# Polyurethane Foaming Technology Polyurethane (PU) is a versatile material with excellent properties, widely used in various industries such as automotive, household appliances, construction, electronics, footwear, packaging, helmets, sports equipment, and more. Polyurethane foaming agent is the most important additive in PU foam plastics, which directly affects the physical and mechanical properties, foam density, temperature resistance, and other aspects of PU foam. The foaming agents used to produce PU foam are usually divided into two types: chemical foaming agents and physical foaming agents. ## Chemical foaming agents Chemical foaming agents are gases produced by chemical reactions (water and isocyanate react to release CO₂) that make polyurethane foam. Examples are water, formic acid, higher organic acids (carboxylic acids), etc. ## Physical foaming agents Physical foaming agents are vaporized by the heat generated by the polyurethane polymerization reaction, making polyurethane foam. ## The evolution of foaming agents The first generation of foaming agents: low-boiling hydrocarbon compounds, mainly CFC-11, CFC-12, etc. In recent years, it has been found that these compounds are the culprit of destroying the earth’s ozone layer. After the fluorochlorocarbons enter the stratosphere, they are exposed to intense ultraviolet rays and release chlorine atoms, which cause the ozone layer to break and form ozone holes, endangering the survival of humans and other organisms. They were completely banned in 2010. The second generation of foaming agents: HCFCs (HCFC-141b difluorodichloroethane), with ideal thermal conductivity values, do not require major changes in production processes, and are widely used. However, they have high prices, and to achieve the same insulation effect as CFC-11, the foam density needs to be increased by about 10%; HCFCs have ODP values (ozone depletion potential), which still cause damage to the ozone layer. They are only a transitional foaming agent and will be gradually restricted to banned. The third generation of foaming agents: They are green foaming agents with performance close to CFC-11 and ODP (ozone depletion potential) of zero, such as HFCs, liquid CO₂, pentane series, etc. The pentane series includes cyclopentane, isopentane, and n-pentane (C5H12), which have an ODP (ozone depletion potential) value of zero, a low GWP (global warming potential) value, low toxicity, and little impact on the environment. At present, developed countries have fully applied the third-generation foaming agents. The domestic polyurethane industry started late, and small and medium-sized manufacturers of PU polyurethane composite panels are still using the second generation. Baoye Group’s Italian fully automatic composite panel production line in the Economic Development Zone of Deyang City, Sichuan Province uses the third-generation n-pentane series from Junyuan Petroleum Group, which is green and environmentally friendly, and contributes more to the realization of the country’s “carbon peak and carbon neutrality” dual carbon goals. ## N-pentane polyurethane foaming technology ### The characteristics of n-pentane Appearance and properties: colorless transparent liquid, with a faint aromatic odor. Melting point (℃): -129.8 Relative density (water=1): 0.63 Boiling point (℃): 36.1 Relative vapor density (air=1): 2.48 Critical temperature (℃): 196.4 Critical pressure (MPa): 3.37 Flash point (℃): -40 Explosion upper limit (%): 7.8 Ignition temperature (℃): 260 Explosion lower limit (%): 1.5 It is mainly used in the continuous production line of polyurethane panels, as polystyrene foaming and polyurethane foaming. ### The requirements of n-pentane for equipment 1. Because n-pentane is flammable, explosive, and volatile, it has special requirements for pumps and pipelines. For users with large production volume, it is recommended to use underground storage tanks. 2. During the production process, to prevent n-pentane leakage, ventilation should be paid attention to at all times, and n-pentane leakage sensors should be installed in the main positions. 3. The metering device should be installed in a separate ventilated room and equipped with a n-pentane leakage sensor. The pre-pressure and high-pressure of the pump should be equipped with detection devices. 4. The equipment should meet the requirements of producing high flame retardant (PIR) double-track of more than 30 meters. ### The advantages of n-pentane foaming technology 1. Compared with cyclopentane, n-pentane has better foam size stability. After the panel is formed, the shrinkage of the panel in the thickness and width directions is smaller than that of cyclopentane foam. 2. N-pentane foaming products have higher compressive strength in the thickness direction than cyclopentane and HCFC-141b foaming products. The compressive strength of PIRI can reach 182kPa. 3. Under almost the same foam core density, the feed density of the n-pentane foaming formula is lower. This means that the feed amount is reduced, the foam cost has a downward trend, and the compressive strength of the foam can reach the same or higher level. 4. Because HCFC-141b is highly polar and hydrophilic, n-pentane is weakly polar and oleophilic, and isocyanate is also oleophilic, n-pentane has better solubility with isocyanate, and the emulsification effect is better during high-pressure mixing in production. Therefore, the hard foam after n-pentane foaming has uniform and finer pores. 5. After a certain formula adjustment, the flame retardant performance of the n-pentane foaming product can reach or exceed the HCFC-141b foaming product. 6. The thermal insulation performance of the polyurethane rigid foam made by using n-pentane as a foaming agent can meet the thermal insulation performance requirements of cold storage panels. Foaming agents are related to the molding and insulation of polyurethane foam, which affects the product quality; they are also related to human protection of the atmosphere and the impact on climate change.

