Laurens Delva

Mechanical and chemical recycling of solid plastic waste

This review presents a comprehensive description of the current pathways for recycling of polymers, via both mechanical and chemical recycling. The principles of these recycling pathways are framed against current-day industrial reality, by discussing predominant industrial technologies, design strategies and recycling examples of specific waste streams. Starting with an overview on types of solid plastic waste (SPW) and their origins, the manuscript continues with a discussion on the different valorisation options for SPW. The section on mechanical recycling contains an overview of current sorting technologies, specific challenges for mechanical recycling such as thermo-mechanical or lifetime degradation and the immiscibility of polymer blends. It also includes some industrial examples such as polyethylene terephthalate (PET) recycling, and SPW from post-consumer packaging, end-of-life vehicles or electr(on)ic devices. A separate section is dedicated to the relationship between design and recycling, emphasizing the role of concepts such as Design from Recycling. The section on chemical recycling collects a state-of-the-art on techniques such as chemolysis, pyrolysis, fluid catalytic cracking, hydrogen techniques and gasification. Additionally, this review discusses the main challenges (and some potential remedies) to these recycling strategies and ground them in the relevant polymer science, thus providing an academic angle as well as an applied one.

The Effect of Injection Molding Temperature on the Morphology and Mechanical Properties of PP/PET Blends and Microfibrillar Composites

Within this research the effect of injection molding temperature on polypropylene (PP)/poly(ethylene terephthalate) (PET) blends and microfibrillar composites was investigated. Injection molding blends (IMBs) and microfibrillar composites (MFCs) of PP/PET have been prepared in a weight ratio 70/30. The samples were processed at three different injection molding temperatures (Tim) (210, 230, 280 °C) and subjected to extensive characterization. The observations from the fracture surfaces of MFCs showed that PET fibers can be achieved by three step processing. The results indicated that Tim has a big influence on morphology of IMBs and MFCs. With increasing the Tim, distinctive variations in particle and fiber diameters were noticed. The differences in mechanical performances were obtained by flexural and impact tests. Establishing relationships between the processing parameters, properties, and morphology of composites is of key importance for the valorization of MFC polymers.

Blending of recycled mixed polyolefins with recycled polypropylene : effect on physical and mechanical properties

The similar densities of polyethylene (PE) and polypropylene (PP), complicate the separation for these materials in the mechanical recycling of post-consumer plastics. Therefore, recycled mixed polyolefins (rMPO) are widely available as recycled (r) polymer material. These blends are commonly cheaper, but also inferior in properties to relatively pure waste streams of rPP or rPE. In order to improve these materials, blends of rMPO were made with more expensive, relatively high quality rPP. This approach was purposefully ‘bottom up’, exploring how to upcycle the lower grade rMPO instead of downcycling higher grade rPP with a measure of added (cheaper) rMPO. Blends were made with two types of rMPO, the one a HDPE-PP blends from hard plastic waste and the other a LDPE-HDPE-PP blends, based mostly on foil materials. Each of these materials had one type of mechanical property in common with the high quality rPP, these being Young’s modulus and toughness respectively. Blends were made at different concentration...

Development of crystalline morphology and its relationship with mechanical properties of PP/PET microfibrillar composites containing POE and POE-g-MA

The main goal of this research is to study the development of crystalline morphology and compare it to various mechanical properties of microfibrillar composites (MFCs) based on polypropylene (PP) and poly(ethylene terephthalate) (PET), by adding a functional compatibilizer and a non-functional rubber in two different steps in the processing sequence. The MFCs were prepared at a weight ratio of 80/20 PP/PET by twin screw extrusion followed by cold drawing and injection moulding. The non-functionalized polyolefin-based elastomer (POE) and the functional compatibilizer (i.e., POE grafted with maleic anhydride (POE-g-MA)) were added in a fixed weight percentage at two stages: during extrusion or during injection moulding. The morphology observations showed differences in crystalline structure, and the PP spherulite size was reduced in all MFCs due to the presence of PET fibrils. Their relationship with the mechanical performances of the composite was studied by tensile and impact tests. Adding the functional compatibilizer during extrusions showed better mechanical properties compared to MFCs. Overall, a clear relationship was identified between processing, structure and properties.

Influence of twin-screw configuration on the mechanical and morphological properties of polypropylene-clay composites

The influence of eight different twin-screw configurations, mainly varying in arrangement of restrictive (negative) kneading elements, on the mechanical and morphological properties of composites of polypropylene (PP) reinforced with organic modified montmorillonite (MMT) and coupling agent polypropylene-grafted-maleic anhydride (PP-g-MA) was studied. Pressure profile, maximum strain, fill rate and average viscosity were calculated using an existing twin-screw modelling software. Impact and tensile tests results, scanning electron microscopy (SEM) images and X-ray diffraction (XRD) measurements of the composites showed no significant influence of the position of the negative kneading blocks.

