scholarly journals Reinforcement Efficiency of Cellulose Microfibers for the Tensile Stiffness and Strength of Rigid Low-Density Polyurethane Foams

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2725 ◽  
Author(s):  
Jānis Andersons ◽  
Mikelis Kirpluks ◽  
Ugis Cabulis
Keyword(s):  
Mechanical Properties ◽  
Polyurethane Foams ◽  
Low Density ◽  
Mechanical Reinforcement ◽  
Tensile Stiffness ◽  
Structural Applications ◽  
Cellulose Microfibers ◽  
Renewable Material ◽  
Reinforcement Efficiency ◽  
Pu Foams

Rigid low-density closed-cell polyurethane (PU) foams are widely used in both thermal insulation and structural applications. The sustainability of PU foam production can be increased by using bio-based components and fillers that ensure both enhanced mechanical properties and higher renewable material content. Such bio-based foams were produced using polyols derived from rapeseed oil and microcrystalline cellulose (MCC) fibers as filler. The effect of MCC fiber loading of up to 10 wt % on the morphology, tensile stiffness, and strength of foams has been evaluated. For estimation of the mechanical reinforcement efficiency of foams, a model allowing for the partial alignment of filler fibers in foam struts was developed and validated against test results. It is shown that although applying MCC fibers leads to modest gains in the mechanical properties of PU foams compared with cellulose nanocrystal reinforcement, it may provide a higher content of renewable material in the foams.

Mechanical properties of low-density paper

2020 ◽  
Vol 35 (1) ◽  
pp. 61-70
Author(s):  
Na Young Park ◽  
Young Chan Ko ◽  
Lili Melani ◽  
Hyoung Jin Kim
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Structural Change ◽  
Tensile Testing ◽  
Tensile Modulus ◽  
Gauge Length ◽  
Efficiency Factor ◽  
Low Density ◽  
Tensile Stiffness ◽  
Lower Tensile Strength

AbstractFor the mechanical properties of paper, tensile testing has been widely used. Among the tensile properties, the tensile stiffness has been used to determine the softness of low-density paper. The lower tensile stiffness, the greater softness of paper. Because the elastic region may not be clearly defined in a load-elongation curve, it is suggested to use the tensile modulus which is defined as the slope between the two points in the curve. The two points which provide the best correlation with subjective softness evaluation should be selected. Low-density paper has a much lower tensile strength, but much larger elongation at the break. It undergoes a continuous structural change during mechanical testing. The degree of the structural change should depend on tensile conditions such as the sample size, the gauge length, and the rate of elongation. For low-density paper, the tensile modulus and the tensile strength should be independent of each other. The structure efficiency factor (SEF) is defined as a ratio of the tensile strength to the tensile modulus and it may be used a guideline in developing superior low-density paper products.

Cryogenic thermal insulating and mechanical properties of rigid polyurethane foams blown with hydrofluoroolefin: Effect of perfluoroalkane

2021 ◽  
pp. 0021955X2110626
Author(s):  
Tae Seok Kim ◽  
Yeongbeom Lee ◽  
Chul Hyun Hwang ◽  
Kwang Ho Song ◽  
Woo Nyon Kim
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Thermal Stability ◽  
Cell Size ◽  
Thermal Insulation ◽  
Coefficient Of Thermal Expansion ◽  
Lower Surface ◽  
Polyurethane Foams ◽  
Insulation Material ◽  
Pu Foams

The effect of perfluoroalkane (PFA) on the morphology, thermal conductivity, mechanical properties and thermal stability of rigid polyurethane (PU) foams was investigated under ambient and cryogenic conditions. The PU foams were blown with hydrofluorolefin. Morphological results showed that the minimum cell size (153 μm) was observed when the PFA content was 1.0 part per hundred polyols by weight (php). This was due to the lower surface tension of the mixed polyol solution when the PFA content was 1.0 php. The thermal conductivity of PU foams measured under ambient (0.0215 W/mK) and cryogenic (0.0179 W/mK at −100°C) conditions reached a minimum when the PFA content was 1.0 php. The low value of thermal conductivity was a result of the small cell size of the foams. The above results suggest that PFA acted as a nucleating agent to enhanced the thermal insulation properties of PU foams. The compressive and shear strengths of the PU foams did not appreciably change with PFA content at either −170°C or 20°C. However, it shows that the mechanical strengths at −170°C and 20°C for the PU foams meet the specification. Coefficient of thermal expansion, and thermal shock tests of the PU foams showed enough thermal stability for the LNG carrier’s operation temperature. Therefore, it is suggested that the PU foams blown by HFO with the PFA addition can be used as a thermal insulation material for a conventional LNG carrier.

