Comprehensive Analysis of the Influence of Expanded Vermiculite on the Foaming Process and Selected Properties of Composite Rigid Polyurethane Foams

This article presents the results of research on obtaining new polyurethane (PUR) foams modified with thermally expanded vermiculite. The filler was added in amount of 3 wt.% up to 15 wt.%. The additionally applied procedure of immersion the non-organic filler in H₂O₂ was performed to increase the exfoliation effect of thermally treated mineral and additional oxidation the surfaces. The effect of fillers on foaming process, cell structure, thermal insulation, apparent density, compressive strength, thermal properties, and flammability are assessed. The foaming process of PUR foams modified with vermiculite was comparable for all systems, regardless of the content of the filler. A slight increase in reactivity was observed, confirmed by a faster decrease in dielectric polarization for the system with modified vermiculite by H₂O₂. The modification of the reference system with the vermiculite increased the content of closed cells from 76% to 91% for the foams with the highest vermiculite content. Coefficient of thermal conductivity of reference foam and foams modified with vermiculite was in the range 24-26 mW/mK. The use of vermiculite up to 15 wt.% did not influence significantly on mechanical properties and flammability, which from an economic point of view is important because it is possible to reduce the cost of materials by introducing a cheap filler without deteriorating their properties.

Thermomechanical and Fire Properties of Polyethylene-Composite-Filled Ammonium Polyphosphate and Inorganic Fillers: An Evaluation of Their Modification Efficiency

The development of new polymer compositions characterized by a reduced environmental impact while lowering the price for applications in large-scale production requires the search for solutions based on the reduction in the polymer content in composites' structure, as well as the use of fillers from sustainable sources. The study aimed to comprehensively evaluate introducing low-cost inorganic fillers, such as copper slag (CS), basalt powder (BP), and expanded vermiculite (VM), into the flame-retarded ammonium polyphosphate polyethylene composition (PE/APP). The addition of fillers (5-20 wt%) increased the stiffness and hardness of PE/APP, both at room and at elevated temperatures, which may increase the applicability range of the flame retardant polyethylene. The deterioration of composites' tensile strength and impact strength induced by the presence of inorganic fillers compared to the unmodified polymer is described in detail. The addition of BP, CS, and VM with the simultaneous participation of APP with a total share of 40 wt% caused only a 3.1, 4.6, and 3 MPa decrease in the tensile strength compared to the reference value of 23 MPa found for PE. In turn, the cone calorimeter measurements allowed for the observation of a synergistic effect between APP and VM, reducing the peak heat rate release (pHRR) by 60% compared to unmodified PE. Incorporating fillers with a similar thermal stability but differing particle size distribution and shape led to additional information on their effectiveness in changing the properties of polyethylene. Critical examinations of changes in the mechanical and thermomechanical properties related to the structure analysis enabled the definition of the potential application perspectives analyzed in terms of burning behavior in a cone calorimetry test. Adding inorganic fillers derived from waste significantly reduces the flammability of composites with a matrix of thermoplastic polymers while increasing their sustainability and lowering their price without considerably reducing their mechanical properties, which allows for assigning developed materials as a replacement for flame-retarded polyethylene in large-scale non-loaded parts.

Synergistic effect of aluminum diethylphosphinate/sodium stearate modified vermiculite on flame retardant and smoke suppression properties of amino coatings

Various inorganic fillers are proved to be desirable synergists to improve the fire resistance of fire-retardant coatings. Herein, a functional filler (ANE) with flame retardant property was prepared by intercalating aluminum diethylphosphinate into microwave expanded vermiculite and grafting sodium stearate on its surface. The structure of ANE was fully characterized by FTIR, XRD, XPS and SEM analyses. Then ANE was applied to melamine modified urea-formaldehyde resin to produce fire-retardant coatings. The fire resistance test, TGA and cone calorimeter test demonstrate that ANE imparts great heat insulation, thermal stability, and flame retardancy to the coatings. Moreover, the introduction of ANE exhibits an excellent synergistic effect on reducing the heat release and smoke emission of the coatings. Specifically, with the addition of 3 wt% ANE, the heat release rate and smoke density grade of the coatings are decreased by 25.24% and 60.32%, respectively, compared to that without ANE. The excellent flame retardancy and smoke suppression performances of the coatings are mainly attributed to the formation of more cross-linking structures in the carbon layers, resulting in a more stable and compact char structure. In addition, the good hydrophobicity of ANE coatings can ensure the durability of flame retardancy.

