NETMELT is Concentrol’s range of hotmelt adhesives used for gluing different substrates, porous or non-porous, such as: paper, cardboard, wood, cork, plastic, fabrics, etc.

They are presented in pellets, blocks or pillows, depending on the reference.

Due to their versatility, they can be used efficiently in a wide range of sectors: Food, Graphic Arts, Cases/Packaging, Electronics, Wood, Textile, Automotive, etc.

The use of this type of adhesive offers the consumer the possibility of high work rates and excellent performance. Concentrol also offers custom formulated products to meet your specific needs.

Most references comply with FDA standard 175.105.



NETMELT PUR hotmelt adhesives are thermoplastic polyurethane (PU) prepolymers with a 100% solids content, so they do not contain solvents. They are also called structural, chemically hardening or curable adhesives, as they require a chemical reaction. In this case, polymerization caused by water from ambient humidity, which acts as a chain extender. This reaction is what produces the final adhesion force between two surfaces, in which the polyurethane hotmelt has been used for their union.

When the prepolymer reacts with the ambient humidity or that of the substrate itself, this prepolymer increases its molecular weight due to the crosslinking of the chains during polymerization. A final thermosetting adhesive product is obtained, which does not melt. Therefore, once fully cured, they usually have good resistance to temperature and chemical products.

PUR Hotmelts are solid products at room temperature, chemically terminated in reactive isocyanate groups (-N=C=O), synthesized, like all polyurethanes, from polyester or polyether polyols or their mixtures, with polyisocyanates. Due to safety requirements, the resulting prepolymers must be very low in free isocyanates, which is the fraction that remains unreacted at the end of the prepolymerization process. Monomeric isocyanates are toxic. Even at low concentrations, they can damage the respiratory organs, eyes, and skin, and can cause allergic sensitization, among other effects.

Our range of NETMELT PUR melts by the action of heat and remains in the form of a more or less fluid liquid. In this state, they are applied to a wide variety of substrates. When they cool down, they solidify, generating an initial strength very similar to that of a conventional non-reactive hot melt adhesive. It then becomes, after chain extension with ambient humidity, an excellent bond strength on supports where traditional HM, EVA-based or polyolefin, are completely ineffective.


Differences between PUR hot melt adhesive and conventional EVA or Polyolefin based

Although both products are applied in the same way using melting equipment:

  • the hot melt adhesive is heated until it is in liquid form,
  • is applied to the materials to be joined,
  • these materials are put in contact where the adhesive has previously been deposited,
  • cools while the glue joint is pressed, they are different, although with some similar properties.

Next, characteristic aspects of the conventional adhesive and the reactive adhesive are compared:

Conventional hotmelt Reactive hotmelt
Application temperature >150ºC 90 – 140ºC → lower energy costs 
Reactivity None With humidity → final bond strength may take time
Thermal resistance Limited because it always maintains its melting point, the environmental heat can affect the glue. Excellent (does not melt)
Adhesion to substrates Good but more limited Wide variety of materials
Cost Not very high High, but less is needed. Ambient heat can affect bonding
(VOC) Volatile Organic Compounds Yes Yes
General aspects Limitation according to substrates, hot melt always. Cheaper price. Wide range of materials, thermosetting bond after curing.


Outstanding properties of NETMELT PUR reactive polyurethane hotmelt adhesives

  • 100% solids, do not contain solvents.
  • It offers a highly versatile chemistry, since it can be adjusted among others: viscosity, chemical affinity, open time, hardness, flexibility, initial adhesion, final adhesion, etc.
  • Applicable on a wide range of substrates (very varied properties for very specific applications). Graphic arts, Cases/Packaging, Electronics, Wood, Textile, Automotive, etc.
  • It allows the joining of a wide variety of products that are normally difficult to join, including non-porous materials, plastics, and metals.
  • Achieves a high-quality bond with materials that are different from each other.
  • Excellent properties at high and low temperatures.
  • Good resistance to chemicals once fully cured.
  • Effective for indoor and outdoor applications.



Hotmelt PURs are made by reacting polyol blends with excess diisocyanate. The reaction of the alcohol group (-OH) with the isocyanate group (-NCO) produces an urethane group, as can be seen in the following figure.

The prepolymer obtained is packaged hot and sealed under an inert and vacuum atmosphere, to avoid any contact with ambient humidity.

Containing an excess of diisocyanate, the product cannot fully react to polyurethane and remains a hot-melt product. In contrast, fully polymerized polyurethanes (after application and curing) are solid products and are classified as plastics.

When formulating an HMPUR, the choice of components is important and governs the final properties. Each of the raw materials can be adjusted appropriately to obtain the required shelf life, open time, and early and late strengths.

The main properties are obtained with the use of a variety of properly formulated polyols, isocyanates and additives. Polyols are used to vary the open time, the setting time or initial adhesion, the viscosity and the ability to wet uniformly on the support.

