Semi-crystalline feedstock for filament-based 3D printing of polymers

A polypropylene-based material has been formulated to be suitable for fused deposition modelling (FDM). In fact, the high volumetric shrinkage and the rheological behaviour are main problems whereby polypropylene (PP) is not commonly used as a 3D printing filament. Experimental results have evidenced how material modifications have a strong impact on rheological behaviour, providing critical features that permit and improve material printability. An optimised 20 wt% talc filled heterophasic PP copolymer has been developed. The peculiar properties of the materials have been assessed by thermal characterisation and rheological analysis. Several process parameters (extrusion temperature, screw speed, cooling conditions) have been evaluated in order to obtain a proper filament. Finally, a model part has been printed using different settings to check printing quality by morphological analysis.

Designing 3D printable polypropylene: Material and process optimisation through rheology

A SiO2/MgCl2-bisupported Ziegler–Natta-type catalyst is studied in gas-phase ethylene/1-butene copolymerization. With a minimal amount of alkylaluminum required to activate the catalyst, polymeriza...

/pdf/engineering-poly-ethylene-co-1-butene-through-modulating-the-21pjcnf2yo.pdf

Engineering Poly(ethylene- co -1-butene)through Modulating the Active Species by Alkylaluminum

Polyolefin-based thermoplastics such as polyethylene and polypropylene constitute a major fraction of the polymers employed in commodity applications due to their ease of processability, durability, and economic viability. Additive manufacturing (AM) of polyolefins offers both a viable path toward functional prototyping of design concepts and direct manufacturing of end-use parts. Melt-based AM of polyolefins is more challenging than other semicrystalline polymers (polyamides) due to the relatively high levels of volumetric shrinkage encountered during crystallization of such polymers that lead to significant issues related to warpage and interlayer adhesion. The focus of this review is to evaluate the latest state-of-the-art for processing polyolefins by powder bed fusion (PBF) and material extrusion (MatEx) AM modalities. Recent progress in processing neat, filled, and blends of polyolefins using PBF and MatEx are discussed to highlight the importance of the rheological and morphological characteristics of the polymer melt on the printed parts performance. The existing challenges to AM of polyolefins are emphasized and strategies to address the limitations are recommended through a better understanding of the associated process-structure-property relationships. A holistic approach spanning synthetic modifications for feedstock development, improved system design, and physics-guided process parameter selection is required to broadly adopt melt-based AM of polyolefins. 

Melt-Based Additive Manufacturing of Polyolefins Using Material Extrusion and Powder Bed Fusion

A massive carbon footprint is associated with the ubiquitous use of plastics and their afterlife. Greenhouse gas (GHG) emissions from plastics are rising and increasingly consuming the global “carbon budget”. It is, hence, paramount to implement an effective strategy to reclaim postconsumer plastic as feedstock for technologically innovative materials. Credible opportunity is offered by advances in materials chemistry and catalysis. Here, we demonstrate that by dynamically crosslinking thermoplastic polyolefins, commodity plastics can be upcycled into technically superior and economically competitive materials. A broadly applicable crosslinking strategy has been applied to polymers containing solely carbon–carbon and carbon–hydrogen bonds, initially by maleic anhydride functionalization, followed by epoxy–anhydride curing. These dynamic networks show a distinct rubber modulus above the melting transition. We demonstrate that sustainability and performance do not have to be mutually exclusive. The dynamic network can be extruded into a continuous filament to be in three-dimensional (3D) printing of complex objects, which retain the mechanical integrity of vitrimers. Being covalently crosslinked, these networks show a thermally triggered shape-memory response, with 90% recovery of a programmed shape. This study opens up the possibility of reclaiming recycled thermoplastics by imparting performance, sustainability, and technological advances to the reprocessed plastic.

https://pubs.acs.org/doi/pdf/10.1021/acsapm.2c00340

Fused Filament Fabrication of a Dynamically Crosslinked Network Derived from Commodity Thermoplastics

