Thermal Conductivity of Polymer-Based Composites: Fundamentals and Applications

Purpose – The purpose of this paper is to systematically and critically review the literature related to process design and modeling of fused deposition modeling (FDM) and similar extrusion-based additive manufacturing (AM) or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature focusing on process design and mathematical process modeling was carried out. Findings – FDM and similar processes are among the most widely used rapid prototyping processes with growing application in finished part manufacturing. Key elements of the typical processes, including the material feed mechanism, liquefier and print nozzle; the build surface and environment; and approaches to part finishing are described. Approaches to estimating the motor torque and power required to achieve a desired filament feed rate are presented. Models of required heat flux, shear on the melt and pressure drop in the liquefier are reviewed. On leaving the print nozzle, die swelling and bead cooling are ...

https://forums.reprap.org/file.php?1,file=42240,filename=A_review_of_melt_extrusion_additive_manufacturing_processes_Process_design_and_modeling.pdf

A review of melt extrusion additive manufacturing processes: I. Process design and modeling

Theoretical prediction of effective properties for multiphase material systems is very important not only to analysis and optimization of material performance, but also to new material designs. This review first examines the issues, difficulties and challenges in prediction of material behaviors by summarizing and critiquing the existing major analytical approaches dealing with material property modeling. The focus then shifts to some recent advances in numerical methodology that are able to predict more accurately and efficiently the effective physical properties of multiphase materials with complex internal microstructures. A random generation-growth algorithm is highlighted for reproducing multiphase microstructures, statistically equivalent to the actual systems, based on the geometrical and morphological information obtained from measurements and experimental estimations. Then a high-efficiency lattice Boltzmann solver for the corresponding governing equations is described which, while assuring energy conservation and the appropriate continuities at numerous interfaces in a complex system, has demonstrated its numerical power in yielding accurate solutions. Various applications are provided to validate the feasibility, effectiveness and robustness of this new methodology by comparing the predictions with existing experimental data from different transport processes, accounting for the effects due to component size, material anisotropy, internal morphology and multiphase interactions. The examples given also suggest even wider potential applicability of this methodology to other problems as long as they are governed by the similar partial differential equation(s). Thus, for given system composition and structure, this numerical methodology is in essence a model built on sound physics principles with prior validity, without resorting to ad hoc empirical treatment. Therefore, it is useful for design and optimization of new materials, beyond just predicting and analyzing the existing ones.

Predictions of effective physical properties of complex multiphase materials

Evolution of the bioplastics industry has changed directions dramatically since the early 1990s. The latest generation is moving toward durable bioplastics having high biobased content. The main objective is to replace “fossil carbon” with “renewable carbon”, a holistic strategy to mitigate climate change by minimizing the environmental impact of a product throughout its life cycle. Durable bioplastics is desired for multiuse long-term application in automotive, electronics and other industries. One necessary requirement for them is to be both tough and strong, yet the two attributes are often mutually exclusive. Does this mean a biobased and biodegradable polymer as polylactic acid (PLA) with its high strength but low toughness cannot be adopted for durable applications? Well, not exactly; this is where the concept of tailoring the properties of PLA to achieve stiffness–toughness balance along with acceptable heat resistance comes into play. In this perspective, we summarize the recent research progress ...

http://pubs.acs.org/doi/pdf/10.1021/acssuschemeng.6b00321

Perspective on Polylactic Acid (PLA) based Sustainable Materials for Durable Applications: Focus on Toughness and Heat Resistance

Polylactic acid (PLA), one of the well-known biodegradable polyesters, has been studied extensively for tissue engineering and drug delivery systems, and it was also used widely in human medicine. A new method to synthesize PLA (ring-opening polymerization), which allowed the economical production of a high molecular weight PLA polymer, broad- ened its applications, and this processing would be a potential substitute for petroleum-based products. This review described the principles of the polymerization reactions of PLA and, then, outlined the various materials properties affect- ing the performance of PLA polymer, such as rheological, mechanical, thermal, and barrier properties as well as the pro- cessing technologies which were used to fabricate products based on PLA. In addition, the biodegradation processes of products which were shaped from PLA were discussed and reviewed. The potential applications of PLA in the medical fields, such as tissue engineering, wound management, drugs delivery, and orthopedic devices, were also highlighted.

http://www.expresspolymlett.com/letolt.php?file=EPL-0005820&mi=c

Properties and medical applications of polylactic acid: A review

Measurement of thermal conductivity of hollow glass-bead-filled polypropylene composites

The tensile properties of polypropylene (PP) composites filled separately with three kinds of graphene nano-platelets (GNPs) with different size were measured using a universal materials tester at room temperature and rate of extension of 50 mm/min. It was found that the values of the Young's modulus of the composites increased, the values of the tensile yield strength and tensile fracture of the composites increased slightly while the values of the tensile elongation at break decreased with increasing the GNPs weight fraction. The reinforcement of the composites could be attributed to the relatively big interfacial area and good interfacial adhesion between the matrix and the GNPs.

Tensile properties of graphene nano-platelets reinforced polypropylene composites

Simulation of heat transfer in hollow-glass-bead-filled polypropylene composites by finite element method

The poly( L -lactic acid) (PLLA) filled with nanometer calcium carbonate (nano-CaCO3) composites were prepared by means of a twin-screw extruder in the present paper. The nano-CaCO3 surface was treated with stearate. The crystalline properties of PLLA/nano-CaCO3 composites were measured using a differential scanning calorimeter, to identify the influence of the nanometer particle content on the crystalline properties. The results showed that the crystallization onset temperature, crystallization temperature and crystallization end temperature as well as the crystalline degree of the composites were obvious higher than those of the unfilled PLLA resin when the particle weight fraction (ϕf) was 1%, then they varied slightly. While the crystallization temperature interval decreased slightly. The improvement of crystallinity degree might be attributed to the heterogeneous nucleation of the nano-CaCO3 in the matrix.

Ji-Zhao Liang

Papers

Measurement of thermal conductivity of hollow glass-bead-filled polypropylene composites

Tensile properties of graphene nano-platelets reinforced polypropylene composites

Simulation of heat transfer in hollow-glass-bead-filled polypropylene composites by finite element method

Crystalline properties of poly(L-lactic acid) composites filled with nanometer calcium carbonate

Heat transfer in polymer composites filled with inorganic hollow micro-spheres: A theoretical model