Rigid Foam Research Articles

Behavior Characteristics and Thermal Energy Absorption Mechanism of Physical Blowing Agents in Polyurethane Foaming Process.

Polyurethane rigid foam is a widely used insulation material, and the behavior characteristics and heat absorption performance of the blowing agent used in the foaming process are key factors that affect the molding performance of this material. In this work, the behavior characteristics and heat absorption of the polyurethane physical blowing agent in the foaming process were studied; this is something which has not been comprehensively studied before. This study investigated the behavior characteristics of polyurethane physical blowing agents in the same formulation system, including the efficiency, dissolution, and loss rates of the physical blowing agents during the polyurethane foaming process. The research findings indicate that both the physical blowing agent mass efficiency rate and mass dissolution rate are influenced by the vaporization and condensation process of physical blowing agent. For the same type of physical blowing agent, the amount of heat absorbed per unit mass decreases gradually as the quantity of physical blowing agent increases. The relationship between the two shows a pattern of initial rapid decrease followed by a slower decrease. Under the same physical blowing agent content, the higher the heat absorbed per unit mass of physical blowing agent, the lower the internal temperature of the foam when the foam stops expanding. The heat absorbed per unit mass of the physical blowing agents is a key factor affecting the internal temperature of the foam when it stops expanding. From the perspective of heat control of the polyurethane reaction system, the effects of physical blowing agents on the foam quality were ranked in order from good to poor as follows: HFC-245fa, HFC-365mfc, HFCO-1233zd(E), HFO-1336mzzZ, and HCFC-141b.

Applicability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) bark extract as a precursor of rigid carbon foam and activated carbon

Hybrid aspens have long attracted scientific interest, but the research on their use as feedstocks for chemical applications are still very limited. The bark biomass of the poplar species contains many valuable extractives that can be utilized as value-added products. This paper examines the applicability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) bark extract as a precursor of rigid carbon foam and activated carbon. To explore this, the study considers 1) the basic chemical composition of the bark in terms of added value potential, 2) the basic chemical composition of the bark extract and the effect of its pretreatment on the extract composition, 3) the production of rigid carbon foam, and 4) the chemical activation of carbon foam with different impregnating agents. The study determines that the bark extract of the hybrid aspen can be used as a precursor for rigid carbon foam and further processed into an activated carbon product. Therefore, the bark extract of Populus tremula L. × P. tremuloides Michx. can be assessed as a potential value-added product that increases the use value of the hybrid aspen biomass.

Effect of Crosslink Density on Thermal Aging of Bio-Based Rigid Low-Density Closed-Cell Polyurethane Foams

Gradual replacement of the traditional raw materials in polyurethane (PU) synthesis by bio-based ones and introduction of environmentally friendly physical blowing agents (PBAs) motivate the analysis of thermal aging of bio-based foams in order to optimize the chemical structure of the PU matrix so that its permeability to PBA is minimized. With the aim of elucidating the effect of the PU chemical structure on thermal aging of foams, rigid low-density closed-cell PU foams were produced solely from bio-based polyols. The effective diffusivities of PBA and atmospheric gasses were evaluated based on the measured thermal conductivity aging of foams and validated by gas chromatography measurements of gas composition in foam cells. Gas permeability of the PU polymer was estimated based on effective diffusivity in foams and foam morphology and found to decrease with increasing crosslink density, apparently due to reduction in the fractional free volume in the polymers.

Changes and Trends-Efficiency of Physical Blowing Agents in Polyurethane Foam Materials.

