When is it worth using virgin or recycled resin? (Part 1)

I see many people insisting on the same mistake on both sides: some producing parts that should be made from new material using recycled, while others who could use recycled plastic remain spending money on unnecessary new material.

As I work with plastic raw material I will give some tips so that you (buyer) have a balance between cost and quality.

Some resins suffer greatly from recycling, they lose many properties and this prevents them from being used in some applications. Others do not lose much and are already considerable options to replace virgin resins. The table below gives a sense of this:

Recycled material Performance level when compared to virgin resin (using 100% recycled)
PE, PP 9 It is a great option especially if the part to be produced is black, loses very little in mechanical properties when recycled. The disadvantage is due to parts that need a more precise value of fluidity, because the recycling works with margins and not with exact value.
PS 4 The main characteristic of styrenics is to lose impact resistance after recycling. In the case of PS, which is naturally weak in this respect, it is not worth recycling it as PS unless it is being transformed into HIPS.
HIPS 7 Sometimes it may be necessary to increase the amount of impact modifier during recycling so it does not become brittle. It does not lose significant visual quality.
ABS 8 ABS is generally used in parts that require excellent visual appearance, and at this point the recycled one fails, in addition to a marked drop in impact resistance. It is a material that makes up for making a virgin / recycled blend since the price of the new resin is medium-high, so you have a good cost-benefit ratio. Here it is being classified as "8" because we are talking about 100% recycled resins, and at this point the price difference for ABS is great.
POM 9 Even when 100% recycled is a material that does not give problem related to mechanical properties.
Polyamides (Nylon, PA6 and 6.6) 8 The situation of the polyamides is very similar to the one of the ABS, with the difference that the applications of the PA's do not aim at both the appearance but the mechanical resistance.

Problems related to brittle material, sneezes, and blemishes often caused by contamination during recycling may arise. Even so, the cost-effectiveness is attractive.

Label
0 - Poor performance against virgin resin
10 - Same performance as virgin resin

As you can see, in the table above I did not put any plastic in the polyester family (PBT, PET) because few companies recycle these materials and honestly I do not know the performance of these resins when recycled. The PC has a good cost-benefit (the new resin is expensive), but lack a larger study to know its behavior when recycled in more varied applications.

What I can say about polyesters is that even virgins are relatively "laborious" to process when compared to other plastics, I also notice a lot of PBT ground scrap kept for years in recyclers who are not interested in this material, PBT will absorb a lot of moisture, making recycling unfeasible.

Keep an eye on the supplier

There are recyclers of plastics from the most varied, from disorganized to well structured companies and with material of great quality, so the buyer must research well the supplier to have no future problems.

Some companies that recycle cheaper materials like PP, PE and PS do not invest in equipment, qualification of employees, and much less in quality control of the product.

I cite as example a polyethylene recycler I once visited, where they grabbed dirty sacks with powdered chemicals or other contaminations (metal, wood, paper) and simply threw these bags into a binder and then straight into the hopper of the extruder. There was no wash! The extruder screens clogged every 10 minutes of so much dirt it had on the material.

In the case of styrenics (PS, ABS, SAN) what happens is the contamination by plastics from the same family, which can make the material brittle. Ideally, recycling of these resins should be done by specialized companies that have professionals trained to perform scrap sorting and to separate primarily ABS from the PS, where it may be difficult to distinguish between one and the other case the person who carries out the sorting has no experience.

In the recycling of polyamides (nylons) there is a lot of mixing between 6 and 6.6, which to some extent is not harmful, but what should be noted is for the nylon fabric blend with nylon 6 or 6.6 for injection. Fabric nylon is exposed to soaps and other chemicals several times during its lifetime and when mixed with the injection materials it generates problems during processing.

Tissue nylon after granulation tends to "float" on the molding injection machine screw, meaning the machine cannot dose. One solution to this problem is to mix 5% polyamide 6.6 to this granulate, so that 6.6 because of the larger melting point sticks to the thread leaving it "rough", this will facilitate the dosing.

Continue reading this article:

2


Bibliography:
HARPER, Charles A.; PETRIE, Edward M. Plastics Materials and Process: A Concise Encyclopedia. Hoboken: John Wiley & Sons, Inc., 2003.
WIEBECK, Hélio; HARADA, Júlio. Plásticos de Engenharia: Tecnologia e Aplicações. São Paulo: Artliber Editora, 2005.
Article posted in May 25, 2017
About the author: Daniel Tietz Roda is Plastics Technologist graduated from the FATEC/ZL and Mechanical Design Technician from ETEC Aprígio Gonzaga, in São Paulo, Brazil. Roda worked 5 years with technical assistance and development of plastics in industries and nowadays is the publisher of this website.
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