Crosslinking density and its effect on the dynamic mechanical properties of rigid polyurethane foams

A novel method to generate time–temperature–transformation (TTT) diagrams from Differential Scanning Calorimetry (DSC) data is presented. The methodology starts with dynamical DSC information to obtain the total transformation heat, followed by an isothermal‐dynamic temperature ramp that allows the inclusion of diffusion‐controlled reaction kinetic. The cure kinetics is modeled using an auto‐catalytic Kamal–Sourour model, complemented with a Kissinger model that allows the direct prediction of one energy of activation, DiBenedetto's equation for the glass transition temperature as a function of the cure degree and adjusted reaction constants to include diffusion mechanisms. The methodology uses a nonlinear least‐squares regression method following J.P. Hernández‐Ortiz and T.A. Osswald's methodology (J. Polym. Eng. 2004, 25, 23). A typical linseed epoxy resin (EP) presents two different kinetics control mechanisms, thereby providing a good model to validate the proposed experimental and theoretical method. TTT diagrams for EPs at two different accelerator concentrations are calculated from direct integration of the kinetic model. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40566.

Section: Introductionmentioning

confidence: 99%

Method for time–temperature–transformation diagrams using DSC data: Linseed aliphatic epoxy resin

Restrepo-Zapata

Osswald

Hernández-Ortíz

2014

“…PU foams are usually synthesized by reacting diisocyanate with polyol in presence of catalyst, blowing agent, and surfactant to achieve the desired morphology. Foam properties are direct consequence of its chemical structure and cross‐link density 3,4 . Both functionalities of isocyanate and hydroxyl number of polyol can alter the cross‐link density of polymer network, and higher number of functionalities lead to more rigid structure 3 .…”

Section: Introductionmentioning

confidence: 99%

Role of additives in fabrication of soy‐based rigid polyurethane foam for structural and thermal insulation applications

Bose

Dhaliwal

Chandrashekhara

et al. 2021

Environmental concerns continue to pose the challenge to replace petroleum‐based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy‐based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum‐based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone‐based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m2·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy‐based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum‐based foam Baydur 683.

“…Understanding cure kinetics of thermosets, including epoxies, is critical to continue the advancement of lightweight manufacturing with prepreg materials . Spectrochemical, mechanical, and thermal analyses have all been used to monitor curing reactions. One of the most common, which dates back to the 1960s is differential scanning calorimetry (DSC), which measures the heat released during the exothermic reaction from which both the cure rate and the degree of cure as a function of time and temperature can be determined.…”

Section: Introductionmentioning

confidence: 99%

Quasi‐isothermal DSC testing of epoxy adhesives using initial fast heating rates

Puentes

Restrepo-Zapata

Chaloupka

et al. 2017

Three major factors decrease the accuracy of the cure measurement in standard-isothermal testing using differential scanning calorimetry (DSC). First, cure occurs during the heating step. Second, data are lost during the stabilization period between the dynamic and isothermal step. Third, the baseline selection requires a modification to the protocol. An alternative, which is explored in this study, is the use of fast ramps, which decrease the heating time, but this has been avoided due to overshoot that occurs between the dynamic and isothermal step, which is troublesome for systems with autocatalytic kinetics. By mitigating these factors, a quasi-isothermal protocol was developed. Therefore, more complete cure kinetics were captured with the implementation of fast DSC to decrease the ramp time and through the optimization of furnace parameters to decrease stabilization time and temperature overshoot. The data suggested this quasi-isothermal analysis more accurately measured the isothermal curing kinetics of a commercial epoxy adhesive at 110, 115, and 120 8C for fast ramps of 175, 350, and 500 K/min compared to the traditional ramp of 5 K/min. The enthalpy spike at the dynamic to isothermal transition remains an issue; however, an empirical shift can be used to compensate for the enthalpy signal lag.