The physical behavior of polymethyl methacrylate-carbon dioxide (PMMA-CO2) system was studied in a wide range of temperatures (0 to 100 °C) and pressures (0.1 to 10 MPa). The glass transition temperature of the systems was determined by a new optical observation methodology. The developed procedure is based on the refraction index variations betwee...

Among the various mechanisms playing a role in the heat transfer through nanocellular polymers, the radiation contribution remains the most unknown, since there is a lack of experimental data about how infrared light interacts with such structures. In this work, we present the first experimental measurements of the transmittance in the infrared reg...

This study mainly concerns the role of foam heating process techniques and its impact on cellular micromorphology, density and gas liberation mechanism of natural rubber foam with distilled water as blowing agent. Three different modes of heating process techniques and varying amount of distilled water have been examined on the foam density and cel...

A new and straightforward route to produce polymeric hollow microfibers is proposed. Polycaprolactone (PCL) hollow fibers are obtained for the first time by an environmentally friendly gas dissolution foaming approach, overcoming its limitations to induce porosity on samples on the micrometric range. Different porous morphologies are achieved from...

Nanocellular polymethylmethacrylate (PMMA) is produced through a newly proposed method, a two‐stage depressurization in the gas dissolution foaming process. This method modifies the depressurization step and allows controlling the pressure during cell growth, avoiding this way, the appearance of micrometric defects in the produced cellular material...

Water blown rigid polyurethane (RPU) composite foams were produced using different concentrations of nanoporous silica aerogel micrometric powder (0.5, 1 and 3 wt%). The effect of these particles on the foaming kinetics was analysed from a physical and chemical viewpoint. On the physical side, the foaming process was studied by in-situ X-ray radios...

Future developments in foamed glass should focus on improving the thermal insulation properties, controlling the foamed structure and the type of porosity. In this study, we report on the synthesis and properties of foamed glasses with open-porous and closed-porous structures prepared from waste cathode-ray-tube (CRT) panel and soda-lime-silica gla...

In this work, rigid polyurethane foams (RPUF) were flame retarded by adding 8 wt % expandable graphite (EG) and EG/Phenylphosphonic-aniline salt (FR1) flame retardant compounds. The adding amount of EG/FR1 compound is 8 wt % as well, and different ratios (8:1 and 12:1) of EG to FR1 were designed. Detailed characterizations of the density, cellular...

Nanocomposite hydrophilic flexible polyurethane foams were prepared by in situ polymerization using an organomodified sepiolite as filler. The sepiolite affinity by nitrates dissolved in water was increased by treating them with quaternary ammonium salts (S-QAS), leading to remarkable nitrates maximum adsorption capacity (qmax = 23.30 mg/g). The La...

The use of polymeric nanocomposites has arisen as a promising solution to take advantage of the properties of nanoparticles (NPs) in diverse applications (e.g., water treatment, catalysis), while overcoming the drawbacks of free-standing nanoparticles (e.g., aggregation or accidental release). In most of the cases, the amount and size of the NPs wi...

In this work, formulations based on composites of a linear polypropylene (L-PP), a long-chain branched polypropylene (LCB-PP), a polypropylene–graft–maleic anhydride (PP-MA), a styrene-ethylene-butylene-styrene copolymer (SEBS), glass fibers (GF), and halloysite nanotubes (HNT-QM) have been foamed by using the improved compression molding route (IC...

The cover image is based on the Research Article Influence of the viscosity of PMMA on the cellular structure of nanocellular materials by Judith Martín‐de Leí;n et al., DOI: 10.1002/pi.5920. Cover credit: Cover image ©Judith Martín‐de León Images

Three different grades of poly(methyl methacrylate) (PMMA) with different rheological properties are used for the production of nanocellular materials using gas dissolution foaming. The influences of both the viscosity of the different polymers and the processing parameters on the final cellular structure are studied using a wide range of saturatio...

