00:00What is polycarbonate and why can it be considered the unbreakable glass?
00:12Today we are going to talk about a material that you probably use every day, without even knowing it.
00:19It's in your cell phone screen, in your car's headlights, in the glasses you use for driving,
00:26and even in those CDs you still keep tucked away.
00:30We are talking about polycarbonate, a plastic as transparent as glass, but with an impact
00:35resistance that's up to 250 times greater.
00:40But how can polycarbonate material, a plastic, be more resistant than glass?
00:47That's what we are going to find out today, and to do that, we need to start from the beginning.
00:52The story of polycarbonate begins in 1898, when the German chemist Alfred Einhorn synthesized
01:02carbonate polymer for the first time in his laboratory.
01:07Despite the discovery, the material didn't find practical applications at the time, and
01:12ended up being abandoned for another half a century.
01:15It was only in 1953 that polycarbonate returned to the scene in a way that few could have imagined.
01:26Two independent discoveries in different countries with only a week between them.
01:32On one side of the Atlantic, in Germany, the chemist Hermann Schnell was working at the Bayer
01:40Laboratory in the city of Krefeld-Irdingen.
01:44He developed high molecular weight polycarbonate.
01:48From the reaction between bisphenol A and phosgene, and patented the invention that same year.
01:56On the other hand, in the United States, the chemist Daniel Fox from General Electric in Massachusetts
02:04was trying to develop a new material for electrical wire insulation, when, accidentally, he ended
02:13up creating a very similar polymer.
02:16Fox applied for the patent one week after Schnell.
02:21Since Schnell's invention date was earlier, the patent was granted to Bayer.
02:28But the two companies reached a sharing agreement and each marketed the material under its own brand.
02:36Bayer, under the Macrolon brand, and General Electric, under the Lexan brand.
02:42But what is polycarbonate?
02:45Polycarbonate is a thermoplastic polymer, which means it can be melted
02:50and molded repeatedly without losing its original properties.
02:56The name comes from the fact that its molecular structure contains carbonate groups along the
03:02entire chain.
03:04The carbonate group is formed by a central carbon atom bonded to three oxygen atoms.
03:11And it's this configuration that gives the material an unusual combination of mechanical strength
03:17and an object of transparency.
03:19Unlike glass, which is rigid and brittle, polycarbonate has long and flexible molecular chains
03:27capable of absorbing impact energy, distributing it over a much larger area instead of concentrating
03:36it at a single fracture point.
03:38But how is polycarbonate made?
03:40The most traditional process involves the reaction between two compounds, bisphenol-A and phosgene.
03:48Bisphenol-A is an organic compound derived from phenol and acetone, while phosgene is a highly
03:56toxic gas, which in fact was used as a chemical weapon during World War I.
04:02In the reaction, bisphenol-A is dissolved in an aqueous solution with sodium hydroxide, and phosgene
04:11is introduced into an organic solvent.
04:14When these two phases come into contact, what we call interfacial polymerization occurs, where
04:22the bisphenol-A molecules react with phosgene.
04:26Exactly at the interface between the two liquids, polycarbonate chains are formed.
04:33The resulting material is purified, dried, and turned into pellets that can later be formed
04:40by injection molding, extrusion, or thermoforming.
04:46Because of the risks associated with the use of phosgene, the chemical industry began to look
04:52for safer alternatives.
04:54The Japanese company Azahi Azahikazei developed and industrialized the first phosgene-free
05:01polycarbonate production process, using carbon dioxide as a raw material to produce diphenyl
05:10carbonate.
05:11And then it reacts with bisphenol-A in a melt polymerization process.
05:17This method not only eliminates the use of phosgene, but also reuses CO2 that would otherwise
05:25be released into the atmosphere as a greenhouse gas.
05:29And why is polycarbonate so resistant?
05:33The answer lies in the way its molecules respond to impact.
05:37When an object hits a glass plate, the energy from the impact is transmitted directly through
05:43the rigid structure of the material.
05:45Since glass doesn't have the ability to deform elastically, that energy concentrates at the
05:52point of collision and causes it to fracture.
05:55With polycarbonate, the situation is different.
05:58Its long polymer chains have the ability to slide over each other and deform temporarily, absorbing
06:07the energy from the impact and distributing it over a much larger area than the original
06:13point of impact.
06:15The energy spreads across the surface of the material instead of being concentrated in a
06:21single point.
06:22That's why polycarbonate is considered virtually unbreakable under normal conditions.
06:28with an impact resistance approximately 200 to 250 times greater than that of regular grass.
06:38And where else can we find polycarbonate in our daily lives?
06:42The applications are surprisingly varied.
06:45In car headlights, polycarbonate has replaced glass because it's lighter, more resistant to
06:52impacts from stones and allows molding into complex shapes that glass can't reproduce.
07:00In sunglasses and safety glasses, polycarbonate lenses offer protection against impacts that glass
07:09or acrylic lenses can't match, being required for personal protective equipment in many countries.
07:17In bulletproof glass, polycarbonate is used in overlapping layers, sometimes combined with glass sheets
07:26to create barriers.
07:28Barriers capable of stopping firearm projectiles, absorbing the kinetic energy of the impact through
07:36the controlled deformation of their layers.
07:39If you are over 30 years old, you have probably held a polycarbonate disk in your hands.
07:46CDs, DVDs, and Blu-rays were made with a 1.2 mm thick polycarbonate substrate, which serves
07:57as the base for the construction layer.
07:59The material was chosen for its optical transparency, which allows the laser to pass through the disk without
08:06distortion, and for its dimensional stability, which preserves the microscopic data tracks over time.
08:15In the construction industry, polycarbonate sheets are used in stadium roofs, residential roofs,
08:22and facades, because they are lightweight, impact-resistant, and easy to install.
08:29Even the shields used by security forces in riot control operations are made from this material.
08:38But does polycarbonate have any problems?
08:42Despite all its qualities, polycarbonate is not perfect.
08:46One of its main limitations is its susceptibility to scratches.
08:52Because it is a relatively soft material on the surface, it scratches easily, which may seem contradictory
08:59for a material so resistant to impacts.
09:03That's why in applications like eyeglasses and automotive headlights, it is often given a silicon-based
09:12hard coating to increase its resistance to abrasion.
09:17Another important limitation is degradation by ultraviolet radiation.
09:23When exposed to sunlight for prolonged periods, polycarbonate tends to yellow and lose some of its mechanical properties.
09:33To minimize this effect, UV stabilizers are added to the formula or protective coatings are applied,
09:42especially in outdoor applications, such as roofing and facades.
09:47And there is an issue that goes beyond the physical properties of the material.
09:51Bisphenol A, a fundamental raw material in the production of polycarbonate, has been the subject of extensive scientific
10:01study for its potential as an endocrine disruptor.
10:05That is, a substance capable of interfering with the human body's hormonal system.
10:12Because of these concerns, regulatory agencies in several countries have restricted or banned the use of bisphenol A
10:21in products such as baby bottles and food containers.
10:25The industry, in turn, began to develop versions of polycarbonate that use compounds as alternatives to bisphenol A,
10:35seeking to maintain the properties of the material without the risk associated with this compound.
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11:17Did you know polycarbonate was used in so many places?
11:21Have you ever needed to use a polycarbonate product and was surprised by its strength?
11:26Do you think it could replace class in even more applications in the future?
11:31Let me know in the comments because I want to know.
11:34Here on the site there are two interesting videos you should watch to expand your knowledge and satisfy your curiosity.
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11:46consider becoming a channel member.
11:48That's it engineering lovers, big hug and I will see you in the next video.
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