Brentwood Plastics blog

The Fine Art of the Sabotage Spec

Posted by Joel Longstreth on Sat, May 30, 2015 @ 03:21 PM

Sabotage specs are written wholesale every day.  Not much is written about why and how to write a sabotage spec.


The impetus for making a sabotage spec is obvious.  The agendas of supplier and customer are at loggerheads. As soon as an project is developed to the point of solving a problem, purchasing is itching to shop and start the reverse auction.  The path of least resistance is the sucker play - the ostensible need for a spec sheet.  This saves the time and expense of reverse engineering.  
Where's the rational incentive to divulge the ingredients and know-how ?
Two things are often overlooked at this juncture:
1.  questioning the premise of the need to know.  If there is no legitimate need to know how any ingredients might affect the customer's plant or product, there is no need to know.  It is naive to believe NDA's will be honored.
2.  is the distinction between a typical property sheet / data sheet and a specification sheet.  The latter is for the protection of the supplier to prevent arbitrary rejections.  A properly crafted spec has a target and range for specific properties.  The supplier has every incentive to keep proprietary how the properties are achieved. If it meets the criteria, the customer buys it.  If not, the out-of-spec materials are returned to the vendor.  In theory anyway.  What usually happens is the full shipment is rejected if part of one pallet is defective.  A typical property sheet is more generic public information.
In both cases, the description of raw materials and test methods is key.  It makes total rational sense to throw the competition off the trail with misinformation about raw materials instead of showing one's hand.

Two common tricks which nobody talks about are:

1.  proprietary test methods  Instead of abiding by standard test methods, simply state that your product exceeds with a proprietary test method.  For example, 3M states that their masking tape elongates more than everybody else's with their black box test method.  I witnessed firsthand 3M winning a bid at a higher price from the state of Ohio because no other masking tape had 11% elongation. 

2. fake values   Simply enter values which if met will not work.  This is guaranteed to waste your competition's time and give them a mental hotfoot.  The deck is stacked against the new candidate anyway because line personnel are an openly hostile audience.

Follow these simple tips and you will have a good chance of not getting shopped and putting sand in your competiton's gears



Did you know ?  " at loggerheads" is hundreds of years old.  A drink was made by combining rum and milk, then
heated by plunging a heated rod called a logger into the drink.  After a few too many, the logger was often used as a weapon.  The figure of speech connotes unresolvable conflict such as marriage and the middle east.


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Topics: spec sheets, sabotage spec, spec sheet, specification sheet

Homopolymers, Copolymers and Terpolymers - easy as 1, 2, 3

Posted by Joel Longstreth on Tue, Mar 31, 2015 @ 05:33 PM

The terms homopolymer, copolymer and terpolymer may sound like Latin or Greek.  They mean respectively 1,2, or 3 polymers.  This is sort of a misnomer as they are more like MONOmer building blocks conjoined through a reaction. 

Let's start with "polymer".  " Poly " comes from the Greek word for many.  As it pertains to plastic, it means many of the building blocks of monomers such as ethylene, propylene, styrene, etc. strung together in long chains to add up to polymers.

For more in-depth, visit our post on "where does plastic come from ? "

If the polymer is made simply from only one monomer, it is called a HOMOpolymer, or made from only one monomer.  POLYethylene, POLYpropylene, POLYstyrene, etc.  Far as I can tell, 1,2 Syndioatctic Polybutadiene is a homopolymer even thought the word is long.  Butadiene is the only monomer.

You guessed it - if there is another conjoined monomer ( not a mechanical blend ), you got a COpolymer.  Examples:  "ethylene vinyl acetate" or EVA for short - vinyl acetate monomer married to ethylene monomer, "styrene butadiene styrene" or SBS - styrene and butadiene building blocks,

A very cool copolyester is Eastman's Tritan.  Why it has not replaced glass on a major scale I do not understand.  I have some 5 year old tumblers which look like new.

And a TERpolymer is three monomers.  An oldie-but-goodie example is old fashioned phones which were made from "acrylonitrile butadiene styrene" or ABS.  Jump cut to present day - ABS is the default choice for 3 D printing.
A ubiquitous example of ABS is fake fingernails.



oldphone.jpgphoto courtesy of The Cathedral of Junk in Austin, TX

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Topics: polymers, plastic, copolymer, homopolymer, polymer, terpolymer

Visqueen  Construction Film

Posted by Joel Longstreth on Tue, Dec 30, 2014 @ 12:00 PM

We do not make Visqueen or any film in 100 foot rolls.   Please do not inquire.  Scroll down for a list of American "visqueen" film manufacturers.  Click this link for what we do manufacture.

