Polyurethane Resin System Research Articles

Development of a Novel Biobased Polyurethane Resin System for Structural Composites

Polyurethanes are gaining increasing interest for their use as structural components subjected to cyclic loads, such as leaf springs. Thermoset polyurethane (PUR) based technology offers some advantages, such as fatigue resistance, low viscosity, and fast curing. However, current PUR formulations present two major drawbacks: their petrochemical origin and high reactivity. The aim of this work was to develop a novel biobased PUR (BIO-PUR) with the required mechanical properties and processability for manufacturing structural composites by resin transfer moulding (RTM). For this purpose, a high functionality and high hydroxyl index castor-oil-based polyol was used combined with a biobased glycerol (BIO-Gly) to increase the crosslinking density and improve the final properties of the BIO-PUR. The viscosity and reactivity of the different systems were studied by means of rheology tests and differential scanning calorimetry (DSC). Thermal and mechanical properties were studied by dynamic mechanical analysis (DMA) and flexural tests. Furthermore, the RTM process of a representative part was simulated and validated through the manufacturing and testing of plates. The properties of the BIO-PUR resin systems were strongly influenced by the addition of biobased glycerol and its effect on the crosslinking density. The combination of a high functionality and hydroxyl index biobased polyol with the biobased glycerol resulted in a high-performance BIO-PUR with the required reactivity and final properties for structural applications.

Effect of the catalyst system on the reactivity of a polyurethane resin system for RTM manufacturing of structural composites

Effect of the catalyst system on the reactivity of a polyurethane resin system for RTM manufacturing of structural composites

Material characterization of a pultrusion specific and highly reactive polyurethane resin system: Elastic modulus, rheology, and reaction kinetics

This study presents a detailed material characterization study of a pultrusion specific polyurethane resin system. Firstly, the chemical behaviour was characterized by utilizing differential scanning calorimetry. The cure kinetics was fitted well to an autocatalytic cure kinetics model with Arrhenius temperature dependency. The resin system did not show any inhibition time. Then, the viscosity evolution was observed using a rheometer. From these measurements, the gelation point was estimated from the criterion of cross-over point of storage and loss modulus curves. The corresponding cure degree of gelation point was found to be 0.79 using the cure kinetics model. The complex viscosity evolution through dynamic scans was predicted well with a cure degree and temperature dependent viscosity model. The elastic modulus and glass transition temperature of fully and partially cured samples were measured by means of DMA in tension mode. A five step cure hardening instantaneous linear elastic model was fitted well to a wide range of cure degree values after gelation. Lastly, the fitted material models were employed in a case study of a typical pultrusion process to visualize the effects of pulling speed on the material property evolution.

Effects of phthalic anhydride polyester polyol on mechanical properties of polyurethane resin system based on polymethylene polyphenyl isocyanate-polypropylene glycol

ABSTRACTIn this paper, a series of two-component polyurethane resins were prepared by using polymethylene polyphenyl isocyanate (PMDI) and polypropylene glycol (PPG400) respectively as hard and soft segment. In order to further increase strength, stiffness and heat resistance of resin system, phthalic anhydride polyester polyol (PAPP) was used as second soft segment. The effects of content, functionality and molecular weight of PAPP on mechanical properties of PMDI-PPG resins were mainly studied. The results indicated comprehensive performance of polyurethane resin was best in the case of employing tri-functionality PAPP with a molecular weight of 400 and 40% content in soft segment. The resulting tensile, flexural and impact strength of polyurethane respectively reached 66.4, 92.0 MPa and 66.1kJ/m2. The tensile and flexural strength of glass fibre-reinforced polyurethane composite respectively reached 465 and 552 MPa. PMDI-PPG/PAPP system thus is expected as a new type of resin matrix used for high-performance polymer composites.