This work developed a novel method for measuring the effective rate of a PBA (physical blowing agent) and solved the problem that the effective rate of a PBA could not be directly measured or calculated in previous studies. The results show that the effectiveness of different PBAs under the same experimental conditions varied widely, from approximately 50% to almost 90%. In this study, the overall average effective rates of the PBAs HFC-245fa, HFO-1336mzzZ, HFC-365mfc, HFCO-1233zd(E), and HCFC-141b are in descending order. In all experimental groups, the relationship between the effective rate of the PBA, rePBA, and the initial mass ratio of the PBA to other blending materials in the polyurethane rigid foam, w, demonstrated a trend of first decreasing and then gradually stabilizing or slightly increasing. This trend is caused by the interaction of PBA molecules among themselves and with other component molecules in the foamed material and the temperature of the foaming system. In general, the influence of system temperature dominated when w was less than 9.05 wt%, and the interaction of PBA molecules among themselves and with other component molecules in the foamed material dominated when w was greater than 9.05 wt%. The effective rate of the PBA is also related to the states of gasification and condensation when they reach equilibrium. The properties of the PBA itself determine the overall efficiency, while the balance between the gasification and condensation processes of the PBA further leads to a regular change in efficiency with respect to w around the overall average level.

Influence of specimen size and density variation in the foam rise direction on the compressive behavior of PVC foams

Mechanical properties governing the localized deformation mechanisms, apparent elastic modulus and their correlation to specimen geometry in polymeric foams are important phenomena that are not well understood. Despite the well-studied density variation in Functionally Graded Foams (FGF), density variation in the foam rise direction of conventional foams has not received adequate attention in the current literature. The influence of specimen size and density variation on the deformation mechanisms and mechanical properties observed in the rise direction of H-series rigid PVC foams were experimentally investigated in this study by considering four distinct specimen sizes and five nominal densities. PVC foams with different nominal densities exhibited various density variation patterns, in a range of 2.6–26.3 % variation, in the foam rise direction which were found to govern the polymeric foams’ localized deformation mechanisms and the post-yield stress drop-off behavior. The plateau stress was observed as most sensitive to the foam density; specimens with higher densities exhibited up to 19 % higher plateau stress within the foam panel with a 200 kg/m3 nominal density. While specimen thickness significantly influenced the loading elastic modulus. Intermittent unloading-reloading cycle testing was conducted on thick and thin specimens to characterize the influence of specimen thickness on the apparent elastic modulus. The influence of thickness on the unloading elastic modulus was negligible, for example, reducing the specimen thickness from 25.40 mm to 6.35 mm decreased the loading and unloading elastic moduli by 39 % and 7 %, respectively, for PVC foams with a nominal density of 200 kg/m3. Therefore, the unloading elastic modulus should be utilized in future studies for more accurate cross-comparison between the mechanical properties of specimens with significantly different thicknesses.

Preparation and Characterization of Polyurethane Rigid Foam Nanocomposites from Used Cooking Oil and Perlite

Modern chemical industries trend towards industrial ecology to achieve a circular economy, because of increasing environmental and economic awareness jointly. One of the most important of these industries is polyurethane, accompanied by more and more interest in using renewable polyols. The study focuses on synthesizing and characterizing polyurethane rigid foams formulated by replacing 40%, 60%, and 100% of a petrochemical polyol with a bio-polyol derived from used cooking oil, and introducing perlite and modified perlite nanoparticles into the bio-polyol. The products were evidenced by transmission electron microscopy (TEM), Fourier transform infrared (FTIR), nuclear magnetic resonance spectral analyses, thermogravimetric analysis (TGA), and scanning electron microscopy equipped with energy-dispersive spectroscopy. The results indicate that the hydroxide value and viscosity at 25°C of the bio-polyol were around 456 ± 30 mg KOH/g and 148 mPa s. Bio-polyol blends of 40% and 60% had no significant effect on the thermal properties of polyurethane systems. The lowest value of char yield was observed for the sample with a 100% bio-polyol content of 2.3%. The beneficial effects of both perlite and modified perlite particles on the 100% bio-polyol-based foam were observed as having an effective role in improving thermal stability and reconstructing cellular structure. The yield char increased to 13.2%, 14%, 14.7%, and 15% for the two filler contents 2.5% and 5%. However, the new bio-polyol has a fairly good value in industrial construction, and the perlite particles have enhanced and improved this value.

