Don’t dread those two EU rules spreading around the world. With just a bit of understanding, testing for the forbidden ingredients can be routine.
By now, almost everyone involved in the world of manufacturing has at least heard of the acronyms RoHS and REACH. Even if you have not, the chances are quite good that your organization is being affected by these initiatives in a manner that consumes time and resources.
ï»¿This series of articles is designed to help molders understand how a few analytical tools can help diagnose a part failure. Michael Sepe, our analyst and author, is an independent materials and processing consultant based in Sedona, AZ. Mike has provided analytical services to material suppliers, molders, and end users for 20-plus years. You can reach him at [email protected].
RoHS, or Regulation of Hazardous Substances, was the first attempt to formalize limitations on the use of materials often known as heavy metals. These include cadmium, lead, mercury, and hexavalent chromium. The current rules state that if any of these elements is present at a level in excess of 1000 ppm (0.10%) by weight in a particular component, then the component cannot be shipped to or sold in certain parts of the world. Some lists that are perhaps anticipating further regulation also add antimony, arsenic, barium, and selenium.
While the European Union gets most of the credit or blame (depending on how you look at it) for these rules, the reality is that their effect is extending around the world, as shown by the furor over the lead in toys coming from China to the United States last year. Because of that particular incident, U.S. legislation was passed and signed into law in August of this year that imposes additional responsibilities on manufacturers in certain markets to show that their products are free from specific substances, including lead and certain types of plasticizers known as phthalate esters.
Not all phthalate esters are banned, at least not yet. And that is part of the problem. The number of these lists of banned or proposed banned substances is increasing, they appear subject to frequent changes, and it seems that everyone has a different list. There is not even general agreement on the amount of each substance that will be allowed. The new U.S. law initially permits a level of 1000 ppm for the objectionable substances, but progressively reduces the amount over the subsequent two- to three-year period.
Returning to our RoHS list for a moment, an additional set of substances has been added and has reached the level of full enforcement as of July of this year. These are families of flame retardants known collectively as polybrominated biphenyls (PBB) and polybrominated diphenyl ethers (PBDE). So now there will be a lot of attention directed to the amount of bromine in a compound. But it is not all bromine, only bromine that is part of these banned compounds. The use of other brominated flame retardants is still permitted, at least for now.
Some of you may have received letters from material suppliers in the last few months delivering the bad news that compounds that you may have been molding for years can no longer be shipped to you because they employ these PBBs or PBDEs and a substitute material will need to be found or is being recommended.
Providing proof of compliance
One of the big unresolved debates pertains to the level of certainty that manufacturers of materials and products will need to provide in order to satisfy the various regulatory agencies that they comply with the standards. Many material suppliers have rushed to get letters out to their customers stating that their materials are RoHS compliant. If you read these letters carefully, they do not exactly represent ironclad assurance. Most of them essentially state that the manufacturer of the material does not knowingly include any substances that would result in the presence of the regulated compounds. However, they go on to say that they do not test for substances that they do not anticipate are present.
Polymer compounds are complicated formulations. While 95-98% of any given compound is essentially the polymer plus any required fillers such as glass fiber, there will also be additives, lubricants, colorants, and other ingredients that may be considered minor but can easily exceed 0.1% of a material. If the manufacturer of the compound is not vertically integrated all the way back to the oil well, the mine, or the glass plant, then everyone is dependent on the next entity up the supply chain to play by the rules.
If you are a trusting soul, you file the letter from your supplier with the rest of your certification documents and cross your fingers. But it is probable that those administering these programs will ask for analytical proof of the compliance statements. Ahead of that potential demand, many companies have identified a market advantage in being able to state that their products are RoHS compliant and are seeking to establish this fact to an analytical certainty.
So whether the initiative is proactive or reactive, one of the essential questions relates to how compliance can be proven economically. Ideally, we would some day develop little kits similar to the ones sold to users of spas and hot tubs. These provide a colorimetric determination of pH, alkalinity, and other properties of the water. You do not need to be a chemist to perform these tests. Unfortunately, the technology has not advanced to that point. However, there are screening tools that can be used to address many concerns regarding regulated substances without having to set aside a huge piece of the operating budget for testing.
