Polyol Component Research Articles

Polyurethane Waste Recycling: Thermolysis of the Carbamate Fraction.

The alcoholysis of polyurethane waste is currently being industrialized, making it one of the most advanced chemical recycling processes for polyurethanes. However, the recycling potential of the dicarbamate phase, which accounts for 10-40% of the polyurethane mass, is often disregarded, as mainly the polyol components are (partially) retrieved in many alcoholysis processes. In this study, we present a two-step recycling method in which the valuable carbamate fraction obtained in the initial alcoholysis step is transformed into an isocyanate-rich mixture through an additional thermolysis step. For this purpose, different carbamates were synthesized and thermolyzed, which showed that thermolysis with isopropyl-carbamate was the most favorable, obtaining a yield of 35%. As a result, the isocyanates obtained through thermolysis and the polyols obtained through alcoholysis can be reused as starting materials in polyurethane synthesis.

Water-Based Polyurethane Dispersions: A Detailed Analysis of the Particle Charge Using Soft and Hard Particle Model.

Water-based polyurethane dispersions (PUDs) show a characteristic dependency of the electrophoretic mobility on the electrolyte concentration, which can be investigated by hard and soft particle models. For this purpose, additional information can be obtained by determining particle charges and electrostatic potentials. PUDs with different contents of an intrinsic ionic stabilizer and various polyol components were synthesized according to the acetone process. The particle charge was characterized by potentiometric acid-base titration, and the data of the titration curve were fitted assuming multiple functional groups with adaptable acid strengths. To investigate the electrostatic potentials, electrophoretic mobilities were measured as a function of electrolyte concentration and analyzed by soft and hard particle theory. Acid-base titration experiments indicated that not all detected ionic groups are located on the surface but are partly arranged inside the polymer particle, as evidenced by a significant decrease of the corresponding effective dissociation constant. The evaluation of the titration data and the electrokinetic experiments showed that the soft particle model of Ohshima is not suitable to reflect the actual particle charge. In contrast, the hard particle model can describe the measured electrophoretic mobility of the dispersions very well if the relaxation effect is taken into account. The dependency of the corresponding zeta potentials on the electrolyte concentration can be excellently modeled assuming a constant surface potential ψ0 and distance of the shear plane xs. Reasonable results are obtained for both parameters with only minor differences between the PUD series. Nonetheless, the electrokinetic surface charge densities calculated with respect to the surface potential are lower than expected from the titration results. Although our results indicate a more complex charge distribution in a peripheral layer, the hard particle model currently shows the best description of the electrokinetic behavior of the PUDs.

Influence of Carboxylic Acid Structure on the Kinetics of Polyurethane Foam Acidolysis to Recycled Polyol.

Closed-loop recycling of plastics is needed to bridge the gap between the material demands imposed by a growing global population and the depletion of nonrenewable petroleum feedstocks. Here, we examine chemical recycling of polyurethane foams (PUFs), the sixth most produced polymer in the world, through PUF acidolysis via dicarboxylic acids (DCAs) to release recyclable polyols. Acidolysis enables recycling of the polyol component of PUFs to high-quality materials, and while the influence of DCA structure on recycled PUF quality has been reported, there are no reports that examine the influence of DCA structure on the kinetics of polyol release. Here, we develop quantitative relationships between DCA structure and PUF acidolysis function for ∼10 different DCA reagents. PUF acidolysis kinetics were quantified with ∼1 s time resolution using the rate of carbon dioxide (CO2) gas generation, which is shown to occur concomitantly with polyol release. Pseudo-zeroth-order rate constants were measured as a function of DCA composition, reaction temperature, and DCA concentration, and apparent activation barriers were extracted. Our findings demonstrate that DCA carboxyl group proximity and phase of transport are descriptors of PUF acidolysis rates, rather than expected descriptors like pK a. DCAs with closer proximity acid groups exhibited faster PUF acidolysis rate constants. Furthermore, a shrinking core mechanism effectively describes the kinetic functional form of the kinetics of PUF acidolysis by DCAs. Measurements of acidolysis kinetics for model PUF (M-PUF) and end-of-life PUF (EOL PUF) confirm the applicability of our analysis to postconsumer materials. This work provides insights into the physical and chemical mechanisms controlling acidolysis, which can facilitate the development of efficient closed-loop PUF chemical recycling schemes.