A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.

Blowing agents are additives used in the manufacture of foamed plastics, which have the advantage of lightness, contribute to material and cost savings, and are distinguished by the fact that they are thermally insulating. Blowing agents usually create fine and regular cellular structures during polymer processing.

Blowing agent plays a fundamental role in the production of polystyrene (PS), polyurethane (PU) and polyisocyanurate (PIR) insulations foam. A small quantity of blowing agent indirectly provides important performance characteristics to these foams as great thermal insulation properties.

The global warming potential (GWP) of the blowing agents used to manufacture insulation products like polyiso insulation can be an important consideration when assessing each product’s environmental impacts. Blowing agents function to increase the final thermal resistance or R-value of foam insulation, and also help to facilitate the manufacturing or foaming process.  

Manufacturers of laminated insulation products in North America use #pentane or #pentane #blends in their production processes. Pentane is a hydrocarbon with zero ozone depletion potential (ODP) and low-GWP. Manufacturers have utilized pentane technologies in product formulations for over 20 years.

Pentane has a GWP value of less than 10, which means that insulation products produced and sold in North America comply with climate regulations that limit the manufacture or installation of products produced with higher-GWP substances (including products manufactured with hydrofluorocarbons (HFCs) or blends thereof). Therefore, architects and contractors can continue to specify insulation products manufactured by PIMA members with confidence in both the industry’s performance and environmental scorecard.

Blowing agents can allow the polymer processor to achieve weight reduction and use less raw materials by introducing a finely controlled cell structure within the polymer. With the endothermic blowing agents, as part of their functionality, they will absorb heat energy from their surroundings.

Foam blowing agents encompass a wide variety of applications including refrigerators, buildings, automobiles, furniture, packaging, and many more. The blowing agent is used to create a cellular structure from liquid plastic resin, and in the case of foam used for insulation it functions as an insulating component of the foam.

When it comes to blowing agents, a controlled foam structure makes your production process go a lot smoother

Not only do blowing agents expand up to 60 times in volume, they also provide:

• highly controlled foaming
• closed, uniform cell structure
• guards against water penetration
• create internal pressure to combat shrinkage.

Blowing agent plays a fundamental role in the production of polystyrene (PS), polyurethane (PU) and polyisocyanurate (PIR) insulations foam. A small quantity of blowing agent indirectly provides important performance characteristics to these foams as great thermal insulation properties.

Blowing agents can allow the polymer processor to achieve weight reduction and use less raw materials by introducing a finely controlled cell structure within the polymer. With the endothermic blowing agents, as part of their functionality, they will absorb heat energy from their surroundings.

What is EPS

Polystyrene is one of the most widely used kinds of plastic. It is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene is a thermoplastic substance, it melts if heated and becomes solid again when cool.

Polystyrene is most commonly found in three forms. Rigid Polystyrene (PS), Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS).

