Mad about Science: Latex Gloves

By Brenden Bobby
Reader Columnist

My hobby involves going through a large number of latex gloves. Photopolymer resin is really bad for your skin, so you need to use gloves to handle the stuff when processing resin-based 3-D prints.

Don’t worry, we don’t use resin at the library and your PLA prints are perfectly fine to handle barehanded. The resin printer I use is for highly detailed miniatures, which require far more detail than extruded PLA can provide.

This led me to wondering how they mass-produce nitrile and latex gloves, and when they were invented.

Hands are pretty complex appendages. Everyone’s hands are shaped differently, so it isn’t realistic to mold a user’s hand and tailor mass-produced gloves specifically to them. Instead, a manufacturer has baseline hand molds that vary in size to produce a product that fits well enough for everyone. The latex glove only needs to act as a barrier to keep unwanted chemicals or pathogens out; it doesn’t need to be a perfect fit.

It all begins with latex. Latex comes in two forms: organic and synthetic. Organic latex comes from the milky-white sap of the rubber tree. Hevea brasiliensis, which is harvested from plantations in South America and Southeast Asia. The natural latex is hardened into durable rubber through vulcanization, which uses sulfur and heat to create dense polymer bonds within the latex. This makes it extremely useful for a wide variety of applications, from car tires to surgical gloves.

Organic latex has a long history, having been used by the Indigenous peoples of South America for at least 1,100 years, though without the process of vulcanization. That was discovered in 1839 by American chemist Charles Goodyear, for whom Goodyear tire is named. Goodyear, the chemist, wasn’t actually involved with the founding of Goodyear the company. It was named after him, four decades after his death, by the entrepreneur Frank Seiberling.

Synthetic latex comes from mixing two chemicals: styrene, often seen as expanding polystyrene or styrofoam packing material; and butadiene. Both of these chemicals are extracted from crude oil and, when combined, form a synthetic rubber. This is especially useful for countries that are far from rubber plantations but have access to crude oil. Before World War II, these were the driving factors for many countries seeking synthetic alternatives to rubber based on the fear of being cut off from organic rubber supplies by the British Empire. After all, the British controlled most rubber plantations in the world at that time through its numerous scattered colonies.

Returning to the manufacturing of latex gloves, preparing the liquid latex isn’t actually the first step of the production process — that involves getting the hand molds ready. Each line has a conveyor system in which thousands of hand molds are suspended from the conveyor to undergo several processes before the glove takes shape. At a distance, it looks like some kind of nightmare facility where thousands of disembodied hands are just hanging around.

The first step is to clean the hand molds by dunking them in an acid solution, then soaking them in water, blasting them with air, drip-drying them and then heating them in an oven. The molds are then submerged in calcium nitrate, often used as fertilizer, which acts as a coagulant to which latex will stick, as well as being an important part of the demolding process later. After this step, they are dried again and then are dipped in a tank filled with blue liquid latex. 

The blue or green colors are not random — they’re specifically chosen for several specific reasons. These colors have high contrast to traditional hospital environments, as well as human skin. This makes it easy to spot rips in the glove before or during a procedure. I can attest to this one, as I usually spot the rip in the glove before I feel open air on my skin, prompting me to swap gloves before processing any more resin. Additionally, these gloves help reduce eye strain on surgeons, who spend a lot of time looking at the color red, as macabre as it is. Blue and green oppose red on the color wheel, allowing a surgeon to easily differentiate between their own hands and the patient they’re working on, even when their hands are covered in the patient’s blood.

The first layer of nitrile latex is dried in a long oven, and then they are dipped again to compensate for any bubbles or deformations from the first dunk. They’re dried again, and then fed into the hemmer, which is a series of textured rollers that texture the hem and push the latex up the mold to form the hem that you grab for removing the gloves once they’re on your hand.

The molds go through several more water baths, a chlorine bath and two more sets of drying ovens before they reach the pre-stripping stage, where a roller presses up the hem of the glove to prepare it for peeling from the mold. 

The stripping machine has little grabber mechanisms that pull the glove to the fingertips of the mold, allowing them to hang free before reaching the final stage, which is a machine with two round grabbers that automatically counts the gloves and peels them off, depositing them into stacks for workers to pack into boxes for shipping.

Stay curious, 7B.