The Effect of Rapeseed Oil Biopolyols and Cellulose Biofillers on Selected Properties of Viscoelastic Polyurethane Foams.

This paper presents the results of research on polyurethane viscoelastic foams (PUVFs) modified with biomaterials. This investigation looked at the effect of the biomaterials on the foaming processes, as well as the acoustical and selected physical-mechanical properties of the foams. Various types of rapeseed oil biopolyols and microcellulose were used to modify the materials. The analysis of properties covered a reference biopolyol-free sample and materials containing 10 wt.%, 20 wt.%, and 30 wt.% of different types of biopolyols in the mixture of polyol components. The biopolyols differed in terms of functionality and hydroxyl value (OHv). Next, a selected formulation was modified with various microcellulose biofillers in the amount of 0.5-2 wt.%. The PUVFs, with apparent densities of more than 210 kg/m3 and open-cell structures (more than 85% of open cells), showed a slow recovery to their original shape after deformation when the pressure force was removed. They were also characterized by a tensile strength in the range of 156-264 kPa, elongation at break of 310-510%, hardness of 8.1-23.1 kPa, and a high comfort factor of 3.1-7.1. The introduction of biopolyols into the polyurethane system resulted in changes in sound intensity levels of up to 31.45%, while the addition of fillers resulted in changes in sound intensity levels of up to 13.81%.

Strategic design of degradable polyurethanes: Site-specific depolymerization, film-forming behavior, and reprocessability

This paper reports on the rational design of linear sustainable polyurethanes with on-demand depolymerization capabilities and film-forming properties. In this molecular approach, self-immolative urethane motifs are engineered to not only induce rapid degradation in response to an external stimulus via sequential elimination but also provide sufficient inter-chain interactions to yield nanofibers or free-standing films. Amalgamation with various isocyanate or polyol components results in a range of degradable polyurethanes, while doping with europium complexes or carbon black leads to the formation of free-standing hybrid films with photoluminescent or conductive properties, respectively. These films can be reversibly cast using a facile dissolution process, and the predetermined depolymerization products can then be used to generate upcycled materials such as polyurea or polyacrylate films. We believe that our conceptual design for sustainable polyurethanes can be advanced further when combined with conventional engineering techniques to meet industrial and environmental requirements and create desirable materials for contemporary applications.

Vapor-Phase Dicarboxylic Acids and Anhydrides Drive Depolymerization of Polyurethanes.

Polyurethane (PU) is the sixth most used plastic in the world. Because many PU derived materials are thermosets and the monomers are valuable, chemical recycling to recover the polyol component is the most viable pathway to utilizing postconsumer PU waste in a closed-loop fashion. Acidolysis is an effective method to recover polyol from PU waste. Previous studies of PU acidolysis rely on the use of dicarboxylic acid (DCA) in high temperature reactions (>200 °C) in the liquid phase and result in unwanted byproducts, high energy consumption, complex separations of excess organic acid, and an overall process that is difficult to scale up. In this work, we demonstrate selective PU acidolysis with DCA vapor to release polyol at temperatures below the melting points of the DCAs (<150 °C). Notably, acidolysis with DCA vapor adheres to the principles of green chemistry and prevents in part esterification of the polyol product, eliminating the need for additional hydrolysis/processing to obtain the desired product. The methodology was successfully applied to a commercial PU foam (PUF) postconsumer waste.

