Lonza's P-25 offers more controlled polyurea curing

by Marc Broekaert consultant; Gaetano La Delfa; Stefan Ellinger and Maria Luisa Longo, Lonza

Lonza has worked to develop a new, slower curing additive for the polyurea market, which is designed to offer a longer working time for polyurea and polyurethane applications and enable the use of low-pressure machinery in this sector.

Introduction

Designated Lonzacure P-25 Liquid, the product is an aromatic di-amine chain extender. It is designed to be easy-to-handle in two-component polyurethane cast and polyurea spray applications.

It is suitable for use in formulations where extremely high thermo-mechanical, chemical- and abrasion-resistance are key requirements.

The curative has a low level of toxicity, which lowers worker risk in industrial settings with routine exposure controls.

The new material is one of a number of Lonzacure products for polyurethane/polyurea applications.

Lonzacure P-25 liquid has controlled reactivity because it incorporates a carefully selected side group and the molecule is sterically hindered.

This chemical structure helps formulators control the cure rate on high-speed spray machines and low-pressure spray applications. It is also designed to improve the film properties of room temperature castable systems.

The material offers opportunities for applicators to use it in systems on low-pressure machines with a modified gun mixing unit.

This could be beneficial for applicators because the capital cost of low pressure machines is generally lower than high-pressure machines.

This proprietary molecule is liquid at typical processing conditions, is non-mutagenic, giving a negative result to the Ames test.

The grade has density of 1.15 kg/m3 and equivalent weight of 113 g/eq. It is odourless and dark brown in colour. The product has been registered with the American Chemical Society and has the following CAS number: 1616795-05-1.

Experimental

We have tested the additive in a number of real-life simulations and experimental spraying and testing were carried out at Huntsman’s research centre in Everberg, Belgium A Graco XP-II machine with an airpurge gun and flat spray nozzle was used in this process.

This was fitted with a low-output mixing chamber AF2020 and adapted with two small tanks to reduce the quantity of Lonzacure P-25 liquid needed for trials The temperature of the two components, and heated hoses was 80°C, and mix pressure ranged from 185 to 190 bar.

Table 1 shows a typical series of formulations for a standard polyurea system. Key physical properties of these materials are shown in Table 2.

Results

The P-25 Liquid material offers significantly slower reactivity than the standard DETDA 80 formulation and gives good surface quality and reduced overspray problems that can occur with standard DETDA80 systems.

Table 2 shows that the material made with Lonzacure-P25 has comparable hardness to the DETDA80 formulation. There are significant improvements in tensile, elongation at break and angle tear properties for formulations based on P-25 Liquid compared with a standard toughened DETDA80 coating formulation.

After samples were sprayed, a number of accelerated tests were carried out after 1 hour post-cure at 60˚C. The aim was to give an indication of the length of post cure that would be needed for the reaction to reach completion.

Typically, polyurea is post cured for a considerably longer period of time – sometimes more than a week .

Following the accelerated post cure, infrared spectroscopy of the P-25 system shows a small peak for isocyanate at 2277cm-1.

Quartz UV (QUV) testing showed that colour change after 500 hours is less in formulations with the P-25 Liquid than with other aromatic systems based on a 1:1 mixture of P-25 and DETDA80. This is despite the Lonzacure P-25 formulation being darker brown than the formulation based on P-25:DETDA80.

The material was also trialled in hard sprayable polyurethane systems. Such formulations are shown in Table 3 and their properties are shown in Table 4.

Table 3 shows that Lonzacure P-25 is more reactive than the presently used slow chain extenders.

It also shows that the fully-cured material can achieve a high hardness and have limited flexibility. Tensile and shear strength indicate that the materials have good mechanical properties.

It was not possible to reduce the stress build up during the first phase of the curing process.

Once again we carried out an accelerated test , and once again, infrared spectroscopy showed a small peak for isocyanates but after 1 hour of post cure at 60C an additional urea formation spike at 1640 cm-1 is observed. Again, in real life situations, a longer post cure process at room temperature would be used.

Summary

In summary, in a formulation for a hard, spray able polyurea system P-25 helps to produce polyurea systems with significant higher temperature resistance than existing slow chain extenders.

Although still classified as a slow curative, Lonzacure P-25 provides a faster curing system with enhanced properties combining high tensile strength with a high flexibility and superior wear resistance compared to a conventional DMTDA systems. There is the possibility of fine-tuning formulations to optimise properties, for example, it is possible to produce high-hardness polyurea formulations without adding abrasive fillers.

The product gives controlled reactivity with excellent film properties.

And the material’s reactivity profile opens the way for its use on low-pressure machinery.

Acknowledgements

We would like to thank Servaas Holvoet and Stijn Roekaerts at Huntsman for their support with the preparation, spraying and testing of the materials.

Gaetano La Delfa, Lab Manager, Global Marketing Coating & Composite Materials, Lonza, Lonzastrasse CH - 3930 Visp, Switzerland Tel: +41 27 948 6973 mailto: [email protected] Maria Luisa Longo, Global Marketing Manager, Coating & Composite Materials, Lonza, 90 Boroline Rd, US - 07401 Allendale Tel: +1 201 683 2992 mob : +1 408 594 9353 mailto: [email protected] www.lonza.com