Journal of Cellular Plastics

The North American appliance industry has been challenged to meet stringent federal standards for energy consumption using CFC alternatives, which generally increase thermal conductivity of a foam. After a period of evaluating several options, the industry has, for the most part, settled on hydrochloro-fluorocarbon, HCFC-141b, as a substitute for CFC-11. Studies have shown that appliance foam systems using carbon black in conjunction with HCFC-141b lower k-factors by 6-9% both in panels and in cabinets.

Recent efforts in this area have demonstrated that this approach not only lowers k-factors but can provide benefits to reduce energy consumption of refrigerator cabinets.

Preliminary evaluation of carbon black-containing foams based on HCFC-141b had shown that the material processed well in cabinets and had no effect on linear appearance. No modifications to the foam processing equipment was necessary. Since black dispersions are relatively higher in viscosity compared to conventional isocyanates, a process study was conducted to understand flow behavior and maximize foam performance in cabinets.

Handmix work was extended to cyclopentane systems. Studies have shown that improvements of 7-9% in k-factors can be obtained in foams containing carbon black. This work demonstrates the versatility of using carbon black with different blowing agents. The use of carbon black provides an additional means of improving thermal insulation of polyurethane foam produced with current technologies.

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.

The amount and distribution of blowing agent in rigid polyurethane foam were determined by several methods, which are described and compared. A method for solvent extraction with subsequent gas chromatographic analysis was developed and found to be advantageous for CFC-blown foam along with a combustion method (the Schoniger method), where the chloride ions formed were determined by titration. The solvent extraction method was successfully applied to blowing agents in CFC-free foams as well. Three methods involving heating and weight-loss determination were evaluated. They are easy to use, but corrections for thermal decomposition of the polymer are needed. About half of the total amount of CFC-11 in the investigated polyurethane foams from district heating pipes was found to be dissolved in the polymer matrix.

The refrigerator industry is faced with regulatory pressure on the one hand to replace CFCs as the blowing agent used in insulative foams and on the other to dramatically increase the energy efficiency of refrigerators by 1998. One of the solutions proposed is the use of vacuum panels as insulating components in the walls of the refrigerator. A variety of materials have been proposed as filler materials for the interior of such panels. A novel class of materials recently developed by Dow Plastics for this application is microcellular polyurea xerogels. These xerogels have been prepared by polymerizing polymeric MDI in solution to provide microcellular materials with pore sizes of about 10 microns and surface areas of about 98 sq meter/gram. Conventional open cell rigid foams, by contrast, have cell sizes of about 120 microns and surface areas of about 0.1 sq meter/gram. Polyurea xerogels represent an alternative filler for vacuum panels to precipitated silica or other inorganic powders, providing lower thermal conductivity under vacuum, lower density (6.5 to 8 pcf versus 12.5 pcf for precipitated silica), and potentially reduced vacuum panel fabrication costs (due to their monolithic form and elimination of powder handling). These microcellular materials were characterized by DMS (dynamic mechanical spectroscopy), DSC (differential scanning calorimetry), TGA (thermal gravimetric analysis) and SEM (scanning electron microscopy). Laboratory scale vacuum panels have been fabricated and thermal conductivities measured. Greater flexibility in vacuum panel fabrication and part integration may be possible due to the ability of these materials to be machined or potentially molded into shapes. Additionally, unlike the technically mature area of open cell rigid foams, which have historically exhibited a lower pore size limit of approximately 50 microns, the potential exists for further pore size reduction in polyurea xerogels (currently at about 10 microns). As pore size is reduced in these novel materials, the corresponding thermal conductivity performance will improve.

Increasingly, the automotive industry is requiring demonstration that polymers in automotive applications are recyclable.

The techniques for the recovery and recycling of polyurethane foam from MDI Pour-in-Place automotive seating have been demonstrated. This seating technology is uniquely suited to the recovery of foams for physical and chemical recycling.

The pulverization of flexible foam and its physical recycling back into automotive seating is described with estimations of the costs involved and performance of the resulting product. Recent work on the chemical recycling of MDI automotive seating is outlined.