Manufacturing and evaluation of polyurethane composite structural insulated panels

Composite materials are increasingly used in applications of civil infrastructure and building materials. The new generations of two-part thermoset polyurethane resin systems are desirable materials for infrastructure applications. This is due to high impact resistance, superior mechanical properties, and reduced volatile organic compounds when compared to the conventionally used resin systems such as vinyl ester and polyester. Glass fiber-reinforced two-part polyurethane composites and low-density polyurethane foam are used to design and manufacture composite structural insulation panels using vacuum assisted resin transfer molding process for temporary housing applications. Using these types of composite panels in building construction will result in cost-efficient, high-performance products due to inherent advantages in design flexibility. Use of core-filled composite structures offers additional benefits such as high strength, stiffness, lower structural weight, ease of installation and structure replacement, and higher buckling resistance than the conventional panels. Energy efficiency is known to be inherently better with the core-filled composite panel than in a metallic material. The panels can be designed to resist the required loads, and the study aims to evaluate the ability of lab scale tests and models to predict part quality in full-scale parts. Furthermore, it discusses the manufacturing challenges. Flexural tests and energy consumption evaluations were performed on these structural components. Finite element simulation results were used to validate the flexural experiment findings.

Manufacturing and Performance Evaluation of Polyurethane Composites Using One-Part and Two-Part Resin Systems

Polyurethane (PU)-based composites show superior performance compared to polyester and vinylester composites. The demand for PU composites is increasing in high technology as well as conventional applications such as infrastructure and automobile. In this study, glass fiber reinforced composite laminates using one-part and two-part PU resin are manufactured using vacuum-assisted resin transfer molding (VARTM) process. A new generation two-part thermoset PU resin system is investigated and compared with commercial one-part PU resin systems. The mechanical performance of glass fiber reinforced composites manufactured using two different PU resin systems is evaluated. Tensile and flexure tests are conducted on both neat resin and glass/PU composites. Low-velocity impact tests are performed on both types of glass fiber reinforced PU composite specimens. Mechanical properties including strength and modulus were measured and analyzed for the two resin systems. Differential scanning calorimetry (DSC) is used to study the cure behavior of both resin systems. A Brookfield LVDV-II programmable rotational type viscometer is employed to study the viscosity profiles of the resin systems. The influence of resin properties on the overall performance of glass fiber reinforced composites is discussed.

Manufacturing and characterization of polyurethane based sandwich composite structures

Demand has been growing for structural systems utilizing new materials that are more durable and require less maintenance during the service lifetime. In particular, sandwich composite structures attract attention due to many advantages such as light weight, high strength, corrosion resistance, durability and speedy construction. In this study, three designs of glass reinforced composite sandwich structures, namely boxes (web-core W1), trapezoid and polyurethane rigid foam, are fabricated using new generation of two-part thermoset polyurethane resin systems as matrix materials with vacuum assisted resin transfer molding (VARTM) process. The stiffness, load-carrying capacity and compressive strength were evaluated. Core shear, flatwise and edgewise compression tests were carried out for these three models. The mechanical response of three designs of sandwich structures under flexural loading were analyzed using commercial finite element method (FEM) software ABAQUS. The simulation results of flexural behavior were validated by experimental findings.

Characterization of polyurethane composites manufactured using vacuum assisted resin transfer molding

Glass fiber-reinforced polymer composites have promising applications in infrastructure, marine, and automotive industries due to their low cost, high specific stiffness/strength, durability, and corrosion resistance. Polyurethane (PU) resin system is widely used as matrix material in glass fiber-reinforced composites due to their superior mechanical behavior and higher impact strength. Glass fiber-reinforced PU composites are often manufactured using pultrusion process, due to shorter pot life of PU resin system. In this study, E-glass/PU composites are manufactured using a low-cost vacuum-assisted resin transfer molding process. A novel, one-part PU thermoset resin system with a longer pot life is adopted in this study. Tensile, flexure, and impact tests are conducted on both the thermoset PU neat resin system and E-glass/PU composites. A three-dimensional finite element model is developed in a commercial finite element code to simulate the impact behavior of E-glass/PU composite for three different energy levels. Finite element model is validated by comparing it with experimental results.

