Brentwood Plastics blog

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 ?

Read More

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

BHT in Polyethylene Film

Posted by Joel Longstreth on Tue, Feb 18, 2014 @ 05:18 PM

Customers continue to ask us for assurances that our PE films do not contain BHT.  The reason they ask is that BHT makes film printed white turn yellow.  When exposed to light, the yellow turns white again.

We just got another one of these inquiries.  To understand it chemically and to have it explained in 10 year old English, I asked our guru - Mr. Rudy Bourgeois of the M Holland company.

His response:

"BHT especially makes white print turn yellow due to the iron content in the white masterbatch which acts as an accelerant to the reaction described below:

BHT was used years ago as an A/O agent.  It has a low molecular weight and a relatively low melt point, which made it ideal for protecting PE resin during extrusion.  The downfall of this phenolic A/O is that it migrates and reacts with the lignins in paperboard and also with the exhaust gas from forklifts to form a compound called stilbene quinone.  This compound is crimson color in concentrated amounts and yellow in diulted amounts.  

It is a reversible reaction and will go clear again when placed in sunlight for a while."

So now we know.  Thanks, Rudy !

Read More

Topics: BHT, BHT in PE film, BHT free

PE film tin canning

Posted by Joel Longstreth on Fri, Feb 14, 2014 @ 04:13 PM

polyethylene film tin canning
"Tin canning" describes the longitudinal ridges which often appear in low density LDPE polyethylene film - usually blown PE film.
For many applications of PE film, tin canning does not matter.  Heat shrink film is one example.  The ridges smooth out when the film shrinks.  Same goes for industrial box liners.  Not so for film which gets printed, laminated or coated.  These demanding processes require a perfectly smooth " lay flat" film.  Any film with a slight indication of tin canning ( usually by the pressman who taps at points across the roll looking for a slight marshmallow like surface ) gets rejected before it gets put on the press, laminator or coater.
Of course only the blown film manufacturers care about the causes of tin canning.  Customers just want flat PE film.  Here are some factors which can contribute to tin canning:
resin selection
a no slip / antiblock only film with a high COF will not "settle" after being wound up
thinner films will get stretched more on the way to the winder, exacerbating any imperfections in gauge profile
treated films with their higher surface energy tug at the interfaces of the layers on the roll
wider webs have more area across the web
While the main culprit is excessive winding tension which stretches the film and does not trap microscopic pockets of air in the roll, you might have to live with occasional tin canning if you call out a no slip, wide, treated PE film.
Read More

Topics: LDPE film, PE film tin canning, blown film extruder, tin canning

PVC replacement is complex

Posted by Joel Longstreth on Fri, Sep 27, 2013 @ 05:12 PM

 PVC replacement is not as simple as finding a polymer which passes the "duck" test at a lower price.  PVC substitutes require workarounds because PVC has unique characteristics.

PVC is not inert.  It reacts with solvents found in inks and adhesives more than simpler inert commodity polymers.  Inks and adhesives which have evolved to be compatible with vinyl will not have the same results when a different plastic film is dropped in.  If we've heard it once, we've heard it literally dozens of times - " your PVC substitute is no good; it doesn't act exactly like our heirloom vinyl."  Nobody wants to have to bring in different inks, different adhesives, change the line speeds, drying conditions and embosser settings because they love mother gaya.  

If there's a volume buyer who is willing to pay a green premium, we have yet to meet them.
Billboard printers process truckloads of PVC film daily.  Nobody ever asks where the used billboards end up ( answer: in the landfill where they degrade into chemicals we don't like to talk about ).

RF welding is the same script.  PVC is what is known as a "polar" molecule.  It responds to radio frequency waves, hence the name RF for short.  The radio waves induce the molecules to start spinning.  This creates friction and welds from the inside out - the complete opposite of heat sealing which is done by heating from the outside.  Other polymers such as urethane react similarly, but not anywhere near as much as PVC.  Non - polar plastic films are anathema to established RF welding shops who are not about to make capital investments until their hand is forced.  

The scrpt is always the same.  The play has three acts with a run time of about 120 days.

Purchasing searches for a PVC replacement because a major customer who has been forced to eliminate PVC might be lost.  Specs for PVC are proferred to potential vendors along with promise to make minor tweaks to manufacturing process if necessary and to pay a green premium.


Suppliers submit candidates for evaluation.  Performance properties mimic PVC as closely as possible.Minor tweaks turn out to be major capex requirements, line personnel are hostile and reluctant to make adjustments. After the third iteration, all parties are frustrated.  New suppliers are dismissed as incompetent. 


Once enthusiastic new suppliers are thanked either for succeeding in cracking the code or for their time and efforts if they have failed.  In over 90 % of cases, they are told the information will be held in abeyance if there is a real impetus to find a PVC substitute.