Visqueen is another word for construction and agriculture, or "C & A" film usually in 100 foot rolls.  Visqueen, like "Frigidaire" and "Kleenex" is an example of what linguists call a secondary meaning or what happens when a brand becomes so commonplace that it is substituted for the original meaning.



Click here for a history.

Visqueen is used for non-critical applications not just on construction sites and farms.  It is the lowest end of the blown polyethylene film market. Any PE resin which can be extruded into blown film will do.  Cheating on weights and measures is commonplace.  Full gauge and width is an exception and nobody cares about weights and measures honesty.

Visqueen is often used to make makeshift greenhouses, but it will not last long due to degradation from UV rays.

It is commonly sold in 100 foot lengths in widths from 10 feet and wider in natural and black.

If you are looking for Visqueen / C & A film, here are links to some US manufacturers:


Did you know ?

The wonderful folks at the Ethyl Corporation who brought you leaded gasoline have never been sued for contaminating the ground with lead 

To create large pond liners, you have to splice big sheets of Visqueen film together.  In the olden days, they used to roll up dynamite fuses in the film and light it to make a seal.

The largest blown film line in North America is located at Poly America in Grand Prairie, TX.  Although Poly America's roots are in C & A film, their mainstay is private label trash bags.

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Topics: poly film, visqueen, construction film

No Plastic Clean Enough

Posted by Joel Longstreth on Tue, Oct 28, 2014 @ 12:55 PM






What is it about the connotation of fossil fuels anyway ?  Are we supposed to just accept the premise that fossil fuels are bad a priori ?   I know when I'm winning an argument with a green when they say "you're still usin' fossil fuels, man."

Plastics bashing is a popular indoor sport with proponents of green building materials.  Has any one of them led by example and founded a plastic company which scores 100 ?

Breakfast TV emphasized that a burning railcar of chemicals in Tennessee contained a chemical used to make plastics.  The chemical was acrylonitrile, a building block of acrylonitirile / butadiene / styrene, or ABS for short.  Ironically, the equipment used to film, edit and broadcast this news contains many parts made from ABS.

There is a definite trend with large corporations to avoid Chemicals of High Concern ( CoHC's ) by avoiding the controversy if at all possible.  We have to spend a lot of time documenting what our plastics do not contain.    Anymore, marketers emphasize what their product or packaging does not contain even though manufacturing has changed nothing.  Call it greenwashing, eco-labels or the Culture of Alarmism.

We could get with the trend and unabashedly emphasize so many things starting with our feedstocks.  We could say our plastic is derived from free-range, cage free, fair trade natural gas for starters.  We have to certify that our plastic made in St. Louis is not made with slave labor, so we got that going for us too.

Natural gas is naturally non-GMO, BPA free, phthalate free and gluten-free too.








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Topics: clean plastics

What is poly LDPE shrink film ?

Posted by Joel Longstreth on Thu, Jun 19, 2014 @ 05:50 PM

Plastic shrink wrap is thermoplastic extruded and oriented so that when exposed to heat, it retracts and tries to return to it's form prior to being oriented.

There are many varieties of shrink bundling films.  They range from clear, thin shrink films for retail packaging to thick, heavy duty industrial shrink wrap.

High end light duty shrink films are generically known as " olefin " films.   Olefins literally mean the lighter molecular weight parts of a barrel of crude oil ( naptha ).   How this misnomer became to applied to shrink films is anybody's guess.  Most commonly, PVC or polypropylene is blown into a bubble, reheated and blown up again, hence the slang " double bubble " label for these films. is an example.

This is the poor man's version of Clysar pioneered by DuPont.  It is a multilayer film which is not only reoriented, but irradiated as well.  The molecules are in a very "excitable" state, making them very sensitive to heat.  These shrink films are also known as " low temperature shrink" in the meat industry.  They respond well to exposure to a tepid, not even boiling, water.



