2002 Annual Report
Research
Modulus Development During Foam Formation
Mrinal Bhattacharya, Professor
Ajay Pal Singh, Graduate Student
Funding Source
Urethane Soy Systems
Objective
Modified soy-based vegetable oil polyols have been successfully incorporated
as a replacement for synthetic polyols to produce flexible slabstock polyurethane
foams. While the rheology of reacting polyurethane foams from synthetic
polyols has been investigated, no work has been done to study the rheology
of reacting polyurethane foams from soy polyols. The objective of this
study was to investigate the modulus development during foam formation
using soy polyol.
Project Description
The study of rheological changes during the foam reaction is important
in design and optimization of such a process. In this work the foam, based
upon soy polyol and a 50:50 mixture of TDI:MDI, was monitored for modulus
development. The effect of various ingredients, such as water and isoyanate
index, and addition of OH groups was studied. A vane fixture was used
in an ARES strain controlled rheometer. A four-blade vane was fabricated
using four microscope slides fused onto a glass rod as the center shaft.
A stiff paper bucket was used as the container for the foam rise. The
modulus development of the reacting foam was monitored at 1 rad/s and
0.1% strain.
Results
A four–stage modulus development profile was observed: initial bubble growth, bubble network, polymer stiffening and final curing. This profile was similar to the profile for foams from synthetic polyol (voranol), but different in that the time for each stage was prolonged in the case of soyol foams due to the slow rise. Elastic modulus (G’) and viscous modulus (G”) increased with increasing water content and decreased with decreasing isocyanate index. The modulus development was found to be frequency-independent for 1, 10 and 20 rad/s. The rate of reaction or the rise of the foam was slow for the soyol foam as compared to the synthetic polyol. This is because polyols with primary OH end-groups are the most reactive and they react with isocyanate about 10 times faster than similar polyols with secondary OH groups. Addition of synthetic polyol therefore decreased the modulus and increased the rate of reaction. Ozonization of soybean oil decreased the modulus without affecting the reaction rate, but there was no significant difference between the modulus for 3hr and 5hr ozonized samples. SEM studies were done for the final cured foams. It was found that the cell size increased with increased water content. Size and shape of the cells was less uniform for soyol foams as compared to the synthetic foams. However, the uniformity in size and shape for soyol foams improved with ozonization, probably due to the addition of secondary OH end-groups. Soyol foams have fewer open cells than the synthetic foams, which conforms to their higher modulus.