Cellular Plastics Research Articles

Effects of Testing Methods and Sample Configuration on the Flexural Properties of Extruded Polystyrene.

Extruded polystyrene (XPS) is frequently used in the construction of many different structures. Therefore, it is necessary to appropriately characterize its mechanical properties to ensure the safety of said structures. Among the available characterization tests, static bending tests are simple and easy to perform; owing to these characteristics, they should be performed more frequently than other tests. In static bending tests on XPS, there are several challenges owing to the high flexibility of XPS, and the chosen testing method and sample configuration affect the accuracy of characterization. For cellular plastics, including XPS, three-point bending (TPB) test methods are standardized by the International Organization for Standardization (ISO) and Japanese Industrial Standards (JIS) as in ISO 1209-2:2007 and JIS K 7221-2:2006, respectively, where the sample configurations are determined. Therefore, TPB tests of cellular plastics have been conventionally performed based on these standardized methods to characterize the bending properties. In contrast, investigations on the effects of testing methods and sample configurations have often been neglected due to the existence of these standardized methods. However, to characterize the bending properties of XPS accurately, the effects of the testing method and sample configuration must be examined in detail. In this study, three bending properties (Young's modulus, proportional limit stress, and bending strength) of samples cut from an XPS panel were determined using three-point bending (TPB), four-point bending (FPB), and compression bending (CB) tests with varying sample span/depth ratios from 5 to 50 at intervals of 5, and statistical analyses were performed to determine the relevance of the tests. The effect of sample configuration on Young's modulus could be reduced when the span/depth ratio range was 25-50, 25-50, and 15-50 in the TPB, FPB, and CB tests, respectively, whereas that on the proportional limit stress was reduced in the span/depth ratio range of 5-50, 20-50, and 15-50 in the TPB, FPB, and CB tests, respectively. Additionally, the effect on the bending strength was reduced when the span/depth ratio range was 5-50, 20-50, and 5-50 in the TPB, FPB, and CB tests, respectively. Therefore, these results suggest that the TPB and CB tests were more feasible than the FPB test when the span/depth ratio was determined as being 25-50 and 15-50, respectively. However, clear differences were observed in the sample bending properties determined in these tests. In light of these findings, further studies should be conducted to elucidate these differences.

Experimental and phenomenological investigations on the strain rate sensitivity of rigid PVC foams at strain rates of 0.005 s−1 to 600 s−1

Polymeric foams are often subjected to high strain rates in various industrial applications, especially the transportation sector, and experience significant deformations. An in-depth comprehension of the dynamic mechanical characteristics of polymeric foam is essential for devising effective engineering design approaches. Previous studies have extensively utilized Split Hopkinson Pressure Bar (SHPB) apparatuses to test polymeric foams dynamically; however, these studies faced technical limitations in specimen size, preventing compliance with the ASTM D1621 standard test method for rigid cellular plastics. A customized pneumatic apparatus equipped with a massive impacting bullet and sacrificial excess energy absorbing system was employed to complete the mechanical material characterization of Polyvinyl Chloride (PVC) foams, following the ASTM D1621 standard, to address previous technical limitations. PVC foams with six different nominal densities were subjected to strain rates ranging from 0.005 s−1 to 600 s−1. Loading was conducted parallel and perpendicular to the foam rise direction to investigate dynamic anisotropic material characteristics. A comparison of tests conducted at strain rates of 0.005 s−1 and 400 s−1 revealed an average increase of 35.1 % in the plateau stress. The phenomenological Nagy model was combined with a nonlinear Avalle relationship and revised with a new term, supported by findings from the present study, to characterize the complete stress/strain response, for the range of strain rates considered in this research. The calibrated model exhibited an average error of 1.7 % in the predicted plateau stress. The results indicated that testing under a single dynamic strain rate was sufficient to characterize the rate sensitivity of the PVC foam in the dynamic regime. Furthermore, the influence of relative density on the foam rate sensitivity was quantified, revealing a plateau in the strength enhancing effect of density at a nominal relative density of 0.125.

