scholarly journals Nanoparticles Addition in PU Foams: The Dramatic Effect of Trapped-Air on Nucleation

Polymers ◽  
2021 ◽  
Vol 13 (17) ◽  
pp. 2952
Author(s):  
Beatriz Merillas ◽  
Fernando Villafañe ◽  
Miguel Ángel Rodríguez-Pérez
Keyword(s):  
Polyurethane Foams ◽  
Nucleation Density ◽  
Atmospheric Conditions ◽  
Manufacturing Method ◽  
Trapped Air ◽  
Cell Nucleation ◽  
Magnetic Stirring ◽  
Pu Foams ◽  
Different Levels ◽  
Nucleating Effect

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 conditions with magnetic stirring. The samples thus obtained were characterized, and the effect of trapped air into the reactive mixtures was evaluated by analyzing the cellular structures. Different levels of trapped air were achieved when employing each manufacturing method. A correlation between the trapped air and the increase in the nucleation density when nanoclays were added was found: the cell nucleation density increased by 1.54 and 1.25 times under atmospheric conditions with electric and magnetic stirring, respectively. Nevertheless, samples fabricated without the presence of air did not show any nucleating effect despite the nanoclay addition (ratio of 1.09). This result suggests that the inclusion of air into the components is key for improving nucleation and that this effect is more pronounced when the polyol viscosity increases due to nanoclay addition. This is the most important feature determining the nucleating effect and, therefore, the corresponding cell size decreases.

scholarly journals Effect of the Molecular Structure of TPU on the Cellular Structure of Nanocellular Polymers Based on PMMA/TPU Blends

Polymers ◽  
2021 ◽  
Vol 13 (18) ◽  
pp. 3055
Author(s):  
Ismael Sánchez-Calderón ◽  
Victoria Bernardo ◽  
Mercedes Santiago-Calvo ◽  
Haneen Naji ◽  
Alberto Saiani ◽  
...  
Keyword(s):  
Cell Size ◽  
Cellular Structure ◽  
Thermoplastic Polyurethane ◽  
Nucleating Agent ◽  
Nucleation Density ◽  
Cell Size Distribution ◽  
Cell Nucleation ◽  
Hard Segments ◽  
Different Characteristics ◽  
Nucleating Effect

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 polymers based on PMMA have been produced by gas dissolution foaming using TPU as a nucleating agent in different contents (0.5 wt%, 2 wt%, and 5 wt%). TPU characterization shows that as the content of HS increases, the density, hardness, and molecular weight of the TPU are higher. PMMA/TPU cellular materials show a gradient cell size distribution from the edge of the sample towards the nanocellular core. In the core region, the addition of TPU has a strong nucleating effect in PMMA. Core structure depends on the HS content and the TPU content. As the HS or TPU content increases, the cell nucleation density increases, and the cell size is reduced. Then, the use of TPUs with different characteristics allows controlling the cellular structure. Nanocellular polymers have been obtained with a core relative density between 0.15 and 0.20 and cell sizes between 220 and 640 nm.

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.

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.

Compression Characterization of Polyurethane Foams with Different Formulations of Polyol and MDI

2015 ◽  
Vol 815 ◽  
pp. 74-78
Author(s):  
Sinar Arzuria Adnan ◽  
Firuz Zainuddin ◽  
Hazizan Md. Akil ◽  
Sahrim Hj Ahmad
Keyword(s):  
Compressive Strength ◽  
Energy Absorption ◽  
Palm Oil ◽  
Polyurethane Foams ◽  
Methylene Diphenyl Diisocyanate ◽  
Pu Foams

Rigid polyurethane (PU) foams were prepared with palm oil based polyols (POP) and methylene diphenyl diisocyanate (MDI) in order to archieve rigid formulations. The effect of the different amount of MDI (1 wt.%, 1.1 wt.% and 2 wt.%) were studied in density, compressive strength and energy absorption. It was found that the higher compressive strength of the PU foams showed at 1.604 MPa whereas the amount of MDI increased to 1.1 wt. %. The increased amount of MDI to 2 wt.% showed the higher value in density (0.0531 kg/m3) and energy absorption with 46.490 J for 70 % displacement.

scholarly journals Some Key Factors Influencing the Flame Retardancy of EDA-DOPO Containing Flexible Polyurethane Foams