Shear Transfer Mechanism between CFRP Grid and EPS Rigid Foam Insulation of Precast Concrete Sandwich Panels

An experimental program was implemented to investigate the shear transfer mechanism of carbon-fiber-reinforced polymer (CFRP) grids and expanded polystyrene (EPS) rigid foam insulation in three wythe precast concrete sandwich wall panels. The purpose of the research was to measure the shear flow capacity and to observe the failure mode(s) of precast concrete sandwich panels manufactured with a CFRP grid shear transfer mechanism between wythes. Six precast concrete sandwich panels were examined by push-out tests in which the center concrete wythe was pushed downward with respect to two outer concrete wythes. It was observed that the average shear flow capacity of the specimens having 2 in (51 mm) thick foam was higher than that of the specimens having 4 in (102 mm) thick foam. In addition, stiffness decreased significantly when the thickness of the EPS insulation increased. The failure mode for the panels included relative displacement between the center concrete wythe and the outer concrete wythes. Test results showed that panels tended to fail by CFRP grid rupture, CFRP grid pull-out, and loss of bond at the concrete/foam interface. Further tests should be performed to fully comprehend the nature of the shear transfer mechanism between the specific CFRP grid used and EPS rigid foam insulation.

A novel strategy inspired by steaming Chinese steamed bread for preparation of tannin-furanic rigid bio-foam

Tannin-furanic rigid foam material has been receiving extensive attention due to its renewable, easy-preparation, lightweight, thermal insulation, and flame retardancy, that been considering a potential flame-retardants and thermally-insulating materials in construction field. The most fashionable approaches for tannin-furanic foam manufacturing, currently, are the self-blowing expansion with the aid of blowing agent with/without extra heating, and foaming via mechanical stirring in presence of non-environmentally friendly crosslinker. Herein, a novel and green strategy was proposed for tannin-furanic rigid foam preparation without blowing agent and additional crosslinker by steam-driven foaming. The performance of steam-driven tannin-furanic based foam (SDTF) was evaluated systematically and a possible foaming mechanism was suggested. The results indicated that a totally different surface but similar microstructure morphology of SDTF was developed, which displayed a larger cell size and thicker cell wall than standard tannin-furanic-formaldehyde foam (STF). A much lower pulverization ratio (approximately 4.6%) was reached for SDTF with respect to STF even though its compression strength was only less than half. An excellent thermal insulation performance was verified by the thermal conductivity of SDTF, only approximately 0.0286 W/m·K, which is considered ultra-low value that the STF cannot reach or seldom reach after STF modification or/and special structure design. The flame retardancy of SDTF was investigated by LOI and ignition experiment, which demonstrated a strong flame resistance and self-extinguishing nature, rendering it superior to STF. This preparation strategy provides a promising sustainable and environmentally friendly method for fabrication of green tannin-furanic foam for industry applications.

Correction to: Synthesis and characterization of polyurethane rigid foam by using feedstocks received from renewable and recyclable resources

Correction to: Synthesis and characterization of polyurethane rigid foam by using feedstocks received from renewable and recyclable resources

Wood-based 3D printing: potential and limitation to 3D print building elements with cellulose & lignin