Manufacturing and impact characterization of soy-based polyurethane pultruded composites

Composites have several advantages such as high corrosion resistance, high strength to weight ratio, and lower maintenance costs over conventional materials. The major cost drivers for composites are raw materials and manufacturing process. Automated manufacturing processes like pultrusion and low cost raw materials can significantly lower the cost of composites. Polyurethane (PU) resin systems are commonly used in the pultrusion industry as they have higher performance characteristics and manufacturing feasibility when compared to conventional resin systems such as polyester and vinyl ester. Manufacturing cost can be further decreased by the use of bio-based materials such as soy-based resin systems. In the present work, solid pultruded panels have been manufactured using the base PU and two soy-based PU resin systems. Pultruded panels were subjected to low velocity impact testing. Soy-based PU resin systems showed comparable properties to that of the base PU resin system and is a viable alternative to the conventional petroleum-based PU. POLYM. COMPOS., 35:1070–1077, 2014. © 2013 Society of Plastics Engineers

Carbon nanotube-polyurethane nanocomposites for structural vibration damping

Nanotechnology is an area which has vast potentials for turning fundamental research into successful innovations. In the present paper, damping in Polyurethane (PU)–Multiwalled carbon nanotube (MWNT) nanocomposites is studied by Dynamic Mechanical Analysis (DMA) and Free Layer Damping (FLD) methods. MWNT is functionalised using HNO3/H2SO4 mixture, thionyl chloride and ethylene diamine to introduce amide groups on the nanotube surface. Composites are prepared from a two–part PU resin system and the functionalised MWNT. The work addresses the concept of damping from molecular level interactions using DMA to an actual vibration damping technique, namely FLD. DMA study clearly shows a 70% increase of loss tangent of the nanocomposites as compared to neat PU, indicative of the high damping efficacy. The effectiveness of the developed nanocomposite is established by FLD measurements wherein a good damping of the order of 5–15 dB is observed in the frequency range of 10–1000 Hz, over that of neat PU. The added advantage of the system is the damping capability in the low frequency region also. The study is expected to be helpful in finding damping applications in aircraft and missile substructures, ships and submarines, machinery supports, mounting platforms of electronic equipment, bridges, buildings, etc.

Properties of natural fiber composites made by pultrusion process

Great efforts are being made at Brunel University, UK in attempt to develop natural fiber composites with desired structure and good overall properties for construction. This work focuses on the mechanical and morphological characterization of the pultruded composite rods made from hemp and wool fiber reinforcements. The results showed that the composite using polyurethane resin system has higher specific tensile and compressive strength as well as the Young's and compressive moduli compared with the polyester and vinyl ester composites, while the polyester composite exhibits better flexural strength. The SEM observation of the cross section and layered polyester and polyurethane composites has found defects on the interface of fibers and resin matrix. It is also revealed that fibers are not evenly distributed in the composites and more resin aggregates in areas close to rod surface. Meanwhile, voids have been noticed existing in both composites, but more of them are found in the polyurethane-matrix rod, which correlated to the higher water absorption for this composite.

Synthesis and characterization of cryogenic adhesives based on epoxy‐modified polyurethane resin systems

AbstractPolyurethane adhesives containing the polyether backbone exhibit a good joint strength in cryogenic environments. In practice, many of the commercially available polyurethane adhesive systems contain free or chemically blocked isocyanates which have some limitations. This study presents the synthesis and characterization of a modified polyurethane type adhesive. Glycidol was used to convert the isocyanate‐terminated polyurethane prepolymer to glycidylterminated polyurethane prepolymer. A series of glycidyl‐terminated polyurethanes, based on polyoxypropylene glycol (PPG) soft segments having different molecular weights, were synthesized and their adhesive properties on aluminium were evaluated. The effect of the soft segment length on adhesion was examined.The adhesive properties at room temperature and cryogenic temperature are in line with the phenomenon observed in dynamical mechanical analysis (DMA) and in the phase separation behavior of the polyurethanes. Differential scaning calorimetry (DSC) was used to assess the phase separation content. An improvement in the adhesive strengths at room temperature is achieved by adding epoxy resins to the glycidyl‐terminated polyurethane resins.