One‐Step Solvent‐Free Synthesis of Dimer Diamine‐Based Autocatalytic Polyol for the Preparation of Polyurethane Foams

AbstractHerein, this work reports the facile synthesis of a dimer diamine‐based autocatalytic polyol (ACP) and its use in polyurethane foam preparation. The ACP, namely TETRAOL is synthesized in one step, without using solvent, and with 100% atom economy. Additionally, a phosphorous‐modified polyol is synthesized by using 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) and castor oil. In this study, all of the polyol components of the foams are of vegetable oil origin, and amine or tin‐based auxiliary catalysts are not used. The structures of the synthesized autocatalytic polyol as well as other bio‐polyols are characterized by Fourier‐transform infrared (FTIR) and Nuclear magnetic resonance (NMR) spectroscopies. The densities, rise and gel time values, and thermal and mechanical properties of the foams are determined and compared to foams prepared by using a petroleum‐based commercial ACP. The bio‐based TETRAOL‐containing foams display comparable densities and improve thermal properties but longer rise and gel time values concerning the foam prepared by using the commercial ACP.

Toward chemical recycling of PU foams: study of the main purification options.

The recovery of the polyol component, after glycolysis of polyurethane (PU) foams coming from automotive waste, was investigated. Several separation methods such as simple sedimentation, centrifugation and liquid-liquid extraction, eventually preceded by an acid washing step, were tested. The obtained fractions were characterized by infrared spectroscopy and CHN elemental analysis. Furthermore, multivariate data analysis was carried out on the infrared spectra by principal component analysis to classify the fractions based on purity. IR spectroscopy coupled with principal component analysis was able to estimate the success of the separation and eventual culprits such as contaminations, which were then quantified by CHN elemental analysis. This approach addresses some critical limitations associated with classical analytical techniques such as NMR, TGA, GPC, MALDI-TOF that often require an extremely accurate separation of the depolymerized product fractions. Moreover, IR spectroscopy and CHN elemental analysis techniques are cheap and widespread in standard materials science laboratories. At last, based on the results of the analysis of the regenerated polyol fractions, and on the foaming tests, considerations were made to guide the choice of the purification method according to the application specifications and greenness.

Sago starch and esterified sago starch as eco-friendly fillers for rigid polyurethane foams

Novel fillers from sago starch and esterified sago starch were employed as natural fillers for rigid polyurethane foams (RPUFs). Sago starch was esterified by maleic anhydride, resulting in the presence of ester groups on the starch structure. Filled RPUFs were prepared with 0.5-7.0 wt% of starch fillers in the polyol component. The influence of filler type and content on the cell morphology and properties of the RPUFs was analyzed. The results revealed that the esterified sago starch showed better compatibility with polyurethane matrix than the sago starch, which in turn impacted the cellular morphology and physico-mechanical properties of the resulting RPUFs. The density and compressive strength of the RPUFs filled with esterified sago starch were higher than those filled with unmodified sago starch, while their water absorption, and volume shrinkage were lower. The findings also suggested that the compressive strength and density of filled RPUFs increased with starch filler content up to the optimal point and then decreased. This was due to the impact of filler content on cell size, with smaller cell size at low filler content leading to increased strength and density, whereas larger cell size and more open cells at higher filler content reducing strength and density. The best properties were obtained with 1.0 wt% of unmodified sago starch and 0.5 wt% of esterified sago starch in the polyol component.

Fire-Resistant Bio-based Polyurethane Foams Designed with Two By-Products Derived from Sugarcane Fermentation Process