Under urgent sustainability targets, the building industry craves for renewable and recyclable biomaterials as cellulose is a fiber; Lignin is a plant-derived low-cost polymer with remarkable properties, yet its valorization is in its infancy. Recent studies have shown potentials to combine cellulose and lignin into a renewable bio-based material for the built environment, with the use of additive manufacturing to allow geometric customization and local control of material. However, previous studies also highlighted crucial issues to be solved. One main challenge is the lack of knowledge on combinations of lignin and cellulose with different binders to achieve a paste suitable for 3D printing, leading to a material applicable in the built environment. To contribute overcoming the challenge, this research aimed to explore various combinations of cellulose, lignin, and binders and to study the extrudability of the resulting paste using a clay extruder installed on a robotic arm. Several combinations were explored, evaluated, and compared. The four recipes with the highest scores were used to produce samples for tensile and three-point bending tests, water absorption and retention tests, and microscope analysis. The overall outcome has shown similarities between the mechanical properties of the mixture developed using methylcellulose as the binding agent and rigid polymer foams, such as the ones commonly used as insulation panels. Moreover, the material mix with the highest score in the preliminary assessment was further applied to fabricate samples with varied geometries to assess its potential and limitations combined with the fabrication process. Finally, two demonstrators were produced to explore the printing process for different geometric configurations: conceptual window frame and structural node were designed, and 3D printed as proof of concept.

Test on Shear Behavior of Double-Sided Thin Steel Plate Shear Wall Filled with Rigid Polyurethane Foam

A double-sided thin steel plate shear wall filled with rigid polyurethane foam (SWR) is proposed. A quasi-static monotonic loading test and quasi-static cycling loading test on shear behavior and the energy dissipation capacity of the SWR were carried out. Four kinds of test specimens, including the pure steel frames, the steel frame with double-sided thin steel plates, the SWR, and the SWR with an open hole, were tested. The results showed that compared with the pure steel frame, the erection of thin steel plates on both sides enhances the shear bearing capacity, initial shear stiffness, and energy consumption capacity. It turns out that the rigid foam polyurethane (RPUF) significantly increases the shear performance of the thin steel plate shear wall. The main reason for this is that the bond effect and support effect of the RPUF delay the out-of-plane buckling of thin steel plates and improve shear performance and energy dissipation capacity.

Study and Characterization of Regenerated Hard Foam Prepared by Polyol Hydrolysis of Waste Polyurethane.

In this paper, four different kinds of diols were used for the alcoholysis of waste thermoplastic polyurethane elastomers. The recycled polyether polyols were used to prepare regenerated thermosetting polyurethane rigid foam through one-step foaming. We used four different kinds of alcoholysis agents, according to different proportions of the complex, and we combined them with an alkali metal catalyst (KOH) to trigger the catalytic cleavage of the carbamate bonds in the waste polyurethane elastomers. The effects of the different types and different chain lengths of the alcoholysis agents on the degradation of the waste polyurethane elastomers and the preparation of regenerated polyurethane rigid foam were studied. Based on the viscosity, GPC, FT-IR, foaming time and compression strength, water absorption, TG, apparent density, and thermal conductivity of the recycled polyurethane foam, eight groups of optimal components were selected and discussed. The results showed that the viscosity of the recovered biodegradable materials was between 485 and 1200 mPa·s. The hard foam of the regenerated polyurethane was prepared using biodegradable materials instead of commercially available polyether polyols, and its compressive strength was between 0.131 and 0.176 MPa. The water absorption rate ranged from 0.7265 to 1.9923%. The apparent density of the foam was between 0.0303 and 0.0403 kg/m3. The thermal conductivity ranged from 0.0151 to 0.0202 W/(m·K). A large number of experimental results showed that the degradation of the waste polyurethane elastomers by the alcoholysis agents was successful. The thermoplastic polyurethane elastomers can not only be reconstructed, but they can also be degraded by alcoholysis to produce regenerated polyurethane rigid foam.

Fabrication of Rigid Isocyanate-Based Polyimide Foam Achieved Excellent Use Safety via Synergy between Expandable Graphite and Phosphorus-Containing Polyol

