Debkumar Bhattacharjee

Flammability Characteristics of CO2 Blown Rigid Polyurethane Spray Foam

In view of the ozone depletion potential of HCFC-141b and other HCFCs, processing challenges with gaseous HFC-134a, and flammability potential with pentanes as blowing agents, significant efforts have been deployed in the development of environmentally friendly, all carbon dioxide blown rigid polyurethane spray foams. These foams are primarily used for the insulation of roofs, storage tanks, vessels, walls and piping. The Mannich base initiated Polyol A, developed by The Dow Chemical Company [1], with viscosity of ∼2000 cps at 77°F and OH# of ∼312 was manufactured using patented technology. This OH# is significantly lower than that of the dominating spray foam polyols (OH# 470). The low viscosity and higher equivalent weight of this polyol are designed to alleviate the processing difficulties of typical carbon dioxide blown spray applied systems. Some of the important requirements in spray systems are the flammability characteristics. Most carbon dioxide blown foams, however, suffer from high heat release, smoke and weight loss in small scale burn tests like the Ohio State University (OSU; ASTM E-906) test when compared to the corresponding results with HCFC-141b as the primary blowing agent. A series of formulations containing Polyol A, aromatic polyester polyols and commercially available fire retardants were evaluated at different isocyanate indices. Flammability properties were determined using a variety of small scale test methods including cone calorimeter and ASTM E-906. In an attempt to understand factors contributing to burn properties, several analytical techniques, such as FTIR (Fourier Transform Infrared Spectrometry), TGA (Thermo-Gravimetric Analysis) and DMS (Dynamic Mechanical Spectroscopy) were utilized. Analysis of the FTIR spectra leads to an estimate of conversion of isocyanate end groups and trimerization reactions where applicable. TGA reflects the chemical stability of the polymer network to thermal decomposition and DMS reflects the physical stability of the polymer network. A correlation of these data with the weight loss data after burning has been investigated. A combination of these techniques leads to a systematic approach for the development of spray polyurethane foams with improved flammability characteristics.

Reduced Density Carbon Dioxide Blown Foam Based on a Novel Polyol Technology

In view of increasing pressure to use environmentally acceptable, nonflammable blowing agents with zero ozone depletion potential in the manufacture of rigid polyurethane foams, there is greater interest in 100% carbon dioxide blown technology. When trichlorofluoromethane (CFC-11) or 1,1-dichloro-1-fluoroethane (HCFC-141b) is replaced by carbon dioxide as the cell gas, the resulting foam, in general, suffers from higher thermal conductivity (k-factor), poorer adhesion and worse flowability leading to higher density. The water level in the formulation can be increased to improve flowability of these systems, but foam with poorer dimensional stability is obtained due to rapid diffusion of carbon dioxide out of the foam. In order to maintain adequate dimensional stability, similar to what is achieved in CFC-11/HCFC-141b blown systems, the water level has to be reduced. This leads to unacceptably higher foam density. In addition, the higher k-factor of the foam is primarily due to higher gas k-factor of carbon dioxide compared to those of CFC-11 and HCFC-141b. This is partially offset by lower radiative contribution arising from finer cell structure of carbon dioxide blown foams. Certain applications, however, are less sensitive to the energy requirement, and a foam with higher k-factor may be acceptable. This paper deals with a design of experiments to yield a foam with good processability and excellent dimensional stability in a variety of conditions, while maintaining the in-place density usually obtained with CFC-11/HCFC-141b blown systems. The key to the success was the development of a novel polyol that led to dimensionally stable foams at higher levels of water. The commercial viability of this technology has been demonstrated by producing actual parts without any equipment modifications.

Study of the Effect of Polyol and Isocyanate Viscosities Upon the Processing and Properties of Rigid Polyisocyanurate Foams Blown with HCFC-141b:

The mandated switch from CFC-11 (trichlorofluoromethane) to HCFC-141b (1,1-dichloro-1-fluoroethane) as a blowing agent for polyisocyanurate insulation foams has required producers of these foams to make numerous formulation changes. The changes have been warranted due to the differing physical properties of HCFC-141b versus CFC-11. These differences include higher boiling point, higher latent heat of vaporization, increased polymer solubility and decreased viscosity of the polyol and isocyanate blends which contain HCFC-141b compared to CFC-11. These differences have led to concerns with the ultimate physical properties of polyisocyanurate foams blown with HCFC-141b as compared to those with CFC-11 blown foams. In particular, the increased solubility of HCFC-141b in the foams polymer matrix has led to a reduction in compressive strength and problems with dimensional stability. This paper deals with Dows efforts at improving foam processing and dimensional stability of these foams with the use of high functional, low equivalent weight polyols and increased viscosity and higher functionality Polymeric MDI (PMDI).