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mren.201900044

Polypropylene Copolymers Designed for Fused Filament Fabrication 3D-Printing

Chemical recycling of plastic waste has promise as a complementary technology to increase eco-efficiency of plastics life cycles. Accumulation of impurities in feed streams can affect sensitive compounds such as the Ziegler–Natta catalyst systems commonly used to produce polyolefins such as high density polyethylene (HDPE) and linear low density polyethylene (LLDPE). In a poison study, the influence of impurities—more specifically NO and N2O—on the catalyst system are investigated comprehensively in terms of kinetic behavior and activity rates. A product composition analysis gives insights into product properties such as molecular weight distribution (MWD), comonomer composition distribution (CCD), melting point, and crystallinity. By applying known modeling techniques (kinetic modeling, MWD, and CCD deconvolution modeling), information beyond analytical data is obtained. The results of the study show that both poisons significantly affect catalyst kinetics and reduce catalyst activity. N2O influences primarily the MWD, while NO poisoning strongly affects the CCD of LLDPE samples. Since the mechanical properties of the polymers produced depend on factors such as MWD and CCD, NO and N2O poisoning may reduce their processability and applicability. 

Nitrogen Poisoning of HDPE and LLDPE Based on Chemically Recycled Post‐consumer Plastic via a Kinetic and Microstructural Modeling Technique

From Simulation to Distribution: A Novel Approach to Depolymerization Kinetics Using PHB Hydrolysis as a Case Study

Extended Abstract Ziegler-Natta (ZN) catalysts are among the most significant types of catalyst for the industrial production of plastics. The main components of ZN catalysts are TiCl4 in combination with an organic aluminium component as a cocatalyst. In addition, there are a variety of chemicals that improve or alter the catalyst behaviour. Various carrier materials such as MgCl2 or SiO2 are used to influence catalyst activity and particle shape. In addition, there is a large group of electron donors for influencing the catalyst behaviour and the final polymer [1, 2]. Nevertheless, the aluminium compound as a so called “cocatalyst” is one of the most decisive factors in the polymerization with ZN catalyst systems [3]. Therefore, a systematic study was carried out to determine the influence of different aluminium alkyls on the homo-polymerization of ethylene with a ZN catalyst system. For the experiments triethylaluminium (TEA), triisobutylaluminium (TIBA) and tridodecylaluminium (TDDA) were used in different concentrations. The three components were selected for their different properties and industrial importance. TEA is the most commonly used aluminium alkyl with little to no steric hindrance. TIBA is a, more complex aluminium alkyl mainly used as scavenger agent, while TDDA is generally unknown. A 0.5 l multi-purpose reactor system with liquid propane as solvent and a commercially available ZN catalyst of the 4 th generation were used to carry out the polymerizations. The data obtained was used to model the polymerization activity based on kind and amount of the aluminium alkyl used. The polymerization activity was different for each aluminium alkyl. While the polymerization activity increased to a plateau for the more complex aluminium alkyls TIBA and TDDA, TEA behaved differently. With TEA as a cocatalyst, the polymerization activity increased to a peak value at a concentration of 3 mmol l -1 and decreased for higher concentrations. In general, the polymerization activity achieved, increased with the size of the aluminium alkyl molecule. TDDA exhibited the highest polymerization activity at 4.5 mmol l -1 , which was 25% above the activity level for TEA and 20%, respectively, over that of TIBA. In conclusion, the steric differences of the used aluminium compound have a great influence on the polymerization activity. Based on the experimental data, a model was created to simulate all cases for the concentration of the three different aluminium alkyls. For this, the model postulated by Alshaiban and Soares [4] was extended to additionally represent the influence of aluminium alkyl and its concentration.

/pdf/influence-of-different-aluminium-alkyls-on-the-ziegler-natta-3848pf2gl1.pdf

Influence of Different Aluminium Alkyls on the Ziegler-Natta Polymerization

Polyethylene is one of the most widely used polymers, and it can be found in various industrial applications. The annual production and consumption of polyethylene is currently higher than 100 million tons worldwide, or about 40% of the consumption of all thermoplastic materials [1].

Bimodal Polyethylene: Controlling Polymer Properties by Molecular Design

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