For the advantages of low cost, excellent thermal insulation, and sound absorption properties, the rigid isocyanate-based polyimide foam (RPIF) presents great application prospects as a building insulation material. However, its inflammability and the accompanying toxic fumes create huge safety hazard. In this paper, reactive phosphate-containing polyol (PPCP) is synthesized and employed with expandable graphite (EG) to obtain RPIF with excellent use safety. EG can be considered as an ideal partner for PPCP to weaken the drawbacks in toxic fume release. Limiting oxygen index (LOI), cone calorimeter test (CCT), and toxic gas results show that the combination of PPCP and EG can synergistically enhance flame retardancy and the use safety of RPIF owing to the unique structure of a dense char layer possessing a flame barrier and toxic gas adsorption effects. When EG and PPCP are simultaneously applied to the RPIF system, the higher EG dosage will bring higher positive synergistic effects in the use safety of RPIF. The most preferred ratio of EG and PPCP is 2:1 (RPIF-10-5) in this study; RPIF-10-5 shows the highest LOI, low CCT results and specific optical density of smoke, and low HCN concentration. This design and the findings are of great significance to improving the application of RPIF.

Directing the pore size of rigid polyurethane foam via controlled air entrainment

The interest in polyurethane rigid (PUR) foams as potent thermally insulating materials for a wide range of applications continues to grow as the minimization of CO2 emissions has become a global issue. Controlling the thermal insulation efficiency of PUR foams starts with the control of their morphology. Although the presence of micrometric air bubbles originating from air entrainment during the blending of the PU reactive mixture has been shown to influence the final PUR foam morphology, detailed experimental investigations on how exactly they affect the final PUR foam pore size are still lacking. To fill this gap, we use a double-syringe mixing device, which allows to control the number of air bubbles generated during a first air entrainment step, before using the same device to blend the reactive components in a sealed environment, avoiding further air entrainment. Keeping all experimental parameters constant except for the air bubble density in the reactive mixture, we can correlate changes of the final PUR foam morphology with the variation of the air bubble density in the initially liquid reactive mixture. Our results confirm recent findings which suggest the presence of two different regimes of bubble nucleation and growth depending on the presence or absence of dispersed air bubbles in the liquid reactive mixture. Our study pushes those insights further by demonstrating an inverse relation between the air bubble density in the liquid reactive mixture and the final pore volume of the PUR foam. For example, at constant chemical formulation and blending conditions, we could vary the final pore size between 400–1600 μm simply by controlling the amount of pre-dispersed air bubbles within the system. We are confident that the presented approach may not only provide a valuable model experiment to scan formulations in R&D laboratories, but it may also provide suggestions for the optimization of industrial processes.

Oligoetherols and polyurethane foams based on cyclotriphosphazene of reduced flammability

New oligoetherols with based on cyclotriphosphazene ring were synthesized by functionalization of hexachlorocyclotriphosphazene with glycidol followed by reaction with ethylene glycol and glycerol. Oligoetherols were characterized by IR, 1H-NMR, and MALDI-ToF and hydroxyl number as well as physical properties like density, viscosity and surface tension. The oligoetherols were further converted into polyurethane foams. The rigid foams of enhanced thermal stability and considerably diminished flammability were obtained and their apparent density, water uptake and polymerization shrinkage, thermal conductivity coefficient and thermal stability were determined. The flammability of foams was studied by microcalorimetric methods, horizontal flaming test and oxygen index. The obtained polyurethane foams with incorporated cyclotriphosphazene ring are self-extinguishing.Graphical abstract

Synthesis and characterization of polyurethane rigid foam by using feedstocks received from renewable and recyclable resources

The mimicry reactions used in the industrial field based on pure materials to obtain products is very important in order to achieve a circular economy and a green environment. This time around, the idea is that all raw materials are wastes. In addition to synthesizing biodiesel, this study aims to synthesize polyurethane rigid foams from recyclable materials such as liquid wastes and solid plastic wastes. The study follows preparation of a new class of biopolyols by reacting a mixture of crude glycerin-based polyol and epoxidized used cooking oil with polyethylene terephthalate, polyurethane, and bisphenol-polycarbonate wastes. Then, fabrication of polyurethane rigid foams by blending synthesized biopolyols with commercial polyol at ratios 20%, 40%, and 60% occurs. The properties of biopolyols and fabricated rigid foams was investigated by nuclear magnetic resonance, infrared spectrometer, thermal gravimetric analyzer, scanning electron microscope, and dynamic mechanical thermal analyzer. The results show that the biopolyols are valuable products for polyurethane manufactures. Moreover, the fabricated rigid foams show nonsignificant changes at the commercial and industrial level.