There is a growing interest in replacing conventional fossil-based polymers and composites with waste-based materials and fillers for environmental sustainability. This study designed water-blown polyurethane rigid foams using two by-products from the Amyris fermentation process of producing β-farnesene. The distillation residue (FDR) served as the main polyol component in the foam’s formulation (PF), supplemented with 4.5% sugarcane bagasse ash (SCBA) as a fire-retardant filler (PFA). The study assessed the impact on foam properties. Based on the analysis of all compiled data (foam structure, mechanical, and thermal properties), it can be inferred that ash particles acted as nucleating points in the reaction media, leading to a reduction in foam density (from 134 to 105 kg/m3), cell size (from 496 to 480 nm), and thermal conductivity. The absence of chemical interaction between the ash filler and the polyurethane matrix indicates that the ash acts as a filler with a plasticizing effect, enhancing the polymer chain mobility. As a result, the glass transition temperature of the foam decreases (from 74 to 71.8 ºC), and the decomposition onset temperature is delayed. Although, the incorporation of 4.5% SCBA (grain size below 250 μm) was ineffective in the increment of the compressive strength, that small amount was enough to increase the foam’s specific strength from 1009 to 1149 m2/s2 suggesting that other factors (e.g. polyol feedstock, grain size, ash packing, etc.) are yet to be accounted. The flammability test results indicate that sugarcane bagasse ash improved the foam performance, reducing burning time from 251 to 90 s, time of extinguishment from 255 to 116 s, and burning length from 132 to 56.7 mm, meeting the fire protection standard UL 94, class HB. Despite the need for further improvement and detailed flammability evaluation, the results support the notion that polyurethane foams from renewable waste by-products offer a sustainable alternative to both edible and fossil-based sources. Additionally, sugarcane bagasse ash can be a suitable silica source for reinforcing composites with reduced flammability, potentially replacing harmful halogenated chemicals used for the same purpose.Graphical

The Influence of Soft Segment Structure on the Properties of Polyurethanes.

A series of polyurethanes (PU) were synthesised via one-step polymerisation without a chain extender, using toluene diisocyanate as well as a variety of soft segments composed of different macrodiols. Poly(D,L-lactide) (PDLLA) and polycaprolactone diol (PCL) were synthesised as a polyester type polyols to obtain soft segments. The process of varying the molar ratio of newly synthesised PDLLA in soft segments has been confirmed as a powerful tool for fine-tuning the final properties of PU. Fourier-transformed infrared spectroscopy was used for evaluation of molecular structures of synthesised PDLLA polyol and final PU. Nuclear magnetic resonance spectrometry was used to confirm the presumed structure of PU. The influence of soft segment composition on polyurethane thermal characteristics was examined using thermogravimetric analysis and differential scanning calorimetry. The composition of soft segments had little impact on the thermal stability of PU materials, which is explained by the comparable structures of both polyester polyols. Wide-angle X-ray scattering was utilised to evaluate the effect of amorphous PDLLA on the degree of crystallinity of PCL in soft PU segments. It was discovered that not only did the PDLLA ratio in the soft segment have a substantial influence on the degree of microphase separation in the soft and hard segments, but it also influenced the crystallisation behaviour of the materials. Furthermore, the restriction of crystallisation of the PCL soft segment has been verified to be dependent on the hard segment concentration and the ratio of PDLLA/PCL polyols. The sample with pure PCL as the polyol component achieved the highest degree of crystallinity (34.8%). The results demonstrated that the composition of soft segments directly affected the properties of obtained polyurethane films. These results can be utilised to easily achieve a desirable set of properties required for application in biomaterials.

Effects of low temperatures and high strain rates on the tensile properties of polyurethane polymers for adhesives

ABSTRACT The mechanical properties of polyurethane compounds were experimentally investigated by changing the composition of their components. Polyol components (polyoxypropylene glycol: PPG, polyoxytetramethylene glycol: PTMG, and polycarbonatediol: PCD) were mixed with monomeric methylene diphenyl diisocyanate to synthesize polyurethane pre-polymer, mixed with chain extenders (1,4’-butanediol: 1,4’-BD or dimethylthiotoluene diamine: DMTDA), and cured, to prepare four types of polyurethane resins. Tensile tests were conducted using a mechanical testing machine with a strain rate of approximately 0.3 s−1 and a hydraulic high-speed tensile testing machine with a strain rate of approximately 500 s−1. The temperature was controlled to be −40°C, −10°C, or 25°C. When PTMG was used as the polyol, the stress-strain relationship was less sensitive to temperatures and loading rates, and the material properties exhibited a relatively good balance between elongation and strength. Additionally, the use of 1,4’-BD as a chain extender resulted in higher elongation and lower strength than the use of DMTDA. Conversely, the stress-strain relationship was dramatically altered by the test conditions when PPG and PCD were used as the polyol and embrittlement under a combination of low temperature and high strain rate was confirmed. Furthermore, there were certain compositional combinations that exhibit necking at low temperatures.