Sample geometry transformation for mechanical tests of constructional materials in an FDM structure

The aim was to obtain a rough determination of the dimensions and shape of a sample for an experimental study of the mechanical characteristics of filamentary FDM-printing structures with a low filling at central tension. The sample geometry was designed based on the dimensions and shape provided in the GOST 17370-2017 “Cellular rigid plastics. Tension testing method”. The research methods included the finite element analysis of stress state parameters in an automated environment, elements of the stiffened shell theory and experimental testing of samples. The theory of stiffened shells was used to simplify the geometry of the finite element model for the studied samples. Finite element analysis was carried out in a linear formulation and, based on the results of its combination with the analysis of the technological model of a designed sample, a decision on transforming the sample geometry was made. The samples were produced using a “line” template with an orientation along the longitudinal axis of the sample. According to the results of testing the samples, a conclusion about the success of implied transformation was made. The success criterion involves the destruction of an FDM sample within the limits of the working part. As a result, both external and internal geometries of the prototype sample were transformed. This allowed the main emphasis in the work of the stretchable FDM sample to be shifted to its working part and the trajectory of power flows to be adjusted according to the FDM-printing specifics. Experimental testing of FDM samples with a low “line” template filling showed a consistently satisfactory result: fractures occurred in the working part of test samples. In the course of the studies, the general trend in the dependence of the force flow distribution over the sample volume on the combination of the printing thread trajectory with external and internal geometries of the sample was determined. Future work will focus on a more detailed analysis and formalisation of the obtained results with regard to various printing templates.

Thermal Performance Study of a Cement-Based Mortar Incorporating EPS Beads

Recycling plastic waste has been one of the most significant challenges in the recent decade. The reuse of one of the most produced cellular plastics (i.e. EPS) within a conventional construction binder can contribute, simultaneously, to waste elimination and improving energy performances of the building envelopes. This work investigates the recycling of expanded polystyrene (EPS) waste within a cement-based matrix. The aim is to develop a lightweight, energy-efficient composite for eco-construction. Portland cement was mixed with a small amount of gypsum (4 wt%) before adding EPS aggregates ranging from 0–0.6 wt%. The thermal properties were determined using two different non-destructive methods, the transient plane source technique (Hot Disk Method) and the Flash method. The experimental results showed a remarkable decrease of 54, 12, and 36% in thermal conductivity, thermal diffusivity, and density, respectively. These results indicate the improvement of thermal resistance of EPS-cement-gypsum- mixes. In addition, water absorption and compressive tests revealed that cement-based composites containing EPS beads have improved durability and can be used for structural and insulation purposes. Finally, Numerical results indicated that energy savings of up to 18% may be achieved by applying produced waste-based mortar, underscoring the promise of using this product for building energy efficiency benefits.

Modeling the Nonlinear Deformation of Highly Porous Cellular Plastics Filled with Clay Nanoplatelets.

Rigid low-density plastic foams subjected to mechanical loads typically exhibit a nonlinear deformation stage preceding failure. At moderate strains, when the geometrical nonlinearity is negligible, such foam response is predominantly caused by the nonlinearity of deformation of their principal structural elements—foam struts. Orientational averaging of stresses in foam struts enables estimation of the stresses taken up by foams at a given applied strain. Based on a structural model of highly porous anisotropic cellular plastics filled with clay nanoplatelets and the orientational averaging, a method for calculating their nonlinear deformation is derived in terms of structural parameters of the porous material, the mechanical properties of the monolithic polymer, and filler particles and their spatial orientation. The method is applied to predicting the tensile stress-strain diagrams of organoclay-filled low-density rigid polyurethane foams, and reasonable agreement with experimental data is demonstrated.

Systematic Experimental Evaluation of Function Based Cellular Lattice Structure Manufactured by 3D Printing

Additive manufacturing (AM) has a greater potential to construct lighter parts, having complex geometries with no additional cost, by embedding cellular lattice structures within an object. The geometry of lattice structure can be engineered to achieve improved strength and extra level of performance with the advantage of consuming less material and energy. This paper provides a systematic experimental evaluation of a series of cellular lattice structures, embedded within a cylindrical specimen and constructed according to terms and requirements of ASTMD1621-16, which is standard for the compressive properties of rigid cellular plastics. The modeling of test specimens is based on function representation (FRep) and constructed by fused deposition modeling (FDM) technology. Two different test series, each having eleven test specimens of different parameters, are printed along with their replicates of 70% and 100% infill density. Test specimens are subjected to uniaxial compressive load to produce 13% deformation to the height of the specimen. Comparison of results reveals that specimens, having cellular lattice structure and printed with 70% infill density, exhibit greater strength and improvement in strength to mass ratio, as compared to the solid printed specimen without structure.