Long-term stability of cellulose acetate butyrate thin films for nuclear certified reference materials

Characterization of cellulose acetate butyrate (CAB) thin films with 17, 35 and 52 wt% butyryl is carried out to select the most suitable matrix material for the U and Pu containing large-sized dried spike reference material. The virgin CAB samples were aged by vibrations, heat, humidity, UV light and X-rays. Characterization was done by thermo-analytical techniques, gel permeation chromatography, mechanical tests and via Rayleigh and Compton scattering. The results show that CAB with lower butyryl content can withstand higher operational temperatures and has greater mechanical strength while CAB with higher butyryl content seems to be more resistant to radiation.

The upcycling of post-industrial PP/PET waste streams through in-situ microfibrillar preparation

Post-industrial plastic waste streams can be re-used as secondary material streams for polymer processing by extrusion or injection moulding. One of the major commercially available waste stream contains polypropylene (PP) contaminated with polyesters (mostly polyethylene tereftalate - PET). An important practical hurdle for the direct implementation of this waste stream is the immiscibility of PP and PET in the melt, which leads to segregation within the polymer structure and adversely affects the reproducibility and mechanical properties of the manufactured parts. It has been indicated in literature that the creation of PET microfibrils in the PP matrix could undo these drawbacks and upcycle the PP/PET combination. Within the current research, a commercially available virgin PP/PET was evaluated for the microfibrillar preparation. The mechanical (tensile and impact) properties, thermal properties and morphology of the composites were characterized at different stages of the microfibrillar preparation.

On the role of flame retardants in mechanical recycling of solid plastic waste

Flame retardants are used in a wide range of plastics to extend the time-of-escape from fires. By definition, they are designed to perform this task only in case of a fire, which is then automatically the end of the plastics lifetime. However, not all flame retardant plastic products are eventually set on fire, which is why they are abundant in plastic waste, potentially interfering with the mechanical recycling systems in place. To date, there has been little information on the influence of flame retardant additives during the mechanical recycling of solid (thermo)plastic waste. This contribution provides a comprehensive overview of the state of the art concerning the mechanical recycling of flame retardants containing polymers and plastics. In a first part, this review discusses the effect of mechanical melt reprocessing on the flame retardant properties of different recycled thermoplastic polymers, addressing questions whether the flame retardant additives are still present and effective after recycling and whether they interfere with the mechanical recycling itself. Special attention is paid to Waste from Electrical and Electronic Equipment containing flame retardants. A second part of the review lists several upgrading strategies for common polymeric waste streams that consist of adding virgin flame retardants to recycled plastics with the purpose of bringing an additional value to the compound.

New Approach to Optimize Mechanical Properties of the Immiscible Polypropylene/Poly (Ethylene Terephthalate) Blend: Effect of Shish-Kebab and Core-Shell Structure

Improving the mechanical properties of immiscible PP/PET blend is of practical significance especially in the recycling process of multi-layered plastic solid waste. In this work, a multi-flow vibration injection molding technology (MFVIM) was hired to convert the crystalline morphology of the PP matrix from spherulite into shish-kebab. POE–g–MA was added as compatibilizer, and results showed that the compatibilization effect consisted in the formation of a core-shell structure by dispersing the POE–g–MA into the PP matrix to encapsulate the PET. It was found that the joint action of shish-kebab crystals and spherical core-shell structure enabled excellent mechanical performance with a balance of strength and toughness for samples containing 10 wt % PET and 4 wt % POE–g–MA, of which the yield strength and impact strengths were 50.87 MPa and 13.71 kJ/m2, respectively. This work demonstrates a new approach to optimize mechanical properties of immiscible PP/PET blends, which is very meaningful for the effective recycling of challenging plastic wastes.

The effect of extrusion reprocessing on the properties of montmorillonite filled polypropylene

Composites of polypropylene (PP) reinforced with organic modified montmorillonite (MMT) (4 wt%) and compatibilizer were subjected to 15 extrusion cycles and compared with extruded virgin PP and extruded PP-compatibilizer. The materials were characterized by melt flow index (MFI), tensile testing and X-ray diffraction (XRD). The results showed an improved intercalation of the MMT clay in the first few extrusions, thus improving the mechanical properties. Further extrusion lead to a decrease in elastic modulus, which was attributed to a reduction in matrix-filler interaction, most probably caused by organoclay degradation as shown by thermogravimetric analysis (TGA).