Additive manufacturing of ceramics: Present status and future perspectives

2021 ◽  
Author(s):  
Mainak Saha ◽  
Manab Mallik
Keyword(s):  
Mechanical Properties ◽  
Additive Manufacturing ◽  
Microstructure Evolution ◽  
Review Article ◽  
Low Density ◽  
Structure Property ◽  
Future Perspectives ◽  
Structural Applications ◽  
Systematic Structure ◽  
State Of Research

At present, fabrication of ceramics using AM-based techniques mainly suffers from two primary limitations, viz: (i) low density and (ii) poor mechanical properties of the finished components. It is worth mentioning that the present state of research in the avenue of AM-based ceramics is focussed mainly on fabricating ceramic and cermet components with enhanced densities and improved mechanical properties. However, to the best of the authors’ knowledge, not much is known about the microstructure evolution and its correlation with the mechanical properties of the finished parts. Addressing the aforementioned avenue is highly essential for understanding the utilisation of these components for structural applications. To this end, the present review article is aimed to address the future perspectives in this avenue has been provided with a special emphasis on the need to establish a systematic structure-property correlation in these materials.

Investigation on Improvement of Flexural Behavior of Low-Density Cellular Concrete through Fiber Reinforcement for Non-Structural Applications

2019 ◽  
Vol 2673 (10) ◽  
pp. 641-651
Author(s):  
Arman Abdigaliyev ◽  
Jiong Hu
Keyword(s):  
Mechanical Properties ◽  
Lightweight Concrete ◽  
Construction Material ◽  
Flexural Behavior ◽  
Unit Weight ◽  
Slight Reduction ◽  
Low Density ◽  
Hybrid Fibers ◽  
Structural Applications ◽  
Cellular Concrete

During the last decades, cellular lightweight concrete (CLC), or foamed concrete, has been experiencing greater interest in geotechnical, structural, and non-structural applications. The low density and high flowability makes it a favorable construction material in relation to handling, placing, and construction costs. However, the applications of low-density cellular concrete (LDCC), the category of CLC with a unit weight less than 50 pounds per cubic foot (801 kg/m3) and generally without fine aggregates, are limited mostly to backfill applications in geotechnical engineering. The main reason lies in the brittleness of the material and low to zero resistance to flexural loads. Fiber-reinforced LDCC may be a reasonable solution to improve mechanical properties and expand the application range of the material. This study investigated the effects of adding polypropylene and hybrid fibers on physical and mechanical properties of LDCC and the feasibility of expanding LDCC utilization to non-structural applications. Results showed that although there is a slight reduction of flowability and compressive strength, the flexural behavior of LDCC can be significantly improved with the incorporation of fibers. The flexural strength and flexural toughness of LDCC was found to increase from 26.8 pounds per square inch (psi) (0.18 MPa) to 217.5 psi (1.48 MPa), and from 5.67 lb-in. (0.64 kN-mm) to 292 lb-in. (33.0 kN-mm) respectively at a 1.0% addition rate of a fibrillated polypropylene fiber selected in this study, which makes it a feasible material for non-structural applications.

Microstructural and Mechanical Properties Changes of Silicon Nitride Based Ceramic Using Post-Sintering Heat Treatment

2012 ◽  
Vol 727-728 ◽  
pp. 1085-1091
Author(s):  
José Vitor C. Souza ◽  
O.M.M. Silva ◽  
E.A. Raymundo ◽  
João Paulo Barros Machado
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Fracture Toughness ◽  
Grain Size ◽  
Wear Resistance ◽  
High Hardness ◽  
Gas Pressure ◽  
Low Density ◽  
Nitrogen Gas ◽  
Structural Applications