Polythionourethane Thermoset Synthesis via Activation of Elemental Sulfur in an Efficient Multicomponent Reaction Approach

For the transition toward a safer and more sustainable production of polymeric materials, new synthetic concepts need to be developed. Herein, we describe a catalytic, solvent-free synthesis approach for novel thionourethane thermoset materials, in which the diisothiocyanate reactant is generated in situ via a sulfurization of isocyanides with elemental sulfur, preventing the exposure and handling of the diisothiocyanate. In this one-pot procedure, castor oil fulfills a dual role: (i) acting as the solvent for the in situ diisothiocyanate synthesis in the first step and (ii) reacting as the polyol component in the subsequent thionourethane thermoset formation. The kinetics of the consecutive two steps were studied in detail via real-time IR measurements, and the thermoset crosslinking step was found to be thermally triggerable after the diisothiocyanate reactant is quantitatively formed, enabling high control over the curing process of the system. Differential scanning calorimetry, thermogravimetric analysis, and rheological measurements were performed to investigate the thermal and mechanical properties of the novel thionourethane thermosets and then compared to analogous polyurethane materials. Our results demonstrate an unprecedented approach for thermoset synthesis via an in situ reagent synthesis, i.e., the generation of isothiocyanates from isocyanides by catalytic activation of elemental sulfur, and subsequent thermally triggerable thermosetting with a polyol, resulting in materials with appealing properties.

Development of biobased polyol from epoxidized soybean oil for polyurethane anti‐smudge coatings

AbstractIn this work, a vegetable oil‐based polyol (ERD) with high hydroxyl value was obtained from ring‐opening reaction between the renewable epoxidized soybean oil and ricinoleic acid, and further esterified with 2,2‐bis(hydroxymethyl)propionic acid. To achieve anti‐smudge coating, the ERD polyol was utilized as the polyol component, hexamethylene diisocyanate trimer was employed as the curing agent, and mono‐hydroxy‐terminated polydimethylsiloxane (PDMS‐OH) was introduced as the low surface energy component. In consequence, the biobased polyurethane anti‐smudge coatings are highly smooth and transparent. With the incorporation of 1 wt% of PDMS‐OH, the obtained coating exhibited superb anti‐ink and self‐cleaning performance. Droplets of water, soy sauce, carbon ink, hexadecane, rice bran oil, and pump oil could slide off the coating surface without leaving any wetting footprints. More importantly, the coating was mechanically robust. Even after the coating was subjected to 2000 writing and erasing cycles with an oil‐based marker pen, it still displayed good ink shrinkage ability and the ink traces could be easily erased. Besides, this anti‐smudge coating retained its good hydrophobicity after being soaked in aqueous solutions with different pH values for 24 h. Therefore, the application of this biobased anti‐smudge coating would offer a lower carbon footprint than its petroleum‐based counterparts.