Vermiculite Filler Modified with Casein, Chitosan, and Potato Protein as a Flame Retardant for Polyurethane Foams

In this study, polyurethane (PU) composite foams were modified with 2 wt.% of vermiculite fillers, which were themselves modified with casein, chitosan, and potato protein. The impact of the fillers on selected properties of the obtained composites, including their rheological (foaming behavior, dynamic viscosity), thermal (temperature of thermal decomposition stages), flame-retardant (e.g., limiting oxygen index, ignition time, heat peak release), and mechanical properties (toughness, compressive strength (parallel and perpendicular), flexural strength) were investigated. Among all the modified polyurethane composites, the greatest improvement was noticed in the PU foams filled with vermiculite modified with casein and chitosan. For example, after the addition of modified vermiculite fillers, the foams' compressive strength was enhanced by ~6-18%, their flexural strength by ~2-10%, and their toughness by ~1-5%. Most importantly, the polyurethane composites filled with vermiculite filler and modified vermiculite fillers exhibited improved flame resistance characteristics (the value of total smoke release was reduced by ~34%, the value of peak heat release was reduced by ~25%).

Experimental Investigation of the Mechanical Properties and Fire Behavior of Epoxy Composites Reinforced by Fabrics and Powder Fillers

Different types of fabrics, such as aramid (A), carbon (C), basalt (B), glass (G), and flax (F), as well as powder fillers, were used to manufacture the epoxy-based hybrid composites by the hand-lay-up method. In this work, a few research methods, including hardness, flexural tests, puncture impact behavior, as well as cone calorimetry (CC) measurements, were applied to determine the impact of type fillers and order of fabrics on the performance and burning behavior of hybrid composites. The mechanical properties were evaluated to correlate with the microstructure and consider together with thermogravimetric analysis (TGA) data.

Characterization of Ethylene-propylene Composites Filled with Perlite and Vermiculite Minerals: Mechanical, Barrier, and Flammability Properties

Perlite and vermiculite are naturally occurring minerals, commonly used by industry to obtain highly thermoisolative and/or non-flammable materials. However, there has been little research into the preparation and application of rubber compounds containing these inexpensive mineral fillers. Here, we show the benefits of perlite and vermiculite minerals as fillers for ethylene-propylene rubber (EPM) composites. To obtain more uniform dispersion and improved compatibility between the minerals and the elastomer matrix, 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (AMIMTFSI) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) imidazolium ionic liquids (ILs) were added. The mineral fillers were found to be attractive semi-reinforcing fillers, which also act as flame retardants in the elastomer composites. Furthermore, a higher content of vermiculite mineral significantly reduced the air permeability of the composites. The incorporation of ionic liquids into the EPM-filled systems had a considerable effect on the torque increment, crosslink density, and more importantly the flammability of the studied compounds. The application of 2.5 parts per hundred parts of rubber (phr) BMIMTFSI, in particular, reduced the flammability of the EPM composite, as the maximum heat release rate (HRR_max) decreased from 189.7 kW/m² to 170.2 kW/m².

Thermal insulation with 2D materials: liquid phase exfoliated vermiculite functional nanosheets

Phyllosilicates are layered materials possessing unique thermal properties, commonly exploited in their multilayered crystalline form as refractory insulators and heating elements. A more versatile use of such materials, however, would require their existence in the form of inks and dispersions ready to be patterned. Within this framework, the liquid-phase exfoliation of low-cost, low-purity materials such as bulk multiphasic minerals and powders represents an economically advantageous approach for the production of 2D nano-sized objects with a defined composition, size and morphology. Here, ultrasound-assisted exfoliation and shear-mixing of a multi-phasic vermiculite in mild acidic aqueous solutions were employed to successfully obtain dispersions of mono- and few-layer thick clay nanosheets. The exfoliated materials were thoroughly investigated through granulometry, X-Ray Diffraction (XRD), specific surface area measurements and AFM imaging. Despite the fact that the lateral size and the thickness distribution of exfoliated flakes obtained with the two approaches appear similar, the ultrasound-assisted exfoliation process yielded a larger amount of mono- and bi-layer thick flakes as well as materials with a higher specific surface area. XRD analysis revealed that the use of ultrasound waves in an acidic environment results in the complete exfoliation of the vermiculite layer, whereas the use of shear forces under the same conditions results in the exfoliation of hydrobiotite and mica crystalline phases. Thermal conductivity measurements provided clear evidence on how the structural changes - arising from the exfoliation process - have a direct impact on the properties of the exfoliated clay. Remarkably, compared to the raw material, the thermal conductivity of the exfoliated material decreases by 25%, reaching the ultra-low thermal conductivity regime (<0.1 W m^-1 K^-1). Our approach may enable in the future the generation of patterns of thermal insulators onto different surfaces by applying vermiculite nanosheets in the form of dispersions and printable inks.