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Casting Polyurethane Prepolymer

What is Casting Polyurethane Prepolymer

 

Polyurethane prepolymers, also known as isocyanate terminated prepolymers, are polyols that have been reacted with diisocyanates but terminated with residual isocyanate groups. They are highly viscous resins synthesized by reacting a polyol such as polyether polyol or polyester polyol with a diisocyanate like MDI or TDI in a 1:1 or 1:2 stoichiometric ratio resulting in an isocyanate functional prepolymer. The resultant moiety from the isocyanate hydroxyl reaction is called a urethane linkage; isocyanate-amine reaction forms what are called a urea linkage. As more and more isocyanate groups in the prepolymer link up with hydroxyl or amine groups in the curative, many urethane linkages are formed and this is where the term polyurethane comes from.

Advantages of Casting Polyurethane Prepolymer

Wide range of hardness

The classification of hardness for polyurethane relies on the prepolymer's molecular structure and can be manufactured from 20 SHORE A to 85 SHORE D

Abrasion & impact resistance

For applications where severe wear prove challenging, polyurethanes are an ideal solution even at low temperatures.

 

Flexibility

Polyurethanes perform very well when used in high flex fatigue applications. Flexural properties can be isolated allowing for very good elongation and recovery properties.

 

 

High load bearing capacity

Polyurethane has a high load capacity in both tension and compression. Polyurethane may undergo a change in shape under a heavy load, but will return to its original shape once the load is removed with little compression set in the material when designed properly for a given application.

 
Why Choose Us
 
01/

Our Factory
Zibo Hengjiu PU Technology Co., Ltd. is a professional manufacturer which engaged in the R & D, production and sales of polyurethane prepolymer, polyester polyol and polyurethane elastomer finished products.

02/

Advanced Equipment
The company has the most advanced production and testing equipment in China, has an annual production capacity of 30000 tons of various casting polyurethane prepolymers, polyester polyol and polyurethane elastomer finished products realizes the chain production from upstream raw materials to downstream products.

03/

Production Market
The company's products not only spread all over the national market, but also exported to Canada, Australia, India, Turkey, Russia, Indonesia, South Korea, Malaysia and other international markets.

04/

One-stop Solution
The company has a group of high-quality technical talents, which can provide customers with comprehensive services such as pre-sales, in-sales, after-sales and technical guidance.

How Does The Shrinkage Rate Of Casting Polyurethane Prepolymer Change
 

●With the extension of the curing time, it changes in a zigzag shape;

 

●Polyurethane prepolymer will decrease with the increase of environmental temperature; It will fluctuate with the increase of environmental humidity.

 

●Polyurethane prepolymer will increase with the increase of mold temperature. Different mold structures have different resistance to shrinkage, with the smallest longitudinal direction and the largest transverse direction.

 

●Before a certain length, the shrinkage rate increases with the increase of the flow path length, but after a certain length, the shrinkage rate decreases with the increase of the flow length.

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Precautions For The Use Of Casting Polyurethane Prepolymer

 

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Polyurethane prepolymer is a kind of polyurethane prepolymer based on TDI and polyether polyol. It has the characteristics of high elasticity, good abrasion resistance, low endogenous heat, and hydrolysis resistance. It has the advantages of dynamic performance requirements. obvious advantage. Products made with it have good performance in terms of resilience, low temperature properties and toughness. Moreover, it also has lower operating viscosity and longer reaction time. It has good operability when manufacturing products, is not sensitive to water vapor, short demoulding time, high yield, wide maturation conditions, etc. In addition to providing better physical properties and convenient operation, it also has an outstanding performance in ensuring environmental safety, health and hygiene.

 

Pay attention to sealing during use. If it cannot be used up all at once, the polyurethane prepolymer after use should be sealed and stored under nitrogen protection. At low temperatures, the prepolymer will condense into a viscous liquid filled with lard. It is not suitable to use electric heating rods, electric ovens and other equipment when heating the prepolymer, because the heating method is too concentrated and will cause local material degradation. Therefore, it is generally appropriate to heat the prepolymer at 70℃ to 80℃. Do not use the prepolymer before it has melted. The uneven mixing of prepolymer and curing agent will cause partial color difference in the product.