Typical polyols used are polyesters, which can be crystalline or amorphous; and polyethers based on ethylene and propylene oxides; although the latter are less used in the adhesive sector. One or another type of polyol (polyether or polyester) or mixtures of these is chosen to generate final effects and properties of the material to be formulated.

Below is a table with these characteristics: 

Properties Influence of polyester Influence of polyether
Hydrolysis resistance +
Resistance to microorganisms +
Solvent resistance +
R-UV resistance +
Behavior at low temperatures +
Behavior at high temperatures +
Easy processed +
Resilience +

The most widely used polyisocyanate for the manufacture of HMPUR is diphenylmethane diisocyanate, commonly abbreviated MDI. It exists in three different isomeric forms, 2,2′-MDI, 2,4′-MDI and 4,4′-MDI, the latter being, however, the most used and qualified as “pure MDI” or simply MDI. Commercially, we do not find the pure product, mixtures of two isomers or even modified (liquid and polymeric).

Additives can be added to these formulations to modify and improve certain properties. These can be catalysts or hardeners to accelerate curing, moisture scavengers to extend shelf life, thickeners and thixotropic agents to modify viscosity, or fillers to adjust physical properties, plasticizers, tackifying agents, flame retardants, UV markers, antioxidants. , UV stabilizers and pigments, among others.


Polymerization mechanism – curing 

Once the HMPUR is applied and cooled to solidity, the curing reaction with ambient moisture begins. Absorption of water from the atmosphere results in the formation of carbamic acid which, being unstable, decomposes, forms an amine, and releases carbon dioxide (CO₂) as a gas. This amine can react with a free isocyanate group, and in turn form an urea group.

The reaction ends when all the available isocyanate groups are consumed, obtaining a very stable compound.

One consequence of the polymerization reaction is that the urethane prepolymer, which was initially linear, crosslinks in a three-dimensional fashion due to crosslinking of the polymer chains. In addition, due to these reactions, the polymer increases considerably in weight during curing, improving the adhesion force. Therefore, if the adhesive is formulated correctly for a specific application, it will show a clear increase in final resistance; more or less flexibility, both at low and high temperatures; and great resistance to hydrolysis, heat, and solvents.

Although there are many advantages to moisture curing hot melt adhesives, the moisture content of the substrates must be high enough to achieve complete polymerization.

Sometimes the humidity is high enough in the environment, but low in the support. This makes it difficult for moisture to penetrate the system, due to the difference in reaction speed of the surface facing the outside and the one facing the inside. An outer layer of polymerized PU is formed that does not allow water vapor to enter, and, therefore, there are areas without the completed reaction with less adhesion force.

As discussed above, carbon dioxide bubbles form, which can also undermine the bond strength of the adhesive. More frequent if the adhesive layer is too thick.

The polymerization – curing time depends on:

  • The amount of adhesive applied. A thin layer cures faster.
  • Environmental conditions: humid environments favor faster curing.
  • Type of substrate: the more porous it is, the better anchorage and the shorter the curing time.
  • The use of catalysts or hardeners greatly accelerates curing.

In the figure above you can see the two stages by which the HMPUR system achieves the bond strength, the first stage by a physical mechanism (solidification) and the second stage by a chemical mechanism (polymerization). (a) indicates the initial resistance, (b) refers to the open time and (c) indicates the setting time. 


Application sectors

The main application sectors are:

Binding. The advantages of binding with PUR glue is that it can be done on practically any type of paper, hard cover or soft cover, resists extreme temperatures, and offers greater flexibility and adhesion than other traditional glues, which offer a less malleable product. This method offers books of greater durability and quality at the lowest possible manufacturing cost and without being sewn.

Automotive. Although different car manufacturers have different adhesion requirements, the basic content is the same and the demand from the car market also points in the direction of using PUR hot melt adhesives. Fast, efficient, high-performance adhesives are needed to match application techniques and meet the demanding requirements of modern vehicle assembly. They are used in the union of different substrates: plastics such as ABS, PC…; metal, textile and wood; for dashboards, armrests, floors, ceiling, seats, door panels, gutters, carpets, upholstery, interior trim, etc.

Joinery, carpentry and furniture making. PUR adhesives are an excellent choice for carpentry and other wood applications. They provide the high strength needed to hold materials together and eliminate the need for screws and nails to assemble wood furniture. This includes surface laminating, furniture edging and profile cladding.

Casing. The use of HMPUR is especially recommended for packaging to show content and totally transparent plastic cases (PET, PVC, PP, PE…), as well as hybrids, for creating a union with excellent resistance and great transparency, avoiding the formation of bubbles inside the joint and thus improving its visual appearance.

It is also used in the electronics, textile, construction and food sectors.



The main references currently available and the different sectors of application are shown.

Binding  NETMELT PUR EN-2231 CER HV 




Automotive NETMELT PUR MP-2270 C 






Textile  NETMELT PUR PT-2216 C 





Casing (PP, PVC, PET…)  NETMELT PUR PP-2210 M


Cosmetic NETMELT PUR PP-2260 C 
Cork (food industry)  NETMELT PUR FS-2045 C NETMELT PUR FS-3016 C