Optimization of Polyurethane Panels Properties through Different Particle and Fiber Reinforcement

AbstractPolyurethane is a highly versatile material and depending on its structure it can be applied in several application fields. One of its main applications is insulating material for the construction sector, while the most common product shape is the rigid expanded panel. This work investigates the possibility of optimizing polyurethane expanded panels for building insulating purposes by considering different particle and fiber reinforcements. Precisely, the addition of different reinforcement percentages of bentonite, phyllite, and recycled textile microfibers (both untreated and treated with NaOH) is considered in polyurethane mixes composed of isocyanate, polyol, water, silane additive, and catalysts. For fiber reinforced samples, castor oil is additionally considered as a more sustainable polyol component in polyurethane mix. Thermal conductivity is positively reduced by increasing phyllite content; indeed, these microspheres further apport porosity to the material, so a lower density, and promotes a homogeneous, fine, and closed porosity. Besides, both castor oil and NaOH fiber treatment enhance the thermal insulating too. Since insulating materials may find application also in structural elements, stress relaxation, and compression tests are performed. Polyurethanes containing phyllite display greater stiffness and mechanical improvements for specific ranges of particle percentage. On the other hand, the fiber reinforcement exceeds the particle one by an order of magnitude in improving mechanical properties in terms of maximum load and recovery. In conclusion, polyurethane reinforcements and alternative polyols are valuable solutions towards more sustainable and performant insulating building panels and product differentiation.

Open-cell bio-polyurethane foams based on bio-polyols from used cooking oil

Used cooking oil is a widely available and inexpensive waste with a high application potential as a feedstock for the bio-based polyurethane production. Usually, bio-polyols from vegetable oils have higher viscosity and lower hydroxyl values compared to commercial petrochemical polyols, which limits their usefulness. This article reports on the development of open-cell polyurethane foam systems wherein 100% of the polyol components were bio-polyols obtained from used cooking oil. What is particularly considered is the effect of bio-polyol properties (molecular weight, viscosity and hydroxyl value) on the properties of the final open-cell polyurethane systems - apparent density, thermal conductivity coefficient, content of closed cells, mechanical strength, brittleness and short-term water absorption. It was found that the key step in the synthesis of bio-polyols designed for open-cell polyurethane foams is the epoxidation reaction. The epoxy value has a significant effect on the occurrence of side reactions (mainly oligomerization) during the oxirane ring-opening process determining the properties of bio-polyols. The resulting open-cell foams were characterized by apparent densities from 12.4 to 13.3 kg/m3, thermal conductivity coefficients from 36.6 to 38.2 mW/m∙K, and closed cell contents below 10%, which makes them comparable to commercial products. The results demonstrate that used cooking oil-based polyols can provide an alternative starting material for open-cell polyurethane foam production.

Facile fabrication of thermoresponsive polyurethanes including polycarbonate diol for enhanced shape-memory performance

Shape-memory polymers (SMPs) are materials that can recover its original shape from a temporarily fixed shape via external stimuli. Due to their shape-memory effects, SMP-based materials have been investigated for engineering applications in diverse areas. Among various SMP materials, shape-memory polyurethane (SMPU) has been extensively studied. Several studies have modified the morphology of SMPU matrices by incorporating various types of polyol components. In this study, we used two structurally distinct polyol substances, polycarbonate diol (PCD) and polyethylene glycol, to synthesize SMPU. The structures of the SMPU matrix could be tuned by varying the PCD mol% of the total polyol content. Shape-memory and mechanical properties are related to the interactions between the soft and hard segments of the SMPU. The permanent shape of the SMPU can be redefined by utilizing the shape-reconfigurable nature of transcarbamoylation. The redefined permanent shape can also be recovered from the temporarily deformed shape through shape-memory cycles.

