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Category: Educational (Page 1 of 14)

Educational topics and useful things to know.

Saran Wrap Isn’t What It Used To Be

In the 1960s, I used to help my mother in the kitchen and learned how to cook. I used Saran Wrap to cover plates and bowls, and I noticed that this material was sort of magical. It stuck to what I wanted it to stick to and wasn’t much inclined to stick to itself. What is this sorcery? You could pull it back to access something in a bowl, then seal it back up again. I was fascinated because it seemed like it was intelligent. I had studied some chemistry but not yet enough to guess the cause for this marvelous behavior.

So what was this wonderful material I was working with? In 1933 a chemist at Dow Chemical was trying to develop a new dry cleaning solvent. He noticed that certain beakers and glassware were hard to clean. They had a residue that was hard to scrub off. Investigation revealed a new substance, a new polymer that was named polyvinylidene chloride or PVDC.

It was found that, among other things, PVDC made a tough and durable clear coating. During World War 2, virtually every U.S. aircraft was coated with PVDC to help protect it from the elements. At the end of the war, hundreds of companies in the U.S. got busy looking for commercial applications for the countless marvelous things they had developed for the war effort. Somebody at Dow realized that PVDC would make an excellent food wrap. And excellent it was, as you will see later. Production methods for forming PVDC into a very-thin film were developed. The CEO of Dow decided to name it after his wife and daughter, Sarah and Ann: Saran.

The product was introduced in 1949 and was an almost overnight success. This is the stuff I was using in the 1960s. Towards the end of the 1960s, Dow’s patents expired and other companies began producing PVDC food wrap, like Glad Wrap. They were all just copies of Saran Wrap.

From the 1990s forward, I didn’t use much plastic food wrap until I began to work in a restaurant in 2012. There, I used plastic food wrap all the time and immediately noticed that it behaved differently from what I remembered. Sure, it worked, but it frequently refused to stick to some things and it was eager to stick to itself. This is not what I remembered. After opening and closing a covered bowl, the plastic wrap would become wrinkly and refused to stick to anything. I covered a mixing bowl full of diced onions with this plastic wrap and placed it in the cooler. Soon, the cooler smelled strongly of onions. What? That’s not supposed to happen. What is this stuff? Maybe some kind of cheap imitation of Saran Wrap?

Time passed, I finally did some digging on the Internet, and immediately found the answer. Through the 1990s, chlorinated polymers like PVDC became an increasing environmental concern. In 2004, all the makers of PVDC plastic wrap switched to ordinary low-density polyethylene (LDPE). Polyethylene is cheap and easy to make into a thin film. But there are problems. Big problems.

First of all, polyethylene is a low-friction, non-stick kind of polymer. This is why milk bottles are made from it. Polyethylene film doesn’t stick to anything, nor itself. Today’s polyethylene plastic food wrap is coated with a moisture-activated adhesive to make it “cling”. At best it clings to certain things but not others, and it eagerly sticks to itself, making it hard to work with.

Secondly, the adhesive quickly wears out so opening and reclosing a bowl covered with modern plastic wrap is something you might be able to do once but not repeatedly, like you can with PVDC film.

Thirdly, polyethylene film is around 3,000 to 4,000 times more permeable than PVDC film. Oxygen is the main culprit that causes food spoilage. For every one molecule of oxygen that a given area of PVDC film lets through, polyethylene film lets through 3,000. The consequences of this are obvious. This also explains the experience I had with onions stinking up the cooler. That wouldn’t have happened with PVDC film. In fact, certain meats are still packed with PVDC film because polyethylene film can’t do the job.

The bottom line for me is that I was pleased to discover that my memories from the 1960s were pretty accurate. However, I was not pleased to discover that the plastic film I use today is inferior in terms of performance and user friendliness, and there’s no way to fix it.

Today’s plastic wrap looks like classic Saran Wrap, but it ain’t. It’s not even close.

High-Performance Masks

High-performance masks are now available.

Example high-performance mask

High-Performance Mask

High-performance masks are made to a specification that significantly exceeds the filtration efficiency of industry standard N95 masks. They deliver twice the filtration efficiency, and on particles down to 10 nanometers, which exceeds NIOSH N95 requirements by a factor of ten. All masks are equipped with a robust non-springy nose wire that can be shaped to seal to your face and nose.

If you want a reusable mask that looks nice and outperforms industry standard masks, you have found it here. They look the same as the standard masks but weigh slightly more because they contain three layers.

How do these masks work? In April of 2020, six researchers decided to collect samples of numerous fabrics used to make reusable masks and measure their filtration efficiency with the same equipment used to test industry standard masks like the N95. Since the topic here is viruses, the researchers enhanced the testing setup with a particle generator producing particles down to just 10 nanometers in size, making the test exceptionally demanding. (A Covid-19 virus ranges from 80 to 100 nanometers in size.)

Cotton, flannel, silk, and other materials were tested at 1, 2, and 4 layers, and then in various combinations. The researchers expected a cotton/silk combination to perform the best because of the electrostatic interaction between the two materials. Cotton/silk showed 92 percent efficiency. Howver, the researchers discovered that cotton plus 90/10 chiffon performed even better, reaching 97 to 98 percent efficiency.

This work appears in a peer reviewed scientific paper published by the American Chemical Society here:

https://pubs.acs.org/doi/10.1021/acsnano.0c03252

High-performance masks are made with an outer layer of high thread count cotton, an inner layer of 90/10 chiffon, and a comfortable inner layer of cotton muslin like the standard masks.

Get them here: https://www.ebay.com/itm/254577982386

Coronavirus Covid-19 Quizzes

In the interest of getting more information on the Covid-19 virus out and in easily digested form, I’ve developed three educational quizzes. Those quizzes have been added to my existing quiz web site.

The Covid-19 virus is new and much is being learned. New discoveries are made and our knowledge refined every day. There are changes in what’s known every day. In compiling information for these quizzes, I found many examples where information published a week or two ago is already obsolete. These quizzes are based on the best information I could find as of March 18, 2020.

I will do my best to keep these quizzes up to date. Please comment here on this blog post with any updates or incorrect information you may find. Ideas for additional questions or additional quizzes are welcome. In fact, this blog post exists so that you have a place to leave comments.

Click here to go to the quizzes.

My Vote Counts More Than Yours

In presidential elections, not all votes are equal. Wait. What? But, this is a democracy — one person, one vote, right? No.

Two hundred years ago, the founders designed a presidential voting system that gave rural farmers and ranchers in states with low population more voting power than people in urban areas. Among other things, the Electoral College was designed to try to avoid a tyranny of densely populated urban areas over other, less populous, areas of the country. It worked okay through the 1800s and most of the 1900s. But, the founders never imagined an organized, scientific effort to take advantage of the voting power imbalance in order to seize power.

So, exactly what are the numbers? The power of a voter in Wyoming is almost four times that of a person living in Texas. Whether this is fair and appropriate is for you to decide. See below for how much your vote counts.

Presidential Voting Power in Each State

 

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