PCTG – polycyclohexane dimethyl terephthalate modified by glycol

PCTG? My wild guess was polycarbonate technical grade. I was terribly wrong. Its expanded name is rather long that I never want reading and pronouncing. I feel like practicing a tongue twister. It is “polycyclohexane dimethyl terephthalate modified by glycol”.

Created in response to BPA issue. Not sure when and I am too lazy and too busy to dig.

Is it really BPA free? Wait until concerned institutions conduct their thorough studies. For the time being, let’s use it with no worries. Pretend that the only bad thing in plastic is BPA, none other.

According to emmarco.com, it has excellent toughness and good heat resistance at ~120˚C. It is food safe as granted by FDA, and so will not emit BPA. Generally priced about 20% higher than PC.

The same appearance and feel of common polycarbonates, the “other plastic”. I am not talking about the pure and high quality polycarbonate here. It resist squeezing. I did not try too hard to avoid intentional damage. I want it whole and sound for my new project.

It seems that not all PCTG are created equal. There are different types with different properties. Here is what I found on ptonline.com. Take note of the code “DN010” and “MN005”.

Also new from Eastman is DN010, an injection moldable PCTG with high clarity (92% light transmission) and toughness suited to replacing acrylic. Higher toughness reduces breakage and permits snap-fit designs. Another new PCTG for injection molding is MN005 for clear medical devices and packaging. It has double the normal flow rate while minimizing trade-offs in impact strength and elongation.

Going on…

My project requires cutting holes on bottom and side. I was very careful at first to prevent any unnecessary cracks. However, it proved to be very tough and took me a long time. I use more brute force for next bottle and I did it in half the time. Nice clean cut with no cracks. I think, its toughness is comparable to PET.

As of the moment, there are very few details about this polymer.

Various Tests on PET Peanut Jar

peanut jar with cocoa nibs

I did a few tests on this packaging material before, the peanut jar. Leak test, failed. Half-filled the jar with water and shook it. Water droplets were spilling out. It was not conclusive, however, I never used appropriate bottle seal.

Appropriate seal? The jar lid should be sealed using induction sealer with appropriate seal for this plastic. This PET perhaps so the seal should be made specifically for it.

Lukewarm water test. The bottle can hold itself well. Fair enough, barely hot water can never harm human skin, what less to a PET type plastic.

Hot water from a thermos. There was a slight deformation after few minutes. And that modest is unforgivable. It might affect the lid resulting to faulty seal. Disruption to structure might have also caused migration of plastic molecules to contents.

The last was hot water steam test. Held the bottle with the lid facing down the rushing steam. It shrunk so suddenly to unusable state, just like a flattened canned softdrink. It won’t budge if it was heat set.

So I concluded. It cannot be used for hot-packing products, but very much suited if allowed to cool to acceptable level. However, I found something interesting recently. The cocoa nibs that I packed in, tasted and smelled like plastic. It was faint, but may not in senses of sensitive buds. For me, it was awful, masking the original delicate flavors.

peanut jar with cocoa nibs

I bought samples of this PET jars to package our product cocoa nibs. We ended using the clear stand-up pouches. The latter is cheaper, look as good, easy to seal with impulse sealer and easier to handle.

A Wider and More Comfortable Wilkins Bottle Handle

Was I lifting a 6-liter Wilkins bottle? I thought not but it was really Wilkins. I had the feeling it was lighter. Hmm. Do you know what made me think it was not?

All 6-liter mineral / drinking water in PET packaging come with a feature similar to handbag. Any buying customer can carry it on the spot without putting it in another container, a sando bag, hand bag, bayong or similar. If the feature never exist then the normal thing to do is to place it in carrying bag, grip it underarm or hug it with both arms.

However, an average human can carry it only for a relatively short distance. The weight together with the narrow handle tend to strain the hand easily. Buyers taking a long walk are gripping it underarm, hugging it with both hand or placing it on shoulder. The manufacturer realized this and made the bottle handle twice as wide for customer convenience.

Given a constant weight, the one with wider handle feels lighter and more comfortable to carry.

wilkins pet bottle handle comparison

I think making it wider, about one inch, and rounder is a nice step.

Unknown Gas Coming Out of PET Bottles

The night was getting deeper and the surrounding was getting silent. Neighbors were turning off their television sets, radios, computer. They were going to sleep. The same was happening to our home. However, I have the habit of staying awake even if most people around me are sound asleep.