Unexpected Random Copolymerization of Propylene Oxide with Glycidyl Methyl Ether via Double Metal Cyanide Catalysis: Introducing Polarity in Polypropylene Oxide

The synthesis of amorphous, polar aliphatic polyethers based on the copolymerization of propylene oxide (PO) and glycidyl methyl ether (GME) is described. Copolymers with Mn of 1.9–4.5 kg mol–1, with moderate to low dispersities (D̵ < 1.29) and up to 45 mol % GME content, were obtained via double metal cyanide (DMC) catalysis. An in-depth investigation of the solvent-free copolymerization was conducted by pressure monitoring, in situ 1H NMR spectroscopy, and 13C NMR triad analysis. Surprisingly, the results reveal an almost ideally random copolymerization of both epoxides (rPO = 1.40 ± 0.01, rGME = 0.71 ± 0.01). This observation is in pronounced contrast to the well-known preferential incorporation and generally high reactivity of PO in DMC catalysis in comparison to other epoxide monomers as well as the considerably lower reactivity of PO in the anionic ring-opening polymerization compared to glycidyl ethers. The reactivity ratios were evaluated at both 60 and 80 °C, demonstrating the reproducibility of the utilized solvent-free in situ measurement, showing also the temperature independence of the reactivity ratios within this range. Supplementary 13C NMR triad analysis further supports an almost ideally random copolymerization, confirming an evenly distributed incorporation of polar GME units in the hydrophobic PPO backbone. Turbidimetric measurements demonstrate tunable thermoresponsive behavior and hydrophilicity of the synthesized copolymers with lower critical solution temperatures between 19 and 35 °C. Furthermore, the increase of hydrophilicity is illustrated by contact angle measurements. The random copolymerization of PO and GME by DMC catalysis renders the resulting flexible polyethers an alternative to established ethylene oxide/PO copolymers for flexible polyol components in soft polyurethane foams.

Palm Oil Based Water-Resistant Coating using Pre-Polymer Method

The paper presents some results on the ability of palm oil polyol to replace the petroleum-based polyol in polyurethane (PU) synthesis. In this study, palm oil polyol with amine functionality with hydroxyl value (OH value) between 240 -253 mg KOH/g was used as the polyol component to replace the conventional petroleum-based polyol. Four different formulationsof polyurethane coating have been prepared using pre-polymer process namely PU1, PU2, PU3 and PU4 with the polyol to isophorone diisocyanate ratio (OH:NCO) of 1:0.6 and 1:0.5 and acetone within 25-50 wt %. PU1 (1:0.6) and PU2(1:0.5) result in brittle film, while PU3 (1:0.6) and PU4 (1:05) has a soft and flexiblefilm with better transparency. This finding establishes that the acetone content effect the final properties of the polyurethane formed. The polymerization reaction was monitored using thefourier transform infra-red spectroscopy and it was found that the peak correspondsto NH (3302 cm-1), CO (1627 cm-1) and CN (1543 cm-1) stretching of urethane linkage appearingin all the PU films. The water uptake test was done on the films and it was found that the percentage of water uptake is less than 5% within 24 hours of immersion.The surface morphology of the PU films shows thathomogeneitywas achieved in 1:0.6 of OH:NCO ratio with 25 wt% of acetone. The PU films havethe potential to be developed for water resistant coating.

The effect molecular weight of polyol components on shape memory effect of epoxy‐polyurethane composites

AbstractThis paper describes the experimental findings of the study of a series of PU/epoxy composites, which formed interpenetrating networks and have shape‐memory properties. The morphological variation for different chemical compositions and the influences of morphology on mechanical performance and shape‐memory behavior are discussed. Length and mass fraction of polyethylene glycol (PEG) units are chosen as the key parameters in this study. The molecular weight of PEG was varied from 400 (as such PEG units are unable to crystallize) to 1500, 4000, and 6000, which are crystallizable. It was shown that the crystallization of PEG units is the key parameter, which determines the mechanical performance and shape‐memory behavior of PU/epoxy composites in this study. DMTA results show the linear dependence of glass transition temperature and tensile strength, elongation, and other mechanical parameters on the amount of PEG in PU/epoxy composites independently of the amount of PEG unit lengths. The maximal value of shape fixation rate was achieved for 30–40 mass percentage of PEG 4000 (4.5 × 10−2 s−1 at Tg + 20°C) or PEG 6000(4.1 × 10−2 s−1 at Tg + 20°C) in PU/epoxy composites.