Si3N4based ceramics are widely researched because of their low density, high hardness, toughness and wear resistance. Post-sintering heat treatments can enhance their properties. Thus, the objective of the present paper was the development of a Si3N4based ceramic, suitable for structural applications, by sintering in nitrogen gas pressure, using AlN, Al2O3, and Y2O3as additives and post-sintering heat treatment. The green bodies were fabricated by uniaxial pressing at 80 MPa with subsequent isostatic pressing at 300 MPa. The samples were sintered at 1900°C for 1 h under N2gas pressure of 0.1 MPa. Post-sintering heat treatment was performed at 1500°C for 48 h under N2gas pressure of 1.0 MPa. From the results, it was observed that after post-sintering heat treatment there was a reduction of α-SiAlON phase and increase of β-Si3N4phase, with consequent changing in grain size, decrease of fracture toughness and increase of the Vickers hardness.

New polyols with isocyanuric structure by thiol-ene “click” chemistry reactions

2016 ◽  
Vol 53 (6) ◽  
pp. 639-662 ◽  
Author(s):  
Ram K Gupta ◽  
M Ionescu ◽  
X Wan ◽  
D Radojcic ◽  
N Bilic
Keyword(s):  
Mechanical Properties ◽  
Click Chemistry ◽  
Flame Retardancy ◽  
Reaction Rates ◽  
Polyurethane Foams ◽  
Storage Tanks ◽  
Rigid Polyurethane Foams ◽  
High Yields ◽  
Pu Foams ◽  
Very High

New polyols with isocyanuric structure were synthesized by thiol-ene “click” chemistry of triallyl isocyanurate with 1-thioglycerol and 2-mercaptoethanol. The synthesized polyols, prepared with high reaction rates and in very high yields, were chemically and structurally characterized. These polyols were used for the preparation of rigid polyurethane foams with excellent physical–mechanical properties and inherent flame retardancy. By alkoxylation of isocyanuric polyols with propylene oxide and/or ethylene oxide in a self-catalytic process, odorless polyols with lower hydroxyl numbers and lower viscosities were obtained, leading to PU foams with good properties, but without inherent flame retardancy. The synthesized polyols with isocyanuric structure are suitable for the preparation of all types of rigid polyurethane foams, including thermoinsulation of freezers, buildings, storage tanks and pipes for the food and chemical industry, for packaging, and as wood substitutes.

Preliminary Mechanical Characterization of Reinforced Rigid Polyurethane Foams

2003 ◽  
Author(s):  
Nagesh Kasichainula ◽  
Sanjeev K. Khanna
Keyword(s):  
Mechanical Properties ◽  
Glass Fibers ◽  
Tensile Modulus ◽  
Compression Modulus ◽  
Layered Composite ◽  
Polyurethane Foams ◽  
Rigid Polyurethane Foams ◽  
Structural Applications ◽  
Glass Fiber Reinforcement ◽  
Static Mechanical

Rigid polyurethane foams are very widely used in a variety of structural and non-structural applications. For example, it may be used as an insulator, in sandwich layered composite panels, and as filler for improving the stiffness of lightweight components, such as thin metal tubes. Rigid foams do not show any recovery after impact and typically are crushed or crumble. They also tend to degrade over a period of time. Thus in this investigation, reinforced rigid polyurethane foams have been developed and characterized for their quasi-static mechanical properties. Rigid polyurethane foam was reinforced with short, 0.47 mm length, milled E-glass fibers. It has been observed that short glass fiber reinforcement helps in improving the mechanical properties, such as tensile modulus, breaking strength, and compression modulus, of the reinforced foam as compared to monolithic foam.

scholarly journals Chemically Functionalized Cellulose Nanocrystals as Reactive Filler in Bio-Based Polyurethane Foams

Polymers ◽  
2021 ◽  
Vol 13 (15) ◽  
pp. 2556
Author(s):  
Francesca Coccia ◽  
Liudmyla Gryshchuk ◽  
Pierluigi Moimare ◽  
Ferdinando de Luca Bossa ◽  
Chiara Santillo ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cellulose Nanocrystals ◽  
Aqueous Media ◽  
Polyurethane Foams ◽  
Coupling Agents ◽  
Ftir Analysis ◽  
Thermal And Mechanical Properties ◽  
Efficient Coupling ◽  
Flexible Polyurethane ◽  
Pu Foams