Read More

Topics: PVC, PVC free, phthalates

Timing is crucial to biodegradable plastics

Posted by Joel Longstreth on Tue, Sep 17, 2013 @ 04:31 PM

20130917 163658 Our 4 year oxobiodegradable bag is breaking down.  The reusable bag we made from plain LDPE while George H W Bush was president is still going strong.

The folks at told us they didn't like the concept of a biodegradable reusable bag; they were more into "lifetime" bags.  

The contrast of the two projects was interesting.  The Makro bag was "outside in" thinking, or responding to a need.  The biodegradable bag was my "inside out " concept and while functional, a commercial dud.  I learned a lot, though.  Mainly how much visceral hatred there is for plastics, even if biodegradable ( " you're still usin' evil fossil fuels, MAN ! ).   I found it amusing these same people like their woven polypropylene reusable bags printed with heavy metals for the conspicuous consumption billboard.  

20130917 172812

How times have changed.  I went to the Whole Foods flagship store in Austin a few weeks ago and was denied a plastic shopping bag.  Nobody sees the irony of what must be millions of pounds of plastic that pass through Whole Foods every year in packaging.

At long last the FTC is going after biodegradable additive manufacturers who have specious claims.  The central issue ?  timing


Read More

Topics: biodegradable plastics

Clear Polyethylene Film

Posted by Joel Longstreth on Fri, Jun 07, 2013 @ 03:52 PM


20140128 130126

The not subjective definition of LDPE film clarity is ASTM D 1003 which measures haze.  Haze is a measure of how much light gets through plastic film measured in percent.  There is an inverse correlation between the haze number and clarity of plastic film.  The lower the number, the more light gets through.

While a low haze film allows the consumer to see the product at point-of-sale, the amount of attention paid to the difference between a few points of haze is overdone.  Many PE film extruders tout their runway versions of clear film as the only film the discerning customer will pick up. Seriously ? 

What is often overlooked is the difference between haze and what is known as contact clarity.  In the above pic, note how the film appears clearer where it is in contact with the image underneath.

Someday I would like to meet the mystery shopper who does not buy bread, nuts and bolts, candy, carrots, paper towels or bottled water because the haze is 12 instead of 6.

Read More

Topics: LDPE film, clear PE film, polyethylene film, PE film haze

Poly Film Thickness vs. Poly Film Yield

Posted by Joel Longstreth on Wed, Feb 20, 2013 @ 03:25 PM


Point-to-point variation is different than the area derived from a specific amount ( weight ) of PE film.  The word for total amount derived is called yield.


The industry standard is loosely defined as plus /  minus 10 %.  Smaller custom orders should allow wider tolerances.


Here's what happens in real life:  The operator sets up the order.  When the conditions of width, resin recipe and polyethylene film thickness ( a tad on the thick side ) are right, the first roll(s) of custom saleable film is started. The target weight of the first roll of layflat tubing or first two rolls in the case of single wound sheeting will be "heavy" or over the target weight.  Adjustments to the process conditions are then made.  By the third roll of layflat tubing or "set" of sheeting, the roll weights will be lighter than the target weight thereby ensuring good yield. 

Over the course of the run, the customer will get more area than what is referred to as the " theoretical" yield. Theoretical yield is calculated by dividing the yield, or weight per 1,000 lineal feet, into the total pounds shipped. Example:  35" X 4 mil sheeting weighs 56 pounds per 1,000 lineal feet ( the "yield" = 56 pounds ).  If 3,158 pounds are shipped, the theoretical yield, or number of feet the customer should have gotten out of 3,158 pounds is 56,392.

What also happens in real life:  If someone on the line in a printing / converting shop runs excess scrap, the tendency is to blame the film.  The excuse is the extruder shipped "heavy", or film thicker than ordered.  Carefully selected samples from the scrap bin are offered as evidence.  Samples are of course from the extruder's setup rolls.  The invoice is paid short and the dispute argument begins.

Two other common scenarios are failures resulting from gauge chiseling by either or both distributors or bagmakers.  For custom bags:

1.  Customer orders bags or film of a specific thickness.  
2.  Distributor shops it with RFQ of 10% lighter than the gauge called out
3.  bagmaker quotes shaving another 10% or more
4.  when the film order goes to the extruder's shop floor, the operator has + - 10% leeway so right there the film could be 30% light.
5.  the bags fail 
6.  the acrimony begins

For rollstock:

Distributors sell film by the roll with the ostensible gauge on the tags taking advantage of the information asymetry.  Plant managers have enough to deal with.  They trust their distributor and have no idea how to keep them honest.
Film is ordered light of course.

Because we do not engage in this common practice we do not do business with many distributors.  Our orders show the same information to the customer and to the shop floor.