Method Of Eliminating Air Bubbles By Polyurethane Prepolymer
 

Use zeolite molecular sieve to defoam

The critical diameters of water molecules are 0, 27-0, 32nm, the molecular lengths are 0, 32nm, the critical diameters of CO2 molecules are 0, 28nm, and the molecular lengths are 0, 41nm. In the synthesis of prepolymer adhesives (using PTMG and TDI). At 10℃, relative humidity 40%, and molecular sieve content up to 3%, no bubbles appear in the synthetic prepolymer adhesive.

 

In the defoaming of prepolymer adhesives, 13X activated zeolite molecular sieve is often used, and its activation temperature is 200-350℃. 13X molecular sieve can eliminate the trace moisture in the polyurethane adhesive, and can also absorb the carbon dioxide produced by the reaction of polyisocyanate and water.

Solvent defoaming method

When synthesizing the prepolymer adhesive, generally use ethyl acetate or acetone as the solvent when using polyester polyol, and use toluene as the solvent when using polytetracyanofuran. After adding the solvent, let it stand for a period of time before defoaming. When using solvent defoaming, the surface tension of the solvent has a great influence on the elimination of bubbles. The surface tension is small (under 35×10-3N/m), the bubbles are easy to eliminate, and the surface is not easy to foam. When choosing a solvent, pay attention to the influence of the solvent on the reaction. The greater the polarity of the solvent, the easier it is to form a hydrogen bond association with the -OH group, thereby reducing the reactivity of the -NCO group and the -OH group.

 
Why Is The Cup Test Required For The Production Of Casting Polyurethane Prepolymer Products
Observe the ratio of A and B materials

When the ratio of A and B materials is out of balance, the tear strength of free foam materials is particularly easy to observe. At this time, increase or decrease a little A, B material and then carry out the cup test, and so on, until the center of the ratio of the two is found. But sometimes it will be difficult to find the matching center. It may be caused by uneven mixing, leakage of methylene chloride (cleaning fluid), overheating and overcooling of the ambient temperature. At this time, separately test the respective flow rates of A and B materials to determine whether the flow ratio of A and B materials is normal. It should be noted that if the raw material is prevented for too long, the central value of the ratio of the polyurethane prepolymer is not the value of the standard ratio. In many cases, the amount of B material will increase, and the proportioning center needs to be searched again.

Detection of foaming density

Whether the free foaming density is consistent with the standard free foaming density is an important indicator to observe whether the reaction reactivity of the stock solution is normal. Too high or too low indicates that the reaction is not proceeding normally, and the gel and foaming speed are not in harmony . The difference between the free foam density and the density of the finished product cannot be too small, otherwise, if the foaming pressure is too small, the surface quality of the finished product will deteriorate. In actual production, because the foaming pressure is too small, the surface quality of the finished product will deteriorate. In actual production of polyurethane prepolymer, insufficient printing foaming pressure causes problems. For example, the commonly used PU sole stock solution generally has a free foaming density standard of about 0.25kg/cm3. The density of the finished product is 0.5~0.7g/cm3, and the difference is more than 0.25kg/cm3. If the density of the finished product is reduced to about 0.4g/cm3 in order to save materials, resulting in the difference between the two being below 0.15g/cm3, the surface quality of the PU sole at the production site will be poor.

Check the lotus leaf for bubbles

Sometimes, when the mixture of material A and B is poured dry, air bubbles have been brought into it. This may be caused by the imperfect sealing of the machine head and imperfect sealing of the sprayed polyurethane prepolymer. Therefore, it can be observed by self-foaming. When the new mixing head is just replaced, bubbles are prone to appear in the first few cups, but after a few more cups of experimentation. Since the source of the leak has been sealed by the mixed liquid, the situation will get better.

Detect the phased indicators in the automatic foaming process

The reactivity index of the automatic foam test, in addition to the strength index, there are milky white time, rise time, non-stick time, and elastic time. Check these time values.

Applications of Casting Polyurethane Prepolymers

 

 

Coatings

Prepolymers are used as binders, crosslinkers and intermediates in manufacturing coatings for wood, concrete, leather and various industrial applications. Their excellent adhesion, chemical resistance and flexibility makes them ideal for coatings.

 

Adhesives and Sealants

The film forming and adhesive properties of prepolymers are leveraged to produce structural and high-performance adhesives as well as sealants for construction and automotive applications.

