In the field of safety glass and ballistic structures, understanding certain phenomena is essential to ensure reliable performance. Among the factors that can seriously compromise system integrity, the role of plasticizers present in some interlayer films is particularly critical, as their interaction with the structural assembly is the primary cause of numerous premature failures.

Interlayer Film Properties in BRG Layer Bonding

Interlayer films that bond the different layers of BRG (Bullet Resistant Glass) blocks must exhibit high optical transparency, robust and with adhesive properties, and suitable mechanical characteristics to function effectively as energy-disippating and distributing elements during impacts. Their performance is critical to the functionality, resistance, and durability of BRG structures.

Mainly, interlayer films must primarily consist of flexible and elastic materials, as this is the only way to provide the necessary mechanical properties for an essential performance by managing impact stresses. Elasticity refers to a material’s ability to deform under load and subsequently recover its original shape without permanent damage.

Misuse of Rigid Films

In some cases, overly rigid or hard films are employed under the mistaken assumption that increased rigidity enhances system performance. However, excessive rigidity limits the film’s capacity to absorb stresses, accomodate movements, and distribute projectile tensions with high kinetic energy, thereby, impairing overall performance. Consequently, excessively rigid films require mixture or reformulation with other materials to enhance elasticity and achieve appropriate mechanical behaviour.

Use of Plasticizers in Interlayer Materials

PVB is the traditional interlayer film used in laminated glass, and in its natural state at room temperature, it is a rigid material. To transform it into a flexible and procesable sheet during lamination, molecules known as plasticizers are incorporated. These act as an “internal lubricant” that provides viscosity, flexibility, and ease of adhesión between glass layers and other materials within a single manufacturing process.

Up to this point, it seems like a perfect solution – but time and temperature tell another story.

Plasticizers are, in fact, molecules distinct from those of the base polymer. Although they mix with it, they are not completely immobilized. Over time, they move and shift randomly within the polymer matrix. These molecular displacements are unavoidable and become more pronounced as the temperature of BRG structures increases. The higher the temperature, the greater the molecular mobility, which accelerates the internal migration of the plasticizers and progressively alters the material’s properties.

Plasticizer Migration: A Progressive Issue with Serious Consequences

Over the years, the plasticizers present in PVB tend to slowly move within the polymer matrix itself or even migrate toward adjacent layers of the BRG block, such as PC (polycarbonate) or TPU (thermoplastic of polyurethane). They may also escape through the laminate edges, particularly in warm climates or under intense solar exposure.

As a result, plasticized PVB loses its internal balance – it becomes stiffer, less adhesive, and les capable of distributing impact energy. That is to say, it loses elasticity through time.

Degradation Induced by Plasticizer Migration in PVB-Based Ballistic Laminates

Hardening of the interlayer film, reducing its ability to absorb and dissipate energy.

Loss of adhesion, especially along the edges, where delamination typically begins.

Chemical risks for PC, which may develope cracks due to embrittlement or chemical attack by the plasticizer.

Accumulation of dust and contaminants on the PC surface, as exuded plasticizer makes the laminate surface tacky, attracting dirt and debris.

PC coating delamination, since the plasticizer can soften the interface and lead to detachment of the “anti-spall” layer.

Optical alterations, as plasticizer migration causes micro-heterogeneities and local changes in refractive index, resulting in haze, turbidity, and los of optical transparency and clarity.

Reduction of acoustic damping, due to the decreased ability of the interlayer to dissipate sound vibrations

In practical terms, laminated systems using plasticized PVB generally exhibit visible degradation or structural integrity loss after approximately 3 years, depending on environmental conditions such as temperature, humidity, and solar exposure.

• Hardening of the interlayer film, reducing its ability to absorb and dissipate energy.

• Loss of adhesion, especially along the edges, where delamination typically begins.

• Chemical risks for PC, which may develope cracks due to embrittlement or chemical attack by the plasticizer.
• Accumulation of dust and contaminants on the PC surface, as exuded plasticizer makes the laminate surface tacky, attracting dirt and debris.
• PC coating delamination, since the plasticizer can soften the interface and lead to detachment of the “anti-spall” layer.
• Optical alterations, as plasticizer migration causes micro-heterogeneities and local changes in refractive index, resulting in haze, turbidity, and los of optical transparency and clarity.
• Reduction of acoustic damping, due to the decreased ability of the interlayer to dissipate sound vibrations

Plasticizer-Free Interlayer Films: Formulated TPUs

A modern technical solution that has emerged as a direct alternative to traditional PVB is the use of formulated TPU (thermoplastic polyurethane). Unlike PVB – which requires external plasticizers to achieve flexibility – TPU incorporates its viscoelastic component within its own molecular chain, eliminating the need for added plasticizers.

Thanks to this inherently stable structure, TPU maintains its flexibility and transparency over time, completely avoiding issues related to plasticizer migration and providing more consistent adhesión to both PC and glass.

For these reasons, TPU has become the most advanced and reliable solution for laminated systems in BRG (Ballistic Resistant Glass) constructions designed for long service life, progressively replacing PVB in applications where long-term stability is critical.

In Summary

From Traditional PVB to Next-Generation TPU : Rethinking Interlayer Performance

PVB is widely used because it was the first interlayer film developed for architectural laminated glass and was later adopted for ballistic glazing structures. However, its inherently rigid nature makes it dependent on plasticizers – not only for the manufacturing process but also to achieve the mechanical, optical, and adhesive properties required to function effectively as an interlayer.

These plasticizers may seem like an initial ally, but over time they become the source of cracking, haze, loss of adhesion, and delamination. Replacing them with intrinsically flexible materials, such as TPU, represents not only a technical improvement but also a significant advancement in durability, optical stability, and ballistic performance.

Therefore…

If your current ballistic structures use PVB, it is highly likely that the plasticizer it contains has already started the countdown on your glass system’s service life.

The root cause of many cases of delamination, haze, or PC cracking is rarely found in the glass itself or in the ballistic design – it lies in the chemistry of the plasticizer and its inevitable migration out of the film.

If you are currently:

Redesigning a BRG package to extend its service life

Facing warranty claims for delamination or optical defects after just a few years

Evaluating advanced materials for high-value applications (armored vehicles, high-security architecture, ATMs, Access control systems…)

• • Redesigning a BRG package to extend its service life
  • Facing warranty claims for delamination or optical defects after just a few years
  • Evaluating advanced materials for high-value applications (armored vehicles, high-security architecture, ATMs, Access control systems…)

Then it is worth comparing, with real-world data, the performance of plasticized films (PVB) versus formulated, plasticizer-free TPU solutions.

We can help you to:

Assess the risk of premature failure in your current designs.

Propose BRG configurations based on TPU with high transparency, optical stability, and superior durability.

Develop pilot tests and validation programs, aligned with your geometries, protection levels, and regulatory requirements.