Safety glass laminates: the interlayer that holds broken glass fragments in place during an impact, reducing injury risk, is primarily which polymer?

Introduction / Context:
Laminated safety glass used in automotive windshields and architectural glazing comprises glass–polymer–glass sandwiches. The interlayer must adhere strongly to glass, absorb impact energy, and hold shards together upon breakage. The industry-standard interlayer is polyvinyl butyral (PVB).

Given Data / Assumptions:

• Target properties: adhesion to glass, toughness, optical clarity, and durability.
• Processing requires thermoplastic film lamination under heat and pressure.

Concept / Approach:
PVB, derived from acetalisation of polyvinyl alcohol with butyraldehyde, offers excellent adhesion to glass (especially with appropriate plasticisation and moisture control), high impact resistance, and optical transparency. While other interlayers exist (e.g., EVA, ionoplasts) for specialty glazing, the classic and most widely taught material for safety glass is PVB.

Step-by-Step Solution:

Verification / Alternative check:
Automotive and building codes, as well as supplier literature, consistently specify PVB for laminated safety glazing, with standardized thicknesses (e.g., 0.38 mm, 0.76 mm).

Why Other Options Are Wrong:

• PVOH: hydrophilic; poor durability as a neat interlayer.
• Polyvinyl acetale (generic): vague; in practice, the butyral acetal (PVB) is used.
• PVC: plasticiser migration and optics limit use as a safety interlayer.
• EVA: used in some specialty/photovoltaic laminates but not the canonical answer.

Common Pitfalls:
Confusing generic “acetals” with the specific butyral derivative proven in safety glass.

Final Answer:
Polyvinyl butyral (PVB)