Summary

The Effect of Construction and Demolition Waste Plastic Fractions on Wood-Polymer Composite Properties

Published: June 07, 2020
doi:

Summary

Secondary material streams have been shown to include potential raw materials for production. Presented here is a protocol in which CDW-plastic waste as a raw material is identified, followed by various processing steps (agglomeration, extrusion). As a result, a composite material was produced, and mechanical properties were analyzed.

Abstract

Construction and demolition waste (CDW), including valuable materials such as plastics, have a remarkable influence on the waste sector. In order for plastic materials to be re-utilized, they must be identified and separated according to their polymer composition. In this study, the identification of these materials was performed using near-infrared spectroscopy (NIR), which identified material based on their physical-chemical properties. Advantages of the NIR method are a low environmental impact and rapid measurement (within a few seconds) in the spectral range of 1600-2400 nm without special sample preparation. Limitations include its inability to analyze dark materials. The identified polymers were utilized as a component for wood-polymer composite (WPC) that consists of a polymer matrix, low cost fillers, and additives. The components were first compounded with an agglomeration apparatus, followed by production by extrusion. In the agglomeration process, the aim was to compound all materials to produce uniformly distributed and granulated materials as pellets. During the agglomeration process, the polymer (matrix) was melted and fillers and other additives were then mixed into the melted polymer, being ready for the extrusion process. In the extrusion method, heat and shear forces were applied to a material within the barrel of a conical counter-rotating twin-screw type extruder, which reduces the risk of burning the materials and lower shear mixing. The heated and sheared mixture was then conveyed through a die to give the product the desired shape. The above-described protocol proved the potential for re-utilization of CDW materials. Functional properties must be verified according to the standardized tests, such as flexural, tensile, and impact strength tests for the material.

Introduction

Global waste generation has grown significantly throughout history and is predicted to increase by tens of percentages in the future unless action is taken1. In particular, high-income countries have generated more than one-third of the world’s waste although they account for only 16% of the global population1. The construction sector is a significant producer of this waste due to rapid urbanization and population growth. According to estimates, approximately one-third of global solid waste is formed by construction and demolition projects; however, exact values from different areas are missing2. In the European Union (EU), the amount of construction and demolition waste (CDW) is approximately 25%–30% of total waste generation3, and includes valuable and significant secondary raw materials, like plastic. Without organized collection and management, plastic may contaminate and adversely influence ecosystems. In 2016, 242 million tons of plastic waste were generated in the world1. The share of plastic recycled in Europe was only 31.1%4.

Resource scarcity has created a need to change practices toward a circular economy, in which the aims are to use waste as a source of secondary resources and recover waste for reuse. Economic growth and minimized environmental impacts will be created by the circular economy, which is a popular concept in Europe. The European Commission adopted a European Union Action Plan for a circular economy, which set goals and indicators for contributions5.

Tighter environmental regulations and laws are contributing to the construction sector putting more effort into waste management and material recycling issues. For example, the European Union (EU) has set targets for material recovery. From the year 2020 onwards, the material recovery rate of non-hazardous CDW should be 70%6. The composition of CDW may vary widely across geographical locations but some common characteristics can be identified, including, for example, plastic that is a potential and valuable raw material for wood-polymer composites. The reutilization of plastic is a concrete step towards a circular economy in which virgin plastic polymers are substituted by recycled polymer.

Composite materials are a multi-phase system, consisting of a matrix material and reinforcing phase. Wood-polymer composite (WPC) typically contains polymers as the matrix, wood materials as reinforcement, and additives for improving adhesion, such as coupling agents and lubricants. WPC can be known as an environmentally friendly material because the raw material can be sourced from renewable materials, such as polylactic acid (PLA) and wood. According to the latest innovation7, the additives of WPC can be based on renewable sources. Additionally, the source of the raw material can be recycled (non-virgin) materials, which is an ecologically and technically superior alternative8. For example, researchers have studied extruded WPC that contains CDW, and found that the properties of CDW–based composites were at an acceptable level9. Utilization of recycled raw materials as a component for WPC is also acceptable from the environmental aspect, as proved by several assessments. Overall, it has been demonstrated that utilizing CDW in WPC production can decrease the environmental influences of CDW management10. In addition, it has been found that using recycled polypropylene (PP) plastic in WPC has the potential to reduce global warming11.

