The Impact of Primary Sludge on the Physical Features of High-Density Polyethylene (HDPE) Composites

Kati Mustonen,Timo Kärki,Ville Lahtela

doi:10.3390/resources8040184

Kati Mustonen, Timo Kärki + Show 1 more

Open Access

https://doi.org/10.3390/resources8040184

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Abstract

The cost-efficient reutilization of byproduct materials is a significant global goal, contributing towards the sustainable use of resources. In this study, the effects of including primary sludge in composite materials on their physical performance are examined, in order to achieve more effective reuse. The studied materials were made from high-density polyethylene (HDPE), anhydride-grafted polyethylene (MAPE), lubricants, and either wood flour from spruce (Picea abies) or primary sludge from the side-stream of forest industry processes as a filler. The materials were compounded by agglomeration, followed by manufacturing with a conical twin-screw extruder. The physical properties of the materials were characterized by water absorption and thickness swelling tests; furthermore, impact strength was characterized after the stress of a cyclic freeze-thawing test. The elemental compositions of the materials were also analyzed by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Primary sludge, as a component in the structure of the composite material, resulted in a significant improvement of moisture behaviors in the water absorption and thickness swelling tests. The identified results demonstrate that primary sludge is a technically applicable material for utilization in composite materials.

Highlights

Industrial byproducts may serve as valuable raw materials in applications, and their utilization as raw materials can contribute, simultaneously, to the idea of a circular economy
An element analysis by SEM-EDS identified the elemental composition of the primary sludge (Pr-Sl)/high-density polyethylene (HDPE) materials, which are presented in Table 2 as an average value from three samples
We investigated the effects of including primary sludge on the physical properties of a HDPE composite, consisting of 50% HDPE and 44% primary sludge or wood flour, together with 3%

Summary

Introduction

Industrial byproducts may serve as valuable raw materials in applications, and their utilization as raw materials can contribute, simultaneously, to the idea of a circular economy. The utilization of byproducts reduces the exploitation of primary resources and waste disposal, while simultaneously creating economic growth. Primary sludge is the residual solid generated by effluent treatment. The effluent is mechanically processed (sedimentation, flotation, or filtration) to remove fibers and suspended solids. Solid matter is settled by gravity in a clarifier, generating the primary sludge. The effluent treatment process is further continued with a secondary treatment, where dissolved organic compounds are removed with biological methods. The most usual method is an activated sludge process, where microbes oxidize the organic matter into biomass, carbon dioxide, and water.

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