Read More

Topics: poly film, polyethylene plastic film, LDPE film properties', poly film thickness

Barrier Films depends on the context

Posted by Joel Longstreth on Fri, Sep 07, 2012 @ 01:12 PM

dreamstime xs 25468564

Barrier films and barrier packaging definitions are all relative.

The term "barrier" is often used loosely ranging from a moisture vapor barrier in construction, barrier to bodily fluids in surgical drapes or fluid collection, controlled permeability in fresh cut packaging to measuing the amount of oxyen which passes across 100 square inches in 24 hours in terms of a few hundreds of a cubic centimeter.

When describing a barrier to your film supplier, it is important to know where you what degree of vacuum you need.  Oxygen Transmission Rate, or OTR is the most common benchmark.  Moisture Vapor Transmission Rate is MVTR for short.  CO2TR is not often referenced, but it means Carbon Dioxide Transmission Rate.   The ratios between these are difficult to manipulate; this poses restrictions on design.  I stopped testing for CO2TR over 16 years ago when i noticed a constant ratio of about 4:1 between carbon dioxide (4) and oxygen ( 1 ) permeability.  This is counterintuitive because the CO2 molecule is much larger than the oxygen molecule, right ?  Turns out CO2 is more combinable than oxygen ( remember high school chemistry and valences ? ).   MVTR depends on the solubility of resins selected.  Nylon and EVA are water soluble and provide pathways to conduct H20.  An example of practical application - I used to add EVA to lettuce film to wick out excess moisture and minimize micro loads.

For an extreme barrier usually for meat packaging, the traditional test method is ASTM D 3984.  This method measures a sample about the size of a thumbnail and interpolates to 100 square inches in 24 hours at specified relative humidity and temperature ( after 24 hours of conditioning, of course ). In the 1990's a test method for higher permeability films was needed for cut vegetable packaging.  The specimen size is larger.  For more information, contact MOCON or Illinois Instruments.

To achieve these low values which are expressed as maximum of 0.06 for example, there are two avenues:

EVOH; short for Ethylene Vinyl Alcohol
EVOH must always be coextruded in the core layer of a coextrusion


polyvinyl dichloride PVDC, a/k/a Saranex which can be coated on to substrates such as nylon, polypropylene and PET.

Either one of these structures have the same barrier film properties when laminated to a polyethylene sealant layer.

In the 1990's, the advent of fresh-cut produce demanded an entirely new way to measure precision controlled permeability films.  Fresh-cut produce needs relatively poor barriers to allow the vegetable to continue to respire.  A barrier film will rapidly induce unacceptable anaerobic conditions.  The balancing act is matching the permeability of the film to the metabolic rate of the vegetable. 

Measuring relatively high permeability rates requires a larger sampling size which cannot be accurately interpolated with a tiny sample size.

There are two applications which do not need barrier films yet continue spec out barrier films for a security blanket factor are:

Frozen food
Barrier films will not prevent freezer burn or prolong shelf life.  Take it on faith.

Vacuum packaging of inert things like tools, foam and kits.  If the item being packaged is inert, there is no concentration gradient or reason for nature to seek equlibrium.


note about the relationship between permeability and thickness in polyethylene:

Whether you measure by OTR or CO2TR, the permeance as it relates to thickness is not a linear relationship.  Under two mils the OTR increases dramaticaly; over two mils it flattens out slowly.

Read More

Topics: PVDC, moisture barrier, EVOH, barrier film, saran, oxygen barrier

BPA free is irrelevant to most plastics

Posted by Joel Longstreth on Thu, Sep 06, 2012 @ 10:25 AM

The truth about the hysteria over whether the BPA residue is real or contrived is up for grabs.  Manufacturers and retailers of canned goods are under tremendous pressure to prove their cans do not contain BPA residue even in the absence of a viable alternative.  


We are not going to take sides.  Polyethylene and other commodity polymers have an airtight alibi - they are nowhere near the scene of the manufacture of polymers made with BPA as part of the process.

If you don't already know: bisphenol A, or BPA for short, is a precursor / catalyst to make some polymers such as PVC, polycarbonate and mostly epoxy.  Like any catalyst, it is mostly transformed in the reaction.  The controversy is over what levels of residue are toxic.

If it's really a problem, 5 gallon polycarbonate carboys should be banned if the threshold is zero.


Water bagged in polyethylene would have no BPA because BPA is not used in the production of commodity polymers.  According to a recent study by the US Food and Drug Administration,low-dose exposure to BPA did not result in adverse health effects.

For the full report on BPA in cans, click here.  For a webinar which discusses the study, go to  For questions, email ops@  One of the points they make is that the rush to find substitutes can lead to what they call "regrettable substitution."  PVC linings turned out to be worse than BPA - based epoxy.