 

Elastomers

Prepolymers impart flexibility, elasticity and high strength to elastomers used in hoses, gaskets, rollers and various flexible molded articles. They aid in processability and enhance mechanical properties.

 

Footwear

The mechanical strength and flexibility imparted by prepolymers in polyurethane enables their use in manufacturing shoe soles, heels and sport shoe midsoles providing comfort and durability.

 

Foams

Prepolymers play a crucial role in production of flexible and rigid polyurethane foams as cushioning and insulation materials in bedding, furniture, packaging, construction and automotive industries.

Types Of Casting Polyurethane Prepolymers
 

Based on the polyol/diisocyanate ratio and reactants used, prepolymers can be categorized as:

MDI Based

Formed from reaction of MDI with polyester polyols or polyether polyols. Offer high strength, hardness and chemical resistance. Widely used.

 

 

TDI Based

React TDI with polyols. Provide flexibility and high elongation. Used in elastomers, sealants and adhesives.

 

Polyester Based

Have good hydrolytic stability and strength. Used in coatings.

 

 

Polyether Based

Impart flexibility and low temperature impact resistance. Used in cushioning foams and coatings.

 
Manufacturing Process of Casting Polyurethane Prepolymers
 

Reaction of Polyol and Diisocyanate

Polyether polyol or polyester polyol is charged into the reactor and heated to the required temperature. Diisocyanate like MDI or TDI is added slowly with agitation.

 

Controlled Polyaddition Reaction

The exothermic polyaddition reaction between hydroxyl groups of polyol and isocyanate groups proceeds. Process parameters like temperature, catalysts are controlled.

 

Termination Reaction

Once the pre-set NCO index is reached, the prepolymer is terminated by residual isocyanate groups and deactivated by adding catalyst kill.

 

Filtration and Packaging

The viscous prepolymer solution is filtered to remove impurities and filled in drums, IBCs or bulk tankers.

 

Quality Testing

Routine testing of properties like NCO content, viscosity, functionality etc is done to ensure product quality meets specifications.

 
Advantages of Polyurethane Prepolymer When Compared to Conventional Materials

 

vs. Rubber vs. Metal vs. Plastic
High abrasion resistance Lightweight High impact resistance
High cut & tear resistance Noise reduction Elastic memory
Superior load bearing Abrasion resistance Abrasion resistance
Thick section molding Less expensive fabrication Noise reduction
Colorability Corrosion resistance Variable coefficient of friction
Oil resistance Resilience Resilience
Ozone resistance Impact resistance Thick section molding
Radiation resistance Flexibility Lower cost tooling
Broader hardness range Easily moldable Low temperature resistance
Castable nature Non-conductive Cold flow resistance
Low pressure tooling Non-sparking Radiation resistance

 

Outlook for Casting Polyurethane Prepolymers Market

 

The global polyurethane prepolymers market is forecast to grow at over 5% CAGR through increasing usage in coatings, adhesives, sealants, thermoplastic polyurethanes and various consumer and industrial applications. Rapid growth of key end use industries like footwear, construction, automotive, packaging and furniture will boost demand.


Continuous product innovation to develop new grades catering to changing industry and regulatory trends along with expansion into emerging markets in Asia Pacific and Middle East regions are factors expected to fuel the prepolymer market in the coming years. However, volatility in raw material prices remain a key challenge. Overall, polyurethane prepolymers market outlook looks positive owing to their excellent performance attributes and versatile usage profile.

FAQ

Q: How to make a polyurethane prepolymer?

A: Polyurethane prepolymer which can be converted into a final product by reaction with a curative or chain extending agent is made by reacting polyisocyanate with polyol in the presence of an amount of an aliphatic hydrocarbon which is a solvent for the polyisocyanate but a non-solvent for the prepolymer.

Q: What is polyurethane chemical used for?

A: Polyurethane, mostly in the form of flexible foam, is one of the most popular materials used in home furnishings such as furniture, bedding and carpet underlay. As a cushioning material for upholstered furniture, flexible polyurethane foam works to make furniture more durable, comfortable and supportive.

Q: What is polyurethane prepolymer used for?

A: Polyurethane prepolymer products are used as precursor materials for a variety of applications including molding compounds, sealants and adhesives, coatings, and other specialty products.