The devastating effects of oil spills on the ecosystems must be minimized by looking for effective solutions which offer a fast response to them. This work aimed at characterizing the oil-absorption capacity of flexible low-density open-cell foams based on polyolefins with different levels of tortuosity by comparing it to the one displayed by a com...

Voltametric sensors formed by the combination of a sulfur-substituted zinc phthalocyanine (ZnPcRS) and gold nanoparticles capped with tetraoctylammonium bromide (AuNPtOcBr) have been developed. The influence of the nature of the interaction between both components in the response towards catechol has been evaluated. Electrodes modified with a mixtu...

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low‐density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the proc...

Solid-state nanofoaming experiments are conducted on two polymethyl methacrylate (PMMA) grades of markedly different molecular weight using CO2 as the blowing agent. The sensitivity of porosity to foaming time and foaming temperature is measured. Also, the microstructure of the PMMA nanofoams is characterized in terms of cell size and cell nucleati...

An important water pollution problem is caused by nitrogen containing compounds. Specifically, the toxicity of nitrates (NO3-) to humans is mainly attributable to a reduction of the oxygen transport to the tissues, called methemoglobinemia, which affects principally to infants under 3 months of age. The main objective of this research is to develo...

Solid-state nanofoaming experiments are conducted on two PMMA grades of markedly different molecular weight using CO$_2$ as the blowing agent. The sensitivity of porosity to foaming time and foaming temperature is measured. Also, the microstructure of the PMMA nanofoams is characterised in terms of cell size and cell nucleation density. A one dimen...

This paper describes the mechanical behavior in compression, at both low‐ and high‐strain rates, of several low‐density open‐cell polyolefin‐based foams with different gas phase interconnectivities and different levels of gas‐phase tortuosity. The mechanical properties of the open‐cell polyolefin foams have been compared with two different referenc...

Solid-state foaming experiments are conducted on three grades of polymethyl methacrylate (PMMA). Nanocellular PMMA foams are manufactured with an average cell size ranging from 20 nm to 84 nm and a relative density between 0.37 and 0.5. For benchmarking purposes, additional microcellular PMMA foams with an average cell size close to 1 μm and relati...

An understanding of the long‐term thermal conductivity of rigid polyurethane (RPU) foams presents great interest in the building field considering the conservation of energy efficiency. In this study, the effect of different types of particles (talc, diatomaceous earth and non‐porous silica) on the thermal conductivity of RPU foams blown with cyclo...

Nanocellular polymers are novel materials characterized by nanometric cell sizes with huge potential in many industrial applications. However, their production is challenging and usually requires demanding processing conditions that make difficult the production at industrial scale. In this work, we prove that nanocellular polymers based on PMMA ca...

One strategy to produce nanocellular polymers is the use of nucleating species to promote nucleation. Whereas two-phase systems are widely studied, tri-phasic blends with two nucleating agents are uncommonly investigated. In this work, nanocellular polymers are obtained using tri-phasic blends of polymethylmethacrylate (PMMA) with two nucleating ag...

This paper presents a new methodology based on gas chromatography-mass spectrometry (GCMS) in order to separate and quantify the gases presented inside the cells of rigid polyurethane (RPU) foams. To demonstrate this novel methodology, the gas composition along more than three years of aging is herein determined for two samples: a reference foam an...

Bimodal cellular poly(methyl methacrylate) with micron and nano sized (300 to 500 nm) cells with up to 5 weight percent of sepiolite nanoparticles and porosity from 50 weight percent to 75 weight percent are produced by solid state foaming. Uniaxial compression tests are performed to measure the effect of sepiolite concentration on the elastic modu...

In this work, the cellular structure, physical properties, and the structure–property relationship of several novel crosslinked ethylene butyl acrylate (EBA) foams with different cellular structure interconnectivity (low tortuosity and high tortuosity) have been analyzed and compared to that of closed cell EBA foams and to that of an open‐cell poly...

The cover image is based on the Research Article Anisotropy in nanocellular polymers promoted by the addition of needle‐like sepiolites by Victoria Bernardo et al. DOI: 10.1002/pi.5813.