Rigid polystyrene has many applications including disposable cutlery, cd cases, video/casette casings, components for plastic model toys as well as some margarine and yoghurt containers.  Extruded polystyrene foam has good insulating properties making it important as a non-structural construction material.  XPS is sold under the trademark Styrofoam by Dow Chemical, however this term is often used informally for other foamed polystyrene products.

How to produce foam?

Expandable Polystyrene / EPS:

This is PS Foam that uses Pentane gas (C5H12) as the blowing agent. During the material production process called “Polymerisation” the polystyrene resin granules impregnated with the blowing agent. EPS production processes begin in the pre-expansion process where the EPS bead will expand by the heat of steam usually 50 times in volume. The next step in the process is moulding process where expanded foam bead will be heated again with steam then they expand further until they fuse together, forming as foam products.

There are mainly 2 types of EPS moulding machines;

• Shape moulding machine that produce various shapes of foam products according to the molds such as icebox, helmet and packaging foam.
• Block moulding machine that produce block foam and sheet foam Expanded EPS foam bead contains 98% air per volume, only 2% is plastic. This make EPS foam very light weight, has low thermal conductivity because air is the best insulation, high compressive strength and excellent shock absorption. These properties make EPS to be ideal material for packaging and construction.

Polystyrene Paper (PSP):

This is a PS Foam which is produced by extruding process as another plastic. Production process start when put polystyrene resin pellets into the extruder that heated by electric. Foaming process occur at the end of extruder where the blowing agent, butane (C4H10) gas react with the melt plastic then become foam. The melted polystyrene foam is then extended as sheet then rolled as paper roll, that is why it is commonly known as “Polystyrene Paper”. The polystyrene foam sheet or polystyrene paper can be produced as many shape according to the mould by thermal forming process such as food tray, cups, bow, and food box.

There’s no any CFC’s in PS foam

Both EPS and PSP contain 95 -98 % air another 2-5% is polystyrene which is pure hydrocarbon. CFC’s is Chlorofluorocarbons which is totally different in its chemical structure from polystyrene. CFC’s has very low blowing point and uneasy to be maintained in EPS beads. Therefore, EPS Foam never use CFC’s at any stage of its production. The blowing agent used since EPS Foam was first introduced in 1952 by BASF  is Pentane gas which, does not contain any chlorine atoms as CFC’s. PSP Foam in the beginning used CFC’s as blowing agent. In the past two decades CFC’s are gradually phased out from plastics and refrigerator industries. PSP moulders in Thailand already use Butane (C4H10) as the blowing agent since the last 15 years. Butane gas is the gas that we use at home for cooking. The blowing agents that use in producing PS Foam are Pentane and Butane, which are pure hydrocarbon as polystyrene. They belong to the same chemical family, the paraffin series as methane, ethane, and propane gas.

How to manage the EPS foam waste

Apart from recycling by melting and compacting, there are many ways to manage the EPS waste as the followings:

• Crush in to small particle and mix with soil. Foam waste will improve ventilation in the soil, organic substances in the soil will become easier the humus.
• Mixing the crushed bead with cement to reduce the weight and increase insulation properties.
• Combustion at 1000 C with sufficient air supplies in to generate heat. Burning EPS require no any additional fuel, in fact EPS can replace the fuel normally required for combustion, l kg of EPS saves 1 kg = 1.2 – 1.4 Litre of fuel oil.

The Recycling of PS:

Since both EPS and PSP Foam are made of Polystyrene, which is thermoplastic, so that it will become again a polystyrene plastic when recycled. AMEPS members recycle both EPS and PSP Foam by first crushing into small particle then melting or compacting it. Melting can be done by heated roller, disk or screw extruders, where the regrind scraps is heated usually by electrical power for some time above the melting temperature. Compacting can be done by rotary compactors where pressure and frictional force create heat below melting temperature to soften the regrind scraps for only few seconds. This method also called “agglomeration”.PS pallet from recycled foam will be produced in various kinds of plastic products e.g. video and tape cassette and ruler. The other way to reuse EPS Foam is to mix the regrind beads with the new expanded bead for re-production in moulding process.