We have written dozens of letters which certifiy that our polyethylene films do not contain BPA.  BPA is not a component of the production of polyethylene and many other plastics, so to us it's an absurd waste of time.  The recipients of the letters we write go to companies who probably have 5 gallon carboys in the office.  The carboys are made of polycarbonate which is BPA - derived and no doubt contains residual BPA which could leach into the water.  The person who files the letter is exposed daily to cash register receipts which expose them to dermal contact several times a day.

There is no harmonization of the assessment of the risks associated with BPA.  The NDRC wants a ban, the National Institute of Health has "some concern" while the EPA says BPA does not pose a health concern.  The FDA has reaffirmed the safety of BPA in can linings. France has banned BPA from canned food lining.

California has added BPA to the burgeoning list of prop 65 chemicals.  


Now you are ready to spot phony eco labels.  The common thread is "never had it / never will."

Eternal water touts their "biobottle" as BPA free and 100% recyclable - a shameless marketing spin.  



Warp's shelf liners made from polyethylene.



Cuisinart coffee maker
The original mid 1970's Mr. Coffee machines were BPA free polypropylene, too.  They really went out of their way to make the parts out of non BPA derived plastic, didn't they ?


update February 26, 2018

Bad news for the  NGO's today.  

Read More

Topics: BPA, bpa free bottles, bisphenol A, BPA free, bpa free plastic

LLDPE Linear Low Density Polyethylene varieties

Posted by Joel Longstreth on Thu, Jul 26, 2012 @ 03:08 PM

As with all polymers Linear Low Density Polyethylene LLDPE has a tremendous variation within the species.
This article explains the differences in context of the history and evolution of Linear Low Density PE.

Think of the differences between the grades like the difference in gasoline choices:

Butene    =   Economy                             Hexene   =    Mid grade                            Premium  =    Octene

These refer to the types of comonomer married up with the ethylene monomer to make linear low density polyethylene.

A quick history lesson might help.  Or watch this video.

Until the late 1970's, " linear" polyethylene was verbal shorthand for milk jug high density polyethylene HDPE.  It was nicknamed " linear " because it had very little short chain, or amorphous, branching.  The shape of the molecules was more like spaghetti before cooking vis a vis after cooking.

spaghettiraw                                      spaghettibaby

When Carbide shook the plastic world with the unveiling of their Unipol "gas phase" linear polyethylene in 1978, there was a lacuna, or " gap " in polyethylene lingo.  PE with density under 0.930 is by definition LOW density        ( LDPE ) polyethylene.  To distinguish this new Low Density Polyethylene LDPE from conventional LDPE, it was dubbed LINEAR low density polyethylene or LLDPE for short.

Dow had a different approach with their " solution " phase polymerization process.  This mimicked the old DuPont Canada SCLAIR LLDPE resin which was the true forerunner of all Linear Low resins.  ( Apparently references to Sclair are lost to history; references from the pre-digital age have not come down to us.  After an extensive search, we could not find any articles on the history of Sclair.  If you come across one, please forward it to us. )

Carbide opted for the cheaper butene and Dow went top shelf with octene.  In the 80's, Dow's was easier to process ( less susceptible to melt fracture ) and had better physical properties than the butene gas phase.  As a side note, Carbide tried for several years unsuccessfully to induce extruders to take the resin in the form of a powder ( think laundry detergent consistency ) and pass along the savings of pelletization.  Dow provided old fashioned pellets.

In the 90's, Mobil tried to bridge the gap with hexene which is less expensive than octene and more expensive than butene.  They made LDPE resins on Unipol style reactors.  They chased Octene with  " super " hexene which has always been " not exactly " octene.  The solution phase process allows more versatility and faster changeovers than Unipol.  

Skip ahead to today.  Butene - 1 is the only LLDPE film resin which is sold as a commodity on the London exchange.  It is cheap and weak.  Nova purchased the DuPont Canada PE resin works a few years ago.  Nova offers both butene and octene LLDPE.  "Super" hexene is still around.  Lower cost Unipol resin plants have sprung up all over the planet.  Nova just announced an expansion of another billion pounds of butene capacity.

The advent of the "swing" reactor, or a reactor which can make all densities has been a hot topic in the industry, it's probably too far in the weeds if you're joining the party late.  Suffice to say it makes rating a resin maker's capacity tough to call.

It's kind of amusing to look back at the predictions of the late 70's with the benefit of hindsight.  Everybody thought LLDPE would make LDPE obsolete like TV was going to be the nemesis of radio.

Blends of LDPE and LLDPE deliver some interesting properties.  

When specifying Linear Low LLDPE, be specific about which kind of LLDPE you want and whether you want it 100% or blended with one of the myriad varieties of conventional LDPE.  Or you could give the extruder the job description and leave the resin selection up to them. 


Read More

Topics: Linear Low Density Polyethylene, LLDPE

Plastics in-depth and insights


Plastic Blogs

Subscribe by Email

Most Popular Posts

Browse by Tag