Chemical Recycling of Polyurethane Waste via a Microwave-Assisted Glycolysis Process.

In this work, we explored a microwave-assisted glycolysis process to chemically recycle rigid polyurethane (PU) foam waste to obtain a single-phase product with suitable physio-chemical properties as a secondary raw material for the preparation of new rigid PU products. Such an approach was compared to a conventionally heated (ConvH) process, analyzing the performances of different catalysts. The use of microwaves allowed a 94% decrease in the reaction time scale of rigid PU depolymerization, with a concurrent 45% reduction in energy expense. By using a PU/diethylene glycol mass ratio of 1.5, best performances were obtained with a 30 mmol/100gPU potassium acetate concentration, both in terms of the product viscosity and aromatic amine byproduct content. The glycolysis products recovered were employed in substitution to virgin polyol for rigid PU foam preparation, showing improved compressive strength and comparable thermal insulation properties up to a 30% content with respect to the traditional non-recycled counterpart.

Eco-friendly physical blowing agent mass loss of bio-based polyurethane rigid foam materials

Eco-friendly physical blowing agent mass loss of bio-based polyurethane rigid foam materials

Periodic hygrothermal properties of Salix liquefaction products / isocyanate rigid foam materials

Under specific circumstances, the liquefaction product of biomass polyol can be converted into hard polyurethane foam. In this study, the rigid foam material (RPUF) was created by reacting the liquefaction product of Salix psammophila with isocyanate. The mechanical properties, chemical structure, cell structure, and thermal stability of RPUF were characterized by mechanical properties tests, Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The impact strength, compressive strength, and flexural strength of RPUF after hygrothermal treatment showed a downward trend. FTIR showed that the change of temperature and humidity did not affect the chemical structure of RPUF. SEM showed that the destruction of cell structure of RPUF was increased with the extension of time. TGA showed that the initial decomposition temperature of RPUF was reduced by periodic hydrothermal treatment, and the residual carbon rate decreased with the extension of treatment time.

Fabrication of Rigid Polyimide Foams by Constructing Dual Crosslinking Network Structures

Herein, lightweight rigid polyimide foams (PIFs) with excellent mechanical and thermal properties were fabricated by constructing dual crosslinking structures combined with the thermal foaming of polyester ammonium salt (PEAS) precursor powders. The dual crosslinking network relied on the self-crosslinking of pararosaniline base (PA) and active crosslinking derived from the breakage of C═C bonds in 5-norbornene-2, 3-dicarboxylic anhydride (NA) under heating. The results showed that melt viscosity and micro-foaming behavior of PEASs and the cell morphology of PIFs could be regulated by varying the molar ratio of PA/NA and the number of repeating units amid crosslinking points. The compressive strength of PIFP1BMN3-5 (density: 165.5 kg·m–3) with dual crosslinking structures at 10% strain reached 1.36 MPa at room temperature and 0.75 MPa at 200 °C. The PIFs exhibited outstanding thermal properties with the initial thermal degradation temperature falling in a temperature range of 458.2–503.0 °C and the glass-transition temperatures exceeding 310 °C. In addition, PIFs exhibited excellent thermal insulation properties since the thermal conductivity of PIFs was between 0.048 and 0.065 W·m–1 K–1, and the temperature increase of the top surface of the cubic sample block (height: 15 mm) was approximately 20 °C when they were placed on a preheated hot stage at 200 °C for 30 min. Thus, mechanically strong rigid PIFs with dual crosslinking structures were successfully prepared, which show promising applications as lightweight, high-temperature-resistant structural materials in high-end engineering fields.