The verbal shorthand for the thickness of olefin films is referred to as " ______ gauge ".  All you have to remember is that every mil = 100.  If you hear " 60 guage" it means 6 / 10 of a mil.

Polyethylene films with the exception of printed beverage films, are more like workhorses and not as glamorous.  In terms of thickness, they pick up where olefins leave off.  They are not as clear as olefins.  The shrink ratios, or amount of shrink in the machine direction ( MD )  and transverse ( TD ) directions cannot be manipulated.  Practically speaking, about 20% TD shrink is the best one can hope for.  MD shrink is stuck at about 65%.

Watch this video to learn how to test heat shrink plastic film ratios in both MD and TD:

Because of the high amount of TD orientation, olefin shrink films have "balanced" shrink in both the MD and TD.

Industrial shrink bundling film is for unitizing cans, bottles and bags.  It's natural habitat is ubiquitous in supermarkets in the early morning when shelves get stocked. 

Plain PE shrink film is the dumping ground of polyethylene film.  It is a convenient place to blend in scrap and rip off customers who do not know or care how to check on weights and measures. Learn how to keep your PE film supplier honest about weights and measures by watching this video:

The low per pound or roll price looks good in the office and results in inconsistent performance in the plant.

Here's a link to what most PE film extruders and distributors don't want you to know:

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Topics: shrink film packaging, plastic shrink wrap, what is shrink film

What Plastic does not contain is most important

Posted by Joel Longstreth on Tue, Apr 29, 2014 @ 05:02 PM

The metastasizing list of chemicals we must certify that our plastic does not contain is growing.  To say it's absurd is an understatement.  Where does it end ?

Back in the 60' and 70's, it was commonplace to get orders for FDA repro ( reprocessed ).   Flash forward to last week - before we could participate in an RFQ, we had to certifiy that our film complied with ROHS, CPSIA (consumer product safety improvement act of 2008 ), CA prop 65, TPCH toxics in packaging clearing house,  as well as BHT, BPA and latex free.  

Wait - there's more !   We had to certify to a bread bag maker that our films are gluten free.  After 43 years.


It's hard to square this concern about purity when there is apathy about dermal contact with lead if the price is right  Every day, thousands of feet of yellow barricade tape containing 1% lead is handled on fingertips and disposed on the ground in California.

FDA approval is meaningless anymore  

Our Kosher approval letter ( an annual process ) and biotoxicity tests still aren't enough assurance in many cases.

I didn't know how to deal with this conundrum until inspiration struck at the health food aisle.  We should take a page out of the greenwasher's and health food marketer's playbooks.  Just do what you always have done and say it's green and healthy.  Shazam !

There are so many positives about what our plastic does not contain that it's hard to decide where to begin.
contains no yeast, dairy, egg, soy wheat, sugar, fructose, starch.  Cruelty free, cholesterol free, no trans fat, no MSG, BPA free, no BHT, gluten free, no trees or plants cut down ( vegan,right ? ), no GMO ingredients, no lead, no cadmium, 

What about free range cage free ?  The plants and dinosaurs which became our natural gas feedstocks were not raised in cages.

Note to self:  check into getting non GMO project verified.


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Topics: plastic additives, plastics toxic

Plastic Film Property Trade-Offs

Posted by Joel Longstreth on Tue, Apr 22, 2014 @ 05:46 PM

Plastic FIlms like many things, trade off one property at the expense of another. 


If polyethylene film has not been your life, take 2 minutes to learn the 101 for background.

for example -

if you want these properties in the same film        it's not going to happen because
stiff and low melt point                                                melt point is a function of density
soft and high melt point                                               higher density = stiffer, higher melt point
                                                                                    lower density = softer, lower melt point

fast tack and low seal intiation point & stiff                 molecules become more crystalline as density increases

clear and soft                                                              lower density is tacky.  Antiblock is necessary to prevent
                                                                                    blocking on the roll.

Melt Index Most of the trade-offs can be grasped with a rudimentary understanding of the two most basic influencers of a resin's personality which derive from a geeky term called molecular weight distribution -  melt index and density.

It seems intuitive that a resin which is very viscous ( hard to push ) is going to be strong.  An extreme example is the resin used to make Tyvek and those t shirt bags the greens love to hate.  It is forty times harder to push than your garden variety bread bag resin.   Strong, but not clear.    At the other extreme, a hot melt resin which is 700 times less resistant to flow than bread bag resin has no strength.