Polymers ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1115 ◽  
Author(s):  
Agnieszka Przystas ◽  
Milijana Jovic ◽  
Khalifah Salmeia ◽  
Daniel Rentsch ◽  
Laurent Ferry ◽  
...  
Keyword(s):  
Flame Retardancy ◽  
High Speed ◽  
Combustion Efficiency ◽  
Polyurethane Foams ◽  
Key Factors ◽  
Ul 94 ◽  
Microscale Combustion Calorimeter ◽  
Flexible Polyurethane ◽  
Combustion Calorimeter ◽  
Pu Foams

The role of various additives (emulsifier, anti-dripping agent) and formulation procedures (pre-dispersion of solid additives in polyol via milling) which influence the flame retardancy of 6,6′-[ethan-1,2-diylbis(azandiyl)]bis(6H-dibenzo[c,e][1,2]oxaphosphin-6-oxid) (EDA-DOPO) containing flexible polyurethane foams has been investigated in this work. For comparison, the flame retardancy of two additional structurally-analogous bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based compounds, i.e., ethanolamine-DOPO (ETA-DOPO) and ethylene glycol-DOPO (EG-DOPO) were also evaluated together with EDA-DOPO in flexible PU foams of various formulations. The flame retardancy of these three bridged-DOPO compounds depends on the type of PU formulation. For certain PU formulations containing EDA-DOPO, lower fire performance was observed. Addition of emulsifier and polytetrafluoroethylene (PTFE) to these PU formulations influenced positively the flame retardancy of EDA-DOPO/PU foams. In addition, dispersion of EDA-DOPO and PTFE via milling in polyol improved the flame retardancy of the PU foams. Mechanistic studies performed using a microscale combustion calorimeter (MCC) and its coupling to FTIR showed no difference in the combustion efficiency of the bridged-DOPO compounds in PU foams. From MCC experiments it can be concluded that these bridged-DOPO compounds and their decomposition products may work primarily in the gas phase as flame inhibitors. The physiochemical behavior of additives in PU formulation responsible for the improvement in the flame retardancy of PU foams was further investigated by studying the dripping behavior of the PU foams in the UL 94 HB test. A high-speed camera was used to study the dripping behavior in the UL 94 HB test and results indicate a considerable reduction of the total number of melt drips and flaming drips for the flame retardant formulations. This reduction in melt drips and flaming drips during the UL 94 HB tests help PU foams achieve higher fire classification.

Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

e-Polymers ◽  
2011 ◽  
Vol 11 (1) ◽  
Author(s):  
Fiorenza Azzurri ◽  
Paola Stagnaro ◽  
Lucia Conzatti ◽  
Dario Cavallo ◽  
Luca Repetto ◽  
...  
Keyword(s):  
Shear Flow ◽  
Flow Direction ◽  
Crystallization Rate ◽  
Morphological Characterization ◽  
External Flow ◽  
Nucleation Density ◽  
Induced Crystallization ◽  
Flow Induced Crystallization ◽  
Nucleating Effect

AbstractThe flow induced crystallization behaviour of a LDPE:PE-g-MA:D72T 90:9:1 nanocomposite has been investigated by in-situ Rheo-SALS technique and data have been compared with those obtained from a reference LDPE:PE-g-MA 90:9 sample. Rheo SALS results, confirming thermal analysis findings, indicate that under mild shear flow fields the organoclay exhibits a negligible nucleating effect. Both nucleation density and, as a consequence, crystallization rate, are not appreciably affected by the application of external flow field for both the examined systems, revealing that no evident synergic effects between the organoclay and the shear flow are present. On the other hand, Rheo SALS analysis indicates that the nanocomposite submitted to flow exhibits a higher level of crystal orientation. TEM morphological analyses support this observation suggesting that the orientation of the nanofiller along the flow direction templates the growth of oriented crystals.

scholarly journals The Effects of Various Additive Components on the Sound Absorption Performances of Polyurethane Foams

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Shuming Chen ◽  
Yang Jiang ◽  
Jing Chen ◽  
Dengfeng Wang
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Polyurethane Foams ◽  
Acoustic Properties ◽  
Acoustic Absorption ◽  
Absorption Properties ◽  
Maximum Enhancement ◽  
Flexible Polyurethane ◽  
Pu Foams

Flexible polyurethane (PU) foams comprising various additive components were synthesized to improve their acoustic performances. The purpose of this study was to investigate the effects of various additive components of the PU foams on the resultant sound absorption, which was characterized by the impedance tube technique to obtain the incident sound absorption coefficient and transmission loss. The maximum enhancement in the acoustic properties of the foams was obtained by adding fluorine-dichloroethane (141b) and triethanolamine. The results showed that the acoustic absorption properties of the PU foams were improved by adding 141b and triethanolamine and depended on the amount of the water, 141b, and triethanolamine.