Bioinspired Multifunctional Cellular Plastics with a Negative Poisson's Ratio for High Energy Dissipation.

Cellular plastics have been widely used in transportation, aerospace, and personal safety applications owing to their excellent mechanical, thermal, and acoustic properties. It is highly desirable to impart them with a complex porous structure and composition distribution to obtain specific functionality for various engineering applications, which is challenging with conventional foaming technologies. Herein, it is demonstrated that this can be achieved through the controlled freezing process of a monomer/water emulsion, followed by cryopolymerization and room temperature thawing. As ice is used as a template, this method is environmentally friendly and capable of producing cellular plastics with various microstructures by harnessing the numerous morphologies of ice crystals. In particular, a cellular plastic with a radially aligned structure shows a negative Poisson's ratio under compression. The rigid plastic shows a much higher energy dissipation capability compared to other materials with similar negative Poisson's ratios. Additionally, the simplicity and scalability of this approach provides new possibilities for fabricating high-performance cellular plastics with well-defined porous structures and composition distributions.

Recent advancements in manufacturing technologies of microcellular polymers: a review

Significant research efforts are being pursued by numerous plastic foaming industries towards the transformation of macrocellular polymer foam to microcellular and imminent future is trending towards nanocellular polymer foams. These novel foamed plastic possess enhanced properties and easy tunability which could potentially fulfill many of the ever-evolving industrial requirements. These industrial requirements have led to several advancements in the current manufacturing technologies and as a result, new industrial-scale production technologies are being researched upon cellular plastics and its allied composites. The microcellular polymeric foams have huge industrial demand due to their improved properties such as specific strength, energy absorption, and thermal/electrical/acoustic insulation compared to their unfoamed counterparts. This review article aims to summarise the existing manufacturing technologies for producing microcellular polymers and provide an up-to-date report on the recent advancements in these manufacturing technologies.

Experimental Study on the Self-extinguishing Performance of Extruded Polystyrene Insulation for Buildings and Suggestions on Institutional Management

The Korea Industrial Standards (KS) stipulates methods and test procedures for measuring the horizontal combustibility of cellular plastics exposed to small flames (KS M ISO 9772:2018) and recommendations regarding the magnetic digestion of extruded polystyrene insulation (XPS) for measurement results (KS M 3808:2020). Although products that are certified to conform to KS standards must have burning characteristics (self-extinguishing), they are incinerated and spread by welds at construction sites, causing significant human and property damages. In this study, XPS produced by five companies, certified by KS, and sold in the market were purchased and tested for ignition and diffusion caused by a weld bullion at a construction site. The results showed that the five products had differences in performance. Three out of the five products were found to be self-saturated, but the other two were easily ignited and diffused, making it difficult for them to be self-extinguishing. Based on the result of this experimental investigation in line with the KS regulations, all the three types of products, including two types of products that were incinerated through weld defects, were found to be non-self- extinguishing, as specified in KS M 3808.

Polystyrene microplastics decrease accumulation of essential fatty acids in common freshwater algae

Despite growing concern about the occurrence of microplastics in aquatic ecosystems there is only rudimentary understanding of the pathways through which any adverse effects might occur. Here, we assess the effects of polystyrene microplastics (PS-MPs; <70 μm) on a common and widespread algal species, Chlorella sorokiniana. We used laboratory exposure to test the hypothesis that the lipids and fatty acids (FAs) are important molecules in the response reactions of algae to this pollutant. Cultivation with PS-MPs systematically reduced the concentration of essential linoleic acid (ALA, C18:3n-3) in C. sorokiniana, concomitantly increasing oleic acid (C18:1n-9). Among the storage triacylglycerols, palmitoleic and oleic acids increased at the expenses of two essential fatty acids, linoleic (LIN, C18:2n-6) and ALA, while PS-MPs had even more pronounced effects on the fatty acid and hydrocarbon composition of waxes and steryl esters. The FA composition of two major chloroplast galactolipids, monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), were affected implying changes in the conformational structure of photosynthetic complexes in ways that can impair the photosynthesis. These data reveal how exposure to polystyrene microplastics can modify the concentrations of lipid molecules that are important intrinsically in cell membranes, and hence the lipid bilayers that could form an important barrier between algal cellular compartments and plastics in the aquatic environment. Changes in lipid synthesis and fatty acid composition in algae could also have repercussions for food quality, growth and stressor resistance in primary consumers. We advocate further studies of microplastics effects on the lipid composition of primary producers, and of their potential propagation through aquatic food webs.