Cellulose Nanocrystals, CNC, opportunely functionalized are proposed as reactive fillers in bio-based flexible polyurethane foams to improve, mainly, their mechanical properties. To overcome the cellulose hydrophilicity, CNC was functionalized on its surface by linking covalently a suitable bio-based polyol to obtain a grafted-CNC. The polyols grafted with CNC will react with the isocyanate in the preparation of the polyurethane foams. An attractive way to introduce functionalities on cellulose surfaces in aqueous media is silane chemistry by using functional trialkoxy silanes, X-Si (OR)3. Here, we report the synthesis of CNC-grafted-biopolyol to be used as a successful reactive filler in bio-based polyurethane foams, PUFs. The alkyl silanes were used as efficient coupling agents for the grafting of CNC and bio-polyols. Four strategies to obtain CNC-grafted-polyol were fine-tuned to use CNC as an active filler in PUFs. The effective grafting of the bio polyol on CNC was evaluated by FTIR analysis, and the amount of grafted polyol by thermogravimetric analysis. Finally, the morphological, thermal and mechanical properties and hydrophobicity of filled PUFs were thoughtfully assessed as well as the structure of the foams and, in particular, of the edges and walls of the cell foams by means of the Gibson–Ashby model. Improved thermal stability and mechanical properties of PU foams containing CNC-functionalized-polyol are observed. The morphology of the PU foams is also influenced by the functionalization of the CNC.

scholarly journals Compressive Behavior of Aluminum Microfibers Reinforced Semi-Rigid Polyurethane Foams

Polymers ◽  
2018 ◽  
Vol 10 (12) ◽  
pp. 1298 ◽  
Author(s):  
Emanoil Linul ◽  
Cristina Vălean ◽  
Petrică-Andrei Linul
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Energy Absorption ◽  
Physical And Mechanical Properties ◽  
Strength Properties ◽  
Polyurethane Foams ◽  
Compression Tests ◽  
Compressive Behavior ◽  
Static Compression ◽  
Pu Foams

Unreinforced and reinforced semi-rigid polyurethane (PU) foams were prepared and their compressive behavior was investigated. Aluminum microfibers (AMs) were added to the formulations to investigate their effect on mechanical properties and crush performances of closed-cell semi-rigid PU foams. Physical and mechanical properties of foams, including foam density, quasi-elastic gradient, compressive strength, densification strain, and energy absorption capability, were determined. The quasi-static compression tests were carried out at room temperature on cubic samples with a loading speed of 10 mm/min. Experimental results showed that the elastic properties and compressive strengths of reinforced semi-rigid PU foams were increased by addition of AMs into the foams. This increase in properties (61.81%-compressive strength and 71.29%-energy absorption) was obtained by adding up to 1.5% (of the foam liquid mass) aluminum microfibers. Above this upper limit of 1.5% AMs (e.g., 2% AMs), the compressive behavior changes and the energy absorption increases only by 12.68%; while the strength properties decreases by about 14.58% compared to unreinforced semi-rigid PU foam. The energy absorption performances of AMs reinforced semi-rigid PU foams were also found to be dependent on the percentage of microfiber in the same manner as the elastic and strength properties.

Lattice Imaging of Grain Boundaries in Ceramics

1977 ◽  
Vol 35 ◽  
pp. 114-115
Author(s):  
D. R. Clarke ◽  
G. Thomas
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Silicon Nitride ◽  
Grain Boundaries ◽  
High Temperature Strength ◽  
Current Interest ◽  
Lattice Imaging ◽  
Special Significance ◽  
Structural Applications ◽  
Refractory Ceramics

Grain boundaries have long held a special significance to ceramicists. In part, this has been because it has been impossible until now to actually observe the boundaries themselves. Just as important, however, is the fact that the grain boundaries and their environs have a determing influence on both the mechanisms by which powder compaction occurs during fabrication, and on the overall mechanical properties of the material. One area where the grain boundary plays a particularly important role is in the high temperature strength of hot-pressed ceramics. This is a subject of current interest as extensive efforts are being made to develop ceramics, such as silicon nitride alloys, for high temperature structural applications. In this presentation we describe how the techniques of lattice fringe imaging have made it possible to study the grain boundaries in a number of refractory ceramics, and illustrate some of the findings.

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