scholarly journals Effect of Oxygen Pressure on the Initial Oxidation Behavior of Cu and Cu-Au Alloys

2011 ◽  
Vol 1318 ◽  
Author(s):  
Langli Luo ◽  
Yihong Kang ◽  
Zhenyu Liu ◽  
Judith C Yang ◽  
Guangwen Zhou
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxygen Pressure ◽  
Atomic Scale ◽  
Nucleation Theory ◽  
Nucleation Density ◽  
Atmospheric Conditions ◽  
Initial Oxidation ◽  
Effect Of Oxygen ◽  
Pure Cu

ABSTRACTA wide information gap exists between our present atomic-scale knowledge of metal oxidation derived from conventional ultrahigh vacuum (UHV) surface science experiments and the oxidation mechanisms obtained from the growth of bulk oxide thin films under technologically relevant realistic (or near-) atmospheric conditions. To bridge this pressure gap, we present an in-situ transmission electron microscopy (TEM) study of the initial oxidation stage of Cu(100) and Cu-Au(100) surfaces where the oxygen partial pressure varies from 5x10-4 to 150 Torr. For Cu(100), with increasing oxygen partial pressure (pO2), the nucleation density of the oxide islands increases and so does the growth rate of the oxide islands. As the pO2 continues to increase, a transition from epitaxial cube-on-cube Cu2O islands to randomly oriented oxide islands is observed. A kinetic model based on the classic heterogeneous nucleation theory is developed to explain the effect of oxygen partial pressure on the oxide orientation. It is shown that such a transition in the oxide nucleation orientation is related to the effect of oxygen pressure on the nucleation barrier and atom collision rate. The Cu-Au(111) alloy revealed the same oxygen pressure dependency of the oxide nucleation orientation as pure Cu oxidation.

scholarly journals Physical Properties of Soy-Phosphate Polyol-Based Rigid Polyurethane Foams

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Hongyu Fan ◽  
Ali Tekeei ◽  
Galen J. Suppes ◽  
Fu-Hung Hsieh
Keyword(s):  
Thermal Conductivity ◽  
Compressive Strength ◽  
Thermal Properties ◽  
Water Content ◽  
Polyurethane Foams ◽  
Solid Polymer ◽  
Mechanical And Thermal Properties ◽  
Blowing Agent ◽  
Isocyanate Index ◽  
Pu Foams

Water-blown rigid polyurethane (PU) foams were made from 0–50% soy-phosphate polyol (SPP) and 2–4% water as the blowing agent. The mechanical and thermal properties of these SPP-based PU foams (SPP PU foams) were investigated. SPP PU foams with higher water content had greater volume, lower density, and compressive strength. SPP PU foams with 3% water content and 20% SPP had the lowest thermal conductivity. The thermal conductivity of SPP PU foams decreased and then increased with increasing SPP percentage, resulting from the combined effects of thermal properties of the gas and solid polymer phases. Higher isocyanate density led to higher compressive strength. At the same isocyanate index, the compressive strength of some 20% SPP foams was close or similar to the control foams made from VORANOL 490.

Effects of chain extender in biodegradable polyurethane foams

2014 ◽  
Vol 34 (6) ◽  
pp. 555-559 ◽  
Author(s):  
Sung Moon Kang ◽  
Moo Seok Kang ◽  
Sun Hong Kwon ◽  
Hyun Park ◽  
Byung Kyu Kim
Keyword(s):  
Hard Segment ◽  
Crosslinking Density ◽  
Polyurethane Foams ◽  
Chain Extender ◽  
Toluene Diisocyanate ◽  
Foam Formation ◽  
Buffer Solution ◽  
Biodegradable Polyurethane ◽  
Flexible Polyurethane ◽  
Pu Foams

Abstract Molded flexible polyurethane (PU) foams were synthesized from a starch/petroleum based polyol, 2,4/2,6-toluene diisocyanate (TDI-80), using a one shot method with water as the blowing agent. The effects of chain extender type [starch (S series), diethanolamine (DEA, D series), glycerol (G series)] and content (0, 2, 5, 10 pphr) were extensively studied. The rate of foam formation, density, compression strength, glass transition temperature (Tg) and rubbery modulus of the foam increased with the addition and increasing content of extender. At the same extender content, DEA showed the highest of these properties, while starch showed the lowest. The rate of biodegradation in a buffer solution decreased with the addition of DEA and glycerol, due to the increased crosslinking density and hard segment content, but increased with starch, owing to its biodegradability.

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