Экспериментальные исследования показателей воздухопроницаемости композита «Поропласт CF»

Approximately half of the total energy consumed in the world is used for heating buildings and structures. Therefore, it is quite logical that an important component of almost all national long-term development pro-grams focused on the world economy of fuel and energy resources is to ensure the most effective thermal insulation of heating systems and enclosing structures of the new buildings. The use of carbamide cellular plastics as heat insulation of buildings enclosing structures and the requirements of regulatory documents on the parameters of acceptable air permeability determine the need for an experimental determination of their resistance to air penetration. The purpose of experimental studies of air permeability indicators forcar-bamide cellular plastics is to establish numerical values and to identify patterns of their changes depending on the density of the studied material, which to varying degrees will affect the total indicator of normalised resistance to air penetration of multilayer enclosing structures. An experimental and analytical evaluation of the studied indicators of air permeability of different density of carbamide cellular plastics was performed. This consists in an innovative heat-insulating product constructed directly on the objects under construction using high-performance generating plants and monolithically stacked to ensure thermal protection of enclos-ing structures. The study presents the experimental data on the air permeability of carbamide cellular plas-tics of various densities, which is connected with their use as thermal protection of enclosing structures of the building envelope. The newly obtained data on the air permeability of carbamide cellular plastics with different density values, provided by TU-2254-002-16602333-02, make it possible to evaluate the satisfacto-riness of multilayer enclosing structures to normalised indicators of resistance to air penetration in accord-ance with the regulatory document "SP 50.13330.2012 – Thermal protection of buildings. Updated version of SNiP 23-02-2003".

Methodology for estimating pyrolysis rates of charring insulation materials using experimental temperature measurements

This paper presents the application of a simplified method to estimate pyrolysis rates from rigid closed-cell cellular plastics by means of experimental temperature measurements. These materials are extremely effective in meeting energy efficiency goals in buildings and their safe use should also be enabled and optimised by undertaking comprehensive fire safety analyses. The proposed methodology consists of determining the mass loss as a function of the thermal evolution by applying a mass conversion directly using thermogravimetric data under non-oxidative conditions. In order to verify this simplified method, an experimental programme based on 100mm thick samples of rigid polyisocyanurate foam was conducted using a Cone Calorimeter, obtaining measurements of mass loss and temperature within the core of the material. A Monel plate was used on top of the sample in order to represent a simpler boundary condition by eliminating the smouldering process of the charred material. Although the pyrolysis rates using this methodology did not provide a perfect fit with experimental data, they showed similar trends, with a slightly delayed prediction but still accurate magnitude. This methodology presents potential for fire safety engineering applications in two domains: (1) as a complementary technique to improve the interpretation of results from standard and ad-hoc testing, and (2) as a design technique for the evaluation of potential heat release contribution and gaseous emissions of assemblies incorporating insulation materials.

Manifestation of the shape-memory effect in polyetherurethane cellular plastics, fabric composites, and sandwich structures under microgravity

The results of experiments that were performed to test the feasibility of creating sandwich structures (consisting of thin-layer sheaths of polymer composites and a cellular polymer core) with the shapememory effect as models of the transformable components of space structures have been given. The data obtained indicate that samples of sandwich structures under microgravity conditions on board the International Space Station have recovered their shape to almost the same degree as under terrestrial conditions, which makes it possible to recommend them for creating components of transformable space structures on their basis.

Experimental investigations and numerical simulations of notch effect in cellular plastic materials

Cellular plastics are light weight structures with many applications in civil, aeronautical, automotive and mechanical engineering. Properties of cellular materials depend on the properties of the solid material, on the shape and dimensions of the cellular structure and on the relative density of the cellular material. Most of cellular plastic materials are crushing in compression and have a brittle behavior in tension. The effect of notches represents an important issue in such materials, taking into account that for packing applications for example, notches/holes should be introduced in the cellular material. This paper investigates the effect of notches in compression for three different densities 100, 145 and 300 kg/m3 polyurethane (PUR) foams. Experimental investigations were performed on rectangular blocks of 100×100×25 mm with 16, 28 and 40 mm central holes. The mechanism of damage was monitored with an IR camera FLIR A40M. Purpose of the numerical simulations was to calibrate a material model, based on compression test for un-notched specimens using the CRUSHABLE FOAM models implemented in ABAQUS SIMULIA. Then the material models were used to simulate the experimental tests on notched blocks. Good agreement was obtained for the load - displacement curves obtained experimentally and from simulation. Also the plastic deformation patterns observed experimentally by IR thermograpghy were obtained numerically using the CRUSHABLE FOAM material model.

