(3) HFO/HCFO
In recent years, domestic and foreign organic fluorine chemical enterprises have been actively looking for and developing new fluorine-containing physical blowing agent, fluorinated olefin (HFO) blowing agent, known as the fourth generation of blowing agent, is a physical blowing agent with good gas phase thermal conductivity and environmental benefits. China’s organic fluorine chemical enterprises are also actively developing HFO-based blowing agents, and Quanzhou Yuji New Material Co., Ltd. has independent intellectual property rights of HFO-based products of Chinese companies. One of them is HFO-1233ze(E) (trans-1-chloro 3,3,3-trifluoropropene), an environmentally friendly blowing agent, which was patented in 2006 and will start production in the first quarter of 2023.
Formulation application work in the polyurethane panel sector and in the spray industry (PU and PIR foams) has shown that the blowing agent can be simply replaced in existing formulation systems or fine-tuned to meet the requirements of the foaming process and foam properties. The thermal conductivity of the foams produced has a lower thermal conductivity and a higher yield than HFC-245fa in a certain temperature range. For economic reasons, blending with other blowing agents can be considered, usually in combination with pentane and 245fa.
At present, there are problems with the high cost of using HFO-1233ze(E) alone in spray systems. The foaming agent has been used in countries such as the USA, Europe, Japan and the Philippines.
HFO-1336mzzZ is also an environmentally friendly blowing agent with the chemical name cis-1,1,1,4,4,4-hexafluoro-2-butene and the molecular structure formula CFCH=CHCF. Its production plant is located in Quanzhou City, Fujian Province and is scheduled to be launched on the market in the first half of 2023.
As a polyurethane blowing agent, HFO-1336mzzZ has a moderate boiling point, comparable to HCFC-141b; low thermal conductivity, close to HCFC-141b; zero ODP value and low GWP value; non-combustible, high safety performance; low toxicity, not a VOC substance.
Formulation application research shows that HFO-1336mzzZ is easy to use and can directly replace the blowing agent in the original formulation, as HFO-1336mzzZ has good solubility to polyether raw materials, which may only bring about a reduction in material viscosity and an increase in fluidity. This may be attributed to its higher molecular weight, which makes it difficult to escape from the foam pore structure.
Currently, the economics of HFO-1336mzzZ is still an issue, while the higher molecular weight of HFO-1336mzzZ (164 relative molecular mass) requires a higher dosage of blowing agent during the replacement process, further leading to higher costs. A viable solution for the future is to combine it with a cheaper, environmentally friendly blowing agent.
At present, the foaming agent has been used in spraying, refrigerators, with good thermal insulation properties and good physical properties.
(4) Methyl formate and methylal
The use of methylal in the manufacture of polyurethane foam to replace HCFC-141b appears to be a viable solution that achieves all the objectives of a cost-effective, zero ODP, low GWP replacement technology. The final performance of the foam was comparable to that of HCFC-141b-based foams, after assessing the application of methylal in polyurethane foams. The results of the performance tests were satisfactory. However, due to the low flash point of methylal, its irritating odour and some toxicity, there is less research on its application.
Methyl formate the blowing agent has lower molecular weight and better environmental benefits, higher boiling point and safety than methylal, has a price comparable to HCFC-141b, but has a higher price cost advantage due to its lower molecular weight.
Methyl formate as a physical blowing agent, low production cost, low molecular weight, low thermal conductivity of the gas phase and its strong foaming effect, and good compatibility with the components in the combination of polyether, is one of the HFC class of fluorocarbon blowing agent alternative blowing agent options. Since the 1990s, applied research on methyl formate has been carried out. However, the performance of polyurethane rigid foam prepared with methyl formate as the main physical blowing agent was not very satisfactory, especially the dimensional stability of the foam was very poor, when methyl formate was mixed with other blowing agents (pentane series or methylene chloride), the dimensional stability of the prepared foam was good. Afterwards, people have studied the use of methyl formate mixed with HFCs, HFOs and other fluorocarbon blowing agents to prepare rigid polyurethane foams.
In summary, a number of alternative technology options have been developed with the development of ODS alternatives. Among them, HFO/HCFO technology, with the widespread use in the application, makes the domestic HFO market expand year by year; and methyl formate in the formulation of a small amount of moderate price, the economy is more suitable, but considering its own physical characteristics, need to work on the formulation design. The breakthrough point for seeking technical and economic balance may be the adoption of a composite foaming agent technology route.