Density derives from crystallinity.  At the upper extreme, high density (  HDPE ) is very stiff ( think milk carton ) and requires a lot of heat to get it to flow into the mold.   At the lower extreme ( VLDPE and ULDPE ) it takes minimal heat to initiate a seal because of low heat resistance and minimal crystallinity.

Even metallocene is not exempt from these laws.

These factors must be considered when sealing film from one blown film extruder to another.  It's a wild-card scenario. If the 2 resins are too dissimilar they will not seal.  The new film is always blamed for poor seals.  If there are bad seals, no problem.  Don't pay for it.  There are plenty of other places to get film.


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Topics: PE film properties

Creep in PE films

Posted by Joel Longstreth on Thu, Mar 06, 2014 @ 04:26 PM

Creep is the tendency of a material to flow in the solid state.  Wikipedia defines it more accurately as deformation  

The rate of deformation is time and temperature dependent.  No surprize there. Viscosity, or how resistant a material is to flow dictates how susceptible it is to creeping ( think molasses vis a vis kerosene ).


An example we have all encountered is old pressure sensitive tape.  The side of the roll is tacky and the roll exhibits dishing, or "telescoping" if it has had continuous pressure on it.  The adhesive has flowed, albeit slowly. Some tapes require a separator sheet made from release liner to keep the sides of the rolls from sticking together.

As creep applies to polyethylene, higher density PE is more rigid and not prone to distortion due to heat and pressure.  Linear low density polyethylene ( LLDPE ) is more susceptible to creep than conventional PE especially at lower densities.

Back in the early days of LLDPE, it didn't take long for shipping sack manufacturers to learn that the laws of physics imposed limitations on downgauging, or thickness reduction.  The bottom layers of pallets of mulch and soil bags under 3 mils actually ballooned over the side of the pallets, making them inaccessible to forklifts. 

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Topics: PE film properties, PE film creep

Melt Fracture in PE film

Posted by Joel Longstreth on Thu, Mar 06, 2014 @ 04:09 PM

Melt fracture a/k/a "sharkskin" or "applesauce" occurs in LLDPE film.

melt fracture polyethylene film LDPE

To say that much has been written on the subject is an understatement.  Entire books and dissertations abut melt fracture have been written by polymer chemists a lot smarter than me.  Still there is not total agreement on the causes.  Personally, I have a hypothesis that it has something to do with susceptibility to degradation in the transition section of the screw.  


Going back to the early days of LLDPE melt fracture was just expected in butene LLD but not Octene.  Carbide advocated a return to shorter L/D ratios for shorter residence time.  This and granular resin never really took off.

No matter the cause, melt fracture results in a very irregular scaly texture to the film.  In most cases, this is considered an undesirable quality because it detracts from the cosmetics.  In a few cases such as forearm protectors it is considered a plus but i don't know why.

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Topics: LLDPE melt fracture

Yellow Dye Concerns, Lead Apathy

Posted by Joel Longstreth on Mon, Feb 24, 2014 @ 04:15 PM

Consumers are apathetic about dermal absorbtion of lead if the price is low enough.

Absorption of yellow dye may result in a variety of maladies.  Of course, more research money is needed but in the meantime we should be concerned.

Meantime, we seem to be apathetic about dermal absorption of lead if the price is a bargain.

We had yellow caution tape from China tested a few years ago.  It contained one percent lead. That's 10,000 parts per million.  Thresholds for exposure to toxins are usually expressed in hundreds of parts per million max.


Consumers prefer it over the heavy metal free plastic we make here in the US because it is a lot cheaper.
The conscious choice is made daily to expose one's fingertips to lead.  

75 FR 44463 bans lead in excess of 100 parts per million for the protection of children.  Adults are on their own to make an informed choice.

How can this be ?  The law of the land since 1978 in 16 CFR 1303 bans paint containing lead but not lead in the materials the painters, construction workers and first responders use.

Sell or rent a house these days and you get several pages from the EPA's brochure about protecting your family from lead in your home even if the house was constructed after 1978.

The EPA tells us lead poisoning is preventable even if your home was built before 1978

Does this mean we are myopic or apathetic if the price is right ?

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Topics: yellow dye dangers, lead in toys, lead poisoning,

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