Current Issues and Challenges in Polypropylene Foaming: A Review

Thermoplastic foams have several advantages in comparison with unfoamed polymers such as lightweight, high strength to weight ratio, excellent insulation property, high thermal stability, high impact strength and toughness, as well as high fatigue life. These outstanding properties lead cellular plastics to various industrial applications in packaging, automotive parts, absorbents, and sporting equipment. Nowadays, polypropylene (PP), because of its outstanding characteristics such as low material cost, high service temperature, high melting point, high tensile modulus, low density, and excellent chemical resistance, is a major resin in the foaming industry. However, foaming of conventional PP is limited by its low melt strength leading to poor cell morphology, cell rupture/coalescence and limited density reduction. To improve PP melt strength, several strategies including particle addition as nucleating agent, introduction of long chain branching, blending with high melt strength polymers and crosslinking have been proposed. In this review, these issues are discussed and analyzed in terms of mechanical, thermal, and rheological characterizations.

Estimation of the elastic constants of highly porous cellular plastics reinforced with fibres embedded in foam struts

In order to enhance the mechanical properties of polymer foams, fillers of different materials and sizes are being applied. Fibrous fillers shorter than the characteristic foam cell dimensions have the potential of efficient reinforcement, due to their high aspect ratio, without detrimentally interfering with foam structure. A theoretical model is developed for evaluation of the effect of filler on foam stiffness. The elastic response of rigid polymer foams filled with short fibres, of length commensurable with that of foam struts, is modelled by using the orientational averaging technique. Explicit expressions for components of the stiffness tensor of composite foams are derived in terms of elasticity characteristics of the polymer and reinforcing fibres, fibre content, foam density, and parameters of the orientational distribution of foam struts. The model is applied to describing the foam stiffness as a function of fibre loading of polyurethane foams filled with milled carbon fibres.

Function of silicon oil in the castor oil based rigid polyurethane foams

Abstract Rigid polyurethane foams are one of the most important cellular plastics. Castor oil was modified with glycerol to form the polyol and reacted with methyl diisocyanate and different proportions of silicon oil to achieve rigid polyurethane foam. Prepared foam was tested for its density and mechanical properties. It was found that compressive and flexural strength was improved with silicon oil content. The morphology of the resulted foams was also studied using scanning electron microscope, and it was observed that the cell size was reduced with silicon oil content, indicating a more dense and packed structure. With further increase in the silicon oil content, foam properties showed a slight decrease in value.

Calculating the elastic constants of a highly porous cellular plastic with an oriented structure

A method for calculating the elastic constants of high-porosity cellular materials is proposed on the assumption that their oriented structure can be considered as a linear transform of some random structure. A simplified procedure to take into account the effect of gas pressure in closed-cell anisotropic solids on their elastic constants is also suggested. Calculations performed on the basis of a strut model elaborated earlier for highly porous materials are compared with experimental results for light cellular polyurethane plastics.

A refined strut model for calculating the elastic constants of highly porous cellular plastics by the method of orientational averaging

A model is presented for calculating the linear elastic constants of high-porosity cellular plastics by orientationally averaging the rigidity tensor of a structural element consisting of an air sheath and a loadcarrying element in the form of a straight strut with a piecewise constant cross section. The load-carrying element can resist the axial and shear loads and bending moments applied to its ends. The nonuniform orientational distribution of the elements is also taken into account. The calculation results obtained are compared with some literature data.

Impregnation of Large Glass-fibre-reinforced Cellular Plastics

An examination is made of features of technology for producing large glass-fibre-reinforced cellular plastics that ensures, at a given thickness of the cellular pack, the optimum content of binder and the required combination of physicomechanical properties of the glass-fibre-reinforced cellular plastics formed.