A transparent evolution

Ever since a French chemist knocked over a bottle of cellulose acetate from a shelf in 1903 and noticed how the shattered fragments stuck close together, laminated glass has had many applications. It was first used in the lenses of gas masks during World War I, and just before World War II, in the automobile windshield. The interlayer used was a flexible plastic sheet made of polyvinyl butyral (PVB), which could be sandwiched between glass. The PVB adhered well to the glass, was durable in terms of its weather performance, and maintained transparency in the car windshield application. The safety benefits-no shattering on impact -secured the position of laminated glass as an industry standard.

The use of laminated glass in buildings became more common as designers added skylights and built atriums and glass-enclosed walkways with canopies. The glass in these applications needed to be strong and withstand pressure from snow or high winds, and it couldn't shatter into pieces and fall on building occupants in the event of breakage. There were also other advantages to laminated glass in terms of reducing noise, the blocking of harmful ultraviolet rays, glare reduction, and even for protection against break-ins.

A turning point

However, architects and engineers found that to increase strength, making the glass panel thicker was often the only solution. And in some cases, the glass panels also had to be supported continuously on four sides to meet the load requirements.

Meanwhile, two trends were underway. One was that design professionals wanted to use glass in new ways, as stairs, floors, large overhead constructions, and curtain walls. But at the same time, glass had to be stronger than ever, because of evolving standards related to hurricane impact resistance. Rather than make laminated glass thicker, scientists began thinking that what was needed was an improved interlayer. A new, advanced polymer interlayer, or structural interlayer, was developed that was stiffer and stronger than PVB, and laminated glass entered a still-unfolding era of new applications and expanded design performance.

According to Dr. Stephen J. Bennison, Senior Research Scientist at DuPont, "Many structural engineers involved in the design of glass structures have readily embraced the performance benefits of the new structural interlayer." But, he said, "The advances in the laminated safety glass industry are often underestimated. There is a great deal of R&D going on that is related to extending interlayer performance beyond what PVB can do."

The interlayer imparts superior strength and stiffness without increasing overall laminate thickness. This strength benefit is so significant that glass panels may not need to be supported in the conventional four-sided manner anymore, enhancing the use of glass as a structural element. Laminated glass with advanced polymer interlayers is less sensitive to moisture on the edge and appears ultra clear, especially in combination with low iron glasses.