Tools to use
One of the simplest techniques available today is X-ray fluorescence (XRF). This technique is based on the principle that each element produces a unique response when bombarded by X-rays. Bench-top instruments that stay in the lab can detect elements quantitatively down to fluorine (atomic number 9) and can “see” elements semiquantitatively down to boron and carbon (atomic numbers 5 and 6, respectively).
Minimum detection limits go into the tens of parts per million. Recently, portable units have come onto the market with similar resolution capabilities; however, the lightest element that they can detect is titanium (atomic number 22). Fortunately, all of the elements on our undesirable list are heavier than titanium, so the technique is useful and with the portable unit you can go to the site where the product is rather than bringing the product to the lab.
While XRF does not tell us everything, this technique provides the first line in the determination for RoHS compliance. The findings for substances like lead, cadmium, and mercury can be taken at face value. Chromium can be present in forms other than hexavalent. Trivalent chromium is not harmful and XRF will not distinguish between the two types. But if total chromium content falls below 1000 ppm, then there is no need to go any farther with the determination.
The same applies to bromine. XRF tells us how much elemental bromine is present in our compounds, but it provides no information about the substances in which it is contained. In the substances we are concerned about, bromine makes up between approximately 74% and 85% bromine by weight. Therefore, any amount of bromine below 740 ppm automatically means that there cannot be more than 1000 ppm of these compounds present in the material.
There are some limitations here. One of them is the minimum detection level. Some clients want the test to be sufficiently discerning so that the tested product can be sold as “lead free” or “heavy metal free.” This gets tricky, because while RoHS says that anything below 1000 ppm is acceptable (for now), that is not the same thing as saying that there is none of the constituent in the material.
One thing that analysts are confronted with is the question of when it is acceptable to say that a particular constituent is completely absent from a compound. As analytical tools improve, it is possible to make increasingly accurate measurements using tools that can detect smaller and smaller quantities. A proper analytical result will provide a minimum detection limit (MDL) for a given test and if nothing is detected the result should state there is less than the MDL in the substance rather than stating outright that the substance is free of the ingredient.
Some of the alternative methods can get down to much lower levels than are practical for X-ray fluorescence. Inductively coupled plasma (ICP) coupled with techniques such as mass spectroscopy (MS) or optical emission spectroscopy (OES) can detect many elements down to 1-2 ppm. Mercury can be detected by a method known as cold vapor atomic fluorescence spectroscopy (CVAFS) down to levels of 1 ppb.
These methods are also important when a sample is not homogeneous. For example, a fabric that may be made up of more than one type of fiber and that may also contain a polymeric binder may present problems for XRF, but can be evaluated readily by these alternative methods. The good news is that as analytical techniques for polymers go, these methods, as scary as they may sound, are all quite reasonable in cost.
More costly analysis
REACH stands for Registration Evaluation Authorization & Restriction of Chemicals. It represents a longer list of 16 materials that are actually chemicals. While this list has not yet been solidified, one of the most recent incarnations is shown in the table. These chemicals are also slated for elimination from materials used to manufacture products, including plastic materials.
This list is obviously more complicated, and to perform all the tests necessary to detect and quantify everything on this list involves bringing out the big guns in terms of costs. However, even here an initial screening by XRF can be helpful. Four of these substances contain arsenic while sodium, chromium, cobalt, chlorine, bromine, and tin are part of five more. Therefore, more than half of the list can be ruled out or slated for further tests using one simple screening technique.
No one pretends that this is going to be an easy process. Just as we get a handle on each new wave of banned or regulated substances, organizations are hard at work proposing new and longer lists. The current REACH list started out as a much more extensive list that included substances like bisphenol A, the monomer used to produce polycarbonate.
The issue is not dead, only postponed. But as we go forward into this new territory, it will be important to balance the need for compliance that allows us to do business with the rest of the world with reasonable costs. While it cannot do everything, elemental screening is one of the front line tools that will help in this effort.
ï»¿A recent REACH list
Bis(tributyltin) oxide (TBTO)
Benzylbutyl phthalate (BBP)
Short chain chlorinated paraffins
Di(2-ethylhexyl) phthalate (DEHP)
Lead hydrogen arsenate
Dibutyl phthalate (DBP)