The surrounding was silent. I was hearing clearly the wall clock ticking sound, including a strange low knocking sound which I could not determine the source. I was sure it was somewhere near my seat. I have been hearing it and looking for it for several nights.

Accidental discovery. I filled my glass with drinking water from the Tang litro pack. After, I saw the flip flop cover popping up accompanied with the low knocking sound. So this PET bottle was the culprit. It was the thing capable of making low noise by itself. It was popping about every five seconds.

tang flipping flip top covertang flipping flip top cover open

I am wondering why. I have the idea, PET bottles reacts with its contents with repeated use. The force that was making the flip cover open partially and make a knocking sound was a gas build up. The easiest scape route was the loose flip cover. The idea of PET polymer reacting to water and other foods is acceptable to me but the gas production is simply unbelievable.


The Tang and Nestea Litro Pack PET Bottles

These two plastic bottles have common denominators.

neastea and tang pet bottles

* They were both came from promo. Free items from buying certain juice brands. The smaller from Tang Litro Pack. The bigger was from Nestea Two Litro Pack. I think, Tang also released Two Litro Pack. It so happened that we were not able to catch its promo.

* They are both meant as juice preparation container. Each has its own instruction set.

* Both can be use as baon pack (juice on the go). Prepare the juice according to instructions. Cover it and you are ready to go. Please carry it carefully to avoid any spillage!

* Both are PET bottles. The same polymer type use for manufacturing softdrink and other ready-to-drink containers. Heat resistant in most cases but not meant for hot liquid. The Nestea Two Litro Pack has a reminder not to fill any hot liquid.

* As with my experience with PET bottles as storage of drinking water, it tend to impart off-taste to its contents after repeated use.

* I think, they should have manufactured PP, polypropelyne polymer instead. It is more resistant to scratches thus maintaining its elegance longer. More stable to heat and other substances and thus causing less off-taste problem.

Identifying a Plastic Container with no Recycling Symbol

In case the factory failed to place a recycling symbol on plastic bottle or container, it can be identified by following the simple tests.

1) Water test. Force a piece of polymer under water. Wait and see if it is a floater or a sinker.

2) Water floater test 1 – alcohol test. Force several pieces in 45.5%(by volume) alcohol solution. HDPE(2, High Density Polyethylene) if sinker, continue to floater test 2 otherwise.

3) Water floater test 2 – oil test. Force several pellets in corn oil. LDPE(4, Low Density Polyethylene) if sinker, PP (5, Polypropylene) if floater.

4) Water sinker test 1 – copper wire or burn test. Place a piece of copper wire against flame to make it red hot. Then punch it immediately to polymer to grab a small portion. Bring back the copper wire on flame and observe flame color. Green flame means PVC(3, Polyvinyl Chloride). Continue to next test if flame is orange .

5) Water sinker test 2 – acetone test. Submerge a pellet in acetone for 20 seconds. Softened and sticky surface is a positive reaction. PS(6, Polystyrene) if positive, continue to next test otherwise.

6) Water sinker test 3 – heat or water boiling test. Place piece of polymer in water and boil for 30 seconds. PET(1, Polyethylene Terepthalate) if softened. Might not give accurate results due to popularity of heat resistant PET bottles.

Note: All above test were courtesy of David A. Katz, 1998. Advancement in polymer manufacture might give inaccurate results.

The test procedure for code 7 plastic was not included. No simple test are available cause this group is a mix or collection of all others. Mostly made of polycarbonates or abs.

I found useful information on boedeker.com. Place a piece of polymer against flame source for 10 seconds and observe. If polycarbonates – burn test results to faint sweet aromatic ester odor, orange flame color, with drippings. It produces black smoke with soot in air.

On the contrary forum from eng-tips.com said that polycarbonate produces oily or acrid odor on burn test (thread712-184534: how can I tell what type of plastic?)

If acrylonitrile butadiene styrene, ABS. Produces acrid odor, yellow flame with blue edges, no drippings. Able to continue burning after removal from flame source. It also produces black smoke with soot in air.

I gonna collect code 7 bottles to conduct tests.

Baby feeding bottles made of group 7 are often rigid that it cannot be pressed in between fingers. PP bottles or group 5 are more flexible.