Q: What is the difference between a monomer and a prepolymer?

A: In polymer chemistry, the term prepolymer or pre-polymer, refers to a monomer or system of monomers that have been reacted to an intermediate-molecular mass state. This material is capable of further polymerization by reactive groups to a fully cured, high-molecular-mass state.

Q: Is polyurethane the same as polymer?

A: Polyurethane refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from a wide range of starting materials.

Q: Is polyurethane a synthetic polymer?

A: Polyurethane, any of a class of synthetic resinous, fibrous, or elastomeric compounds belonging to the family of organic polymers made by the reaction of diisocyanates (organic compounds containing two functional groups of structure ―NCO) with other difunctional compounds such as glycols.

Q: How to prepare polyurethane?

A: Polyurethanes are prepared by reacting polyols (alcohols with more than two reactive hydroxyl groups in each molecule) with diisocyanates or polymeric isocyanates. Suitable catalysts and additives are used wherever necessary.

Q: What is the difference between polyurethane and urethane?

A: Because "poly" means "many," polyurethanes are essentially full of many urethane compounds/groups. Urethane, on the other hand, is its own chemical group. It can be either rigid or soft, giving it a range of different uses that polyurethane is not suited for.

Q: Is polyurethane rubber or plastic?

A: Polyurethane (PU) is a unique polymer that is elastic like a rubber but can be repeatedly stretched and reformed like a plastic. This tough, flexible and hard wearing material can be formulated using a wide range of starting materials to develop everything from paint to car parts, shoe soles and seals.

Q: What is isocyanate prepolymer?

A: What Does Isocyanate Prepolymer Mean? An isocyanate prepolymer is a type of polyurethane prepolymer in which all of the polyol hydroxyl end groups have reacted with isocyanate groups. The end result is a compound with isocyanate functionality at the termini instead of hydroxyls.

Q: What is the difference between prepolymer and oligomer?

A: The key difference between prepolymer and oligomer is that a prepolymer is an intermediate of a polymerization reaction, whereas an oligomer is a polymer material composed of comparatively a few monomer units. Therefore, a prepolymer is an intermediate compound, while an oligomer is a final product.

Q: Which is better, polyurethane or polymer?

A: PU sealants have a higher yield and tensile strength and are suitable for applications where the pH value is not very high or low. But MSP has a clear advantage in terms of bonding and resistance to chemicals, cold and heat.

Q: How is polyurethane made?

A: Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule) with a diisocyanate or a polymeric isocyanate in the presence of suitable catalysts and additives.

Q: What is the raw material for polyurethane?

A: Polyurethane foams are produced by reacting polyols and diisocyanates, both products often derived from crude oil. The main diisocynate used in the production of flexible polyurethane foam is TDI (Toluene diisocyanate).

Q: Is polyurethane hard or soft?

A: Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers. One reason why urethane is amazing is it varies widely in durometers. Polyurethane can be cast as soft as a 20 Shore A (ex.: rubber band) up to a 90 Shore D (ex.: nylon, military combat helmet).

Q: Is polyurethane rubber or latex?

A: Rubber and Polyurethane are as different as they are similar: Both rubber and polyurethane have elastic qualities, are mouldable and flexible. Rubber materials generally offer better grip qualities whereas polyurethanes are generally seen as more durable.

Q: Which isocyanate is used for polyurethane?

A: The most commonly used isocyanates for polyurethane production are the aromatic diisocyanates toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI) which form the basis for >90% of all polyurethanes .

Q: Is polyurethane a synthetic material?

A: Polyurethane fibre is defined as a synthetic fibre in which the fibre-forming substance is a long-chain synthetic polymer comprised of at least 85% segmented polyurethane.

Q: What is the chemical composition of polyurethane?

A: The chemical formula is C27H36N2O10“. Polyurethane is another synthetic resin-type varnish. Polyurethane foam is formulated in different ways for different uses. Urethane is a carbonyl-containing functional group in which the carbonyl carbon is bonded to both an -OR group and an -NR2 group.

As one of the leading casting polyurethane prepolymer manufacturers in China, we warmly welcome you to buy high-grade casting polyurethane prepolymer made in China here from our factory. All our products are with high quality and competitive price. For more information, contact us now.

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