The amount of available recycled polymers will increase in the future. Global plastic production has increased approximately 9% as per year, on average, and it is expected that this increment will continue in the future12. The most general plastic polymer types are, inter alia, polypropylene (PP) and polyethylene (PE). The shares of total demand for PE and PP were 29.8% and 19.3%, respectively, in Europe in 20174. The global plastic recycling market is expected to grow at an annual growth rate of 5.6% during the period 2018–202613. One of the main applications in which plastics is used is building and construction. For example, almost 20% of the total demand for European plastic was associated with building and construction applications4. From an economic perspective, the use of recycled polymers in WPC manufacturing is an interesting alternative, leading to the production of materials with low cost. Previous research has shown that physical effects have a stronger influence on extruded materials made from secondary plastic compared to the corresponding virgin material, but properties depend on the plastic source14. However, the use of recycled plastic decreases the strength of WPC due to lower compatibility15. Variation between the structures of plastic polymers causes concerns for re-use and recycling, which contribute to the importance of plastic sorting based on the polymer.

This study intends to assess the utilization of plastic material from CDW as a raw material for WPC. The polymer fractions assessed in the study are acrylonitrile butadiene styrene (ABS), polypropylene (PP), and polyethylene (PE). These are known as universal plastic fractions within CDW. The polymer fractions are treated with general manufacturing processes, such as agglomeration and extrusion, and are tested with universal mechanical property tests. The primary objective of the study is to discover how the properties of WPC would alter if recycled polymers were used as a raw material in matrix instead of primary virgin polymers.

Based on the (local) waste management center (Etelä-Karjalan Jätehuolto Oy), it was shown how plastic-rich CDW is stored. It was demonstrated that a great amount plastic material is included and some examples of CDW plastic polymers were shown. Researchers collected the most suitable polymers for further processing, such as ABS, PP, and PE. The desired polymers (PE, PP, ABS) were identified using portable near infrared (NIR) spectroscopy. WPC product examples were presented in which where collected plastic materials could be utilized as a raw material. The definition of the composite and its advantages were explained.

Protocol

1. Identification and pre-treatment Identify polymers in plastic with the portable near-infrared (NIR) spectroscopy tool in the spectral range of 1600–2400 nm. Contact the polymer with spectroscopy tool and determine the polymer by the measured reflectance. According to the identification curve of spectroscopy, analyze the identification results from the screen in the laboratory. Based on the identification result, sort materials between the polymers and measure their…

Representative Results

To investigate the effect of CDW plastic polymer on the mechanical properties of WPC, three different polymer types as a matrix were studied. Table 1 presents the composition of materials and Table 2 reports the manufacturing processes. The material of CDW-PP requires a higher treatment temperature for tools but, correspondingly, melt pressure was lower compared to the other materials (CDW-ABS and CDW-PE). Figure 1 presents the fl…

Discussion

The mechanical properties of WPC play an important role in deciding the suitability of these products in various applications. WPC consists of three main ingredients: plastic, wood, and additives. The mechanical properties of fiber-based composites depend on the length of the used fiber, where “critical fiber length” is the term used to indicate sufficient reinforcement25. In addition to the properties of ingredients, the quality of raw materials is the important factor for the perform…

Disclosures

The authors have nothing to disclose.

Acknowledgements

The authors acknowledge the support of the LUT RESOURCE (Resource efficient production processes and value chains) research platform coordinated by LUT University and the by the Life IP on waste—Towards a circular economy in Finland (LIFE-IP CIRCWASTE-FINLAND) project (LIFE 15 IPE FI 004). Funding for the project was received from the EU Life Integrated program, companies, and cities.

Materials

Agglomeration Plasmec TRL100/FV/W apparatus of turbomixer
Agglomeration Plasmec RFV 200 apparatus of cooler
CNC router Recontech F2 – 1325 C CNC machine
Condition chamber Memmert HPP260 constant climate chamber
Coupling agent DuPont Fusabond E226 commercial coupling agent additive
Crusher 1 (crusher/shredder ) Untha Untha LR 630 10-20 mm sieve
Crusher 2 (low-speed crusher) Shini Shini SG-1635N-CE 5 mm sieve, granulator
Extruder Weber Weber CE 7.2 conical counter-rotating twin-screw
Lubricant Struktol TPW 113 commercial lubricant additive
NIR spectroscopy Thermo Fisher Scientific Thermo Scientific microPHAZIR PC
Recycled material ABS from CDW
Recycled material PE from CDW
Recycled material PP from CDW
Sliding table saw Altendorf F-90 circular saw/sliding table saw
Testing apparatus Zwick 5102 impact tester
Testing machine Zwick Roell Z020 allround-line materials testing machine
Wood flour (Spruce) material
WPC example material UPM Profi Decking board

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Cite This Article
Lahtela, V., Hyvärinen, M., Kärki, T. The Effect of Construction and Demolition Waste Plastic Fractions on Wood-Polymer Composite Properties. J. Vis. Exp. (160), e61064, doi:10.3791/61064 (2020).

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