What Is Plastic Density & Why It Matters in Recycling

What is Plastic Density?

Density of a material in technical terms is the weight of the material (m)/volume of the material (V). This is normally expressed in grams per cubic centimeter (g/cm 3) in the plastics industry. Due to the fact that all polymers are constructed of varying molecular chains some tightly packed and others branched, they all have a distinct all plastic material density profile.

When we refer to the density of plastic, we are actually referring to the amount of stuff that is crowded in to a certain space. Indicatively, Polypropylene (PP) has been identified to be among the lightest plastic whereas Polyvinyl Chloride (PVC) weighs much more because it contains chlorine atoms. It is this core difference that can enable a recycler to apply very simple tank of water to extract the two.

Importance of Plastic Density

In recycling, the plastic density is the most important measure that can be applied to prove the quality and purity of a given material stream. In the absence of proper plastic material density chart and date, the recycling process would be full of mistakes resulting in downcycling or landfilling of good resources.

The significance of plastic density can be subdivided into some main areas:

Material Identification

It offers an infallible method of identification of the resin type in case there is no label, or the label becomes illegible.

Contamination Control

It makes sure that sinker plastics (such as PET) are not contaminated with floater ones (such as PE), otherwise it would lead to failure in the remaining manufacturing process.

Sorting Efficiency

Recycling processes are possible at a high-speed plastic density and thousands of kilograms per hour can be processed with minimum human effort.

Structural Integrity

To manufacturers, the mass, intensity and thickness of the new wall of any new packaging is directly related to the density of the received PCR resin.

All Plastic Material Density Chart

Engineers use a complete plastic material density chart to calibrate their machines in order to cope with waste streams. These values are the standard range of virgin resins but additives and fillers may slightly change these values.

Any facility that is interested in producing high-purity output must use a plastic material density chart. The table below provides an overview of the most widespread polymers and their behavior when used in a basic water-based separation system:

This plastic density chart on the density of plastic material underscores the reasons why water is a very good sorting medium. Plastics such as PP and HDPE will naturally rise on the surface whereas PET and PVC will sink to be separated mechanically in a clean way. The initial step in designing a reliable recovery line is the knowing of all the plastic material density values through a plastic density chart.

How to Calculate Density of Plastic

As a quality control, it may be required to test a load of material on site. Density of plastic is one of the standard requirements of lab technicians in recycling industries along with the help of a plastic density chart.

The most frequent one is the Displacement Method (which is based on the Archimedean Principle):

1. Measure Mass: The dry plastic sample must be massed using a precision scale to obtain $m.
2. Measure Volume: Place the sample in a graduated cylinder whose volume is known to contain a given volume of water. The alteration in water level is the volume of plastic denoted by V.
3. Find Formula: The result is obtained by applying the formula: $\rho = \frac{m/ V.

Density of plastic is crucial to learn how to make decisions that will determine whether it has heavy fillers or a lot of moisture that could have been absorbed during the waste collection stage.

Why Density Based Plastic Sorting Matters in Recycling

Recycling by the use of plastic density is seen most in the Float-Sink tank. This is a huge industrial vat in which flakes of plastic are shredded and swirled in water. Since the density of the plastic material, which is to be recycled, is so different in the bottle bodies (PET) compared to that of the bottle caps (HDPE), the bodies naturally separate in the tank.

This is done so that the PET flakes reaching the extruder would not be contaminated with polyolefins since this would form weak points of the new bottle. The use of these physical laws will guarantee that the resulting PCR will be consistent to be reused in the high demand FMCG packaging.

Impact of Density on Recycling Process

Plastic density in recycling may occasionally have slightly different density than virgin plastic because of the presence of inks, adhesives or multiple heat cycles, which interfere with and modify crystallinity of the polymer. The quality assurance at Banyan Nation includes monitoring of the plastic density in recycling.

In case the concentration of a batch of rHDPE is excessive it can tell that the material has mineral fillers or contains PVC. On the other hand, decreased density could indicate pinacolone between the polymer chains or foaming of the polymer. It is the consistency in the density of recycled plastic that enables our partners to replace virgin resin by our Better Plastic 2018 without re-engineering their complete production line.

Conclusion

Recycling is just a separation game, and the game rules are the plastic density. Since we start sorting on the MRF and continue to sort on our lab, it is the knowledge of the all plastic material density that helps us transform a mountain of mixed materials to a stream of usable resources. Through the strictest plastic density chart and advanced sorting technologies, we overcome the border between what is considered as waste and what is considered as commodity. With the future of 2026 and beyond in sight, the accuracy of density-based sorting will even be more of a necessity as we attempt to seal the loop on any of the most complex flexible packaging and rigid packaging.