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A good example is colorants. Has the supplier obtained a color sample before matching, and has it specified the type of light (fluorescent, LED, direct sunlight, etc.)? If gloss is important, is there a specification and at what angle? If it is transparent, remember that transmittance and haze are not exactly the same (see ASTM D-1003).

All of this has a political "angle." Some processors formulate their own compounds and know the amount of each additive. It’s understandable that other people buy formula compounds and their suppliers don’t want you to know exactly the ingredients. However, the buyer may need to know what's in it and how much (and sometimes nothing) to make sure that his product is suitable for food packaging, or does not violate California's infamous Proposition 65, or does not put the worker in any danger. If you don’t know what’s in it, and don’t need or don’t want to pay for laboratory analysis, at least write down the performance specifications on the compound you buy, such as the tensile strength/elongation/modulus of your product, or the compound Standard products made (note the use of injection molded samples for extruded products).

Identifying ingredients can also be a problem. Calcium carbonate (usually abbreviated as "calcium") is my favorite example because its influence depends largely on the particle shape and size, surface treatment and source purity. It is not enough to say that a compound "contains 15% calcium". The wood flour in WPC composites is even more confusing. Some things that need to be understood and understood are: long fiber and short fiber, hardwood and softwood, and particle shape and size, as well as the above-mentioned chemical treatment of calcium.

Mixing is also critical. One of my early awakenings was the late paper extruder and the ANTEC paper from George Kovach, the former president of SPE, who showed that better dispersion (smaller particles) means less colorant, which reduces costs. When I used the carbon-HDPE conductive formula, I learned later lessons, where too much mixing separates and encapsulates the carbon particles and requires more carbon black, which leads to higher costs and negative performance changes.

The smaller the percentage of additives, the more reasonable it is to use concentrates, because it is difficult to evenly distribute 0.25% of additives! Sometimes, the money spent on continuous feeders of pure additives or concentrates can be justified by requiring fewer additives to ensure proper performance. Examples of these microadditives include ultraviolet absorbers, anti-fracture processing aids, antioxidants, PET chain extenders, and many pigments and dyes.

In the concentrate, don't forget the resin carrier. A 10% load in one carrier may be very different from the same load in another carrier. Generally, the viscosity of the concentrate and the base resin mixed with it (at the extrusion temperature and shear rate) should be proportional to the ratio.

If you know your compound well, you can be more confident in its performance. I used to be an expert witness in a legal case in which the thermal stability of resin was questioned. We found that the supplier reduced the antioxidant level from 0.5% to 0.3% without telling the buyer, but this did not solve the problem because we still have to prove that 0.3% is too little for the application. This in turn depends on the antioxidant used, and the time-temperature history of the material-its time and temperature in the extruder. Even the extruder screen has a problem: if the resin degrades faster due to insufficient antioxidants, the finer screen may capture smaller degraded particles, which will promote product failure (stress concentration)器).

In legal cases, sometimes just such a discovery is enough to scare one party or the other to settle out of court, just like almost all cases I am familiar with. Please see the links to two of my articles on "Why do they call us witnesses?" On the homepage of my website.

Finally, I leave you with my favorite proverb: optimists say the cup is half full, pessimists say it is half empty... But the engineer/scientist/realist asks: how much is in the cup?

Allan Griff is a senior extrusion engineer. He initially provided technical services for a major resin supplier. Now he has been working independently for many years as a consultant and an expert witness in legal cases, especially as an educator and public and public educator through webinars and seminars. internal. As early as the 1960s, he wrote the first practical extrusion book and the plastic extrusion operation manual updated almost every year, and it is available in Spanish, French and English. Learn more on his website www.griffex.com or send an email to [email protected].

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