Resistive-IR Hybrid Heating in FDM Printing

FDM printing is based on resistance to heat of the polymer filament, which starts in a viscous state and is extruded from nozzle to the printing area. The printing area is hot around 70°C for a better adherence of the deposited polymer and for slow cooling of it. The later deposited layers will experience faster cooling and the characteristics of the polymer will suffer light changes. The paper aims to present the results of a preliminary research regarding the double source successive heating and double source hybrid heating of the extruded polymer in FDM process. There were used two distinct heat sources, the resistive source mounted in the extrusion nozzle and IR lamp heat source placed in the printing chamber. The first heating, which acts during the extrusion process, is a hybrid heating and it is developed inside the extrusion nozzle (hot-end); it is given by the resistive heat source by the IR lamp. After the extrusion, during the deposition process and after the deposition process, the heating of the polymer continues due to the IR lamp. The difference between the printing with IR heating and without IR heating was monitored. A decreasing of about 5-8% of the material stiffness was noticed when the IR lamp was introduced. The material became more viscous and the bonding of the successive layers was improved. DSC analysis has been performed in both cases: with and without IR heat source. The evolution of the elastic modulus proved a decreasing of the plasticity during the simple printing process. The decreasing was less (at least by about 25%) when used IR heat source. The elongation viscosity was analysed and its values were decreasing while the temperature was increasing that took place. The decreasing was produced by the reduction of the elasticity, when the chain branches were decreasing their length. The decreasing is more pronounced while the increasing of the temperature. A low difference (of about 2-5%) was observed to the mechanical characteristics after tensile tests.

Toughness improvement of poly(lactic acid) by the addition of pre-crosslinked powdered nitrile rubber/CaCO3 for thermoforming molding

Polylactide (PLA) is an eco-friendly biodegradable thermoplastic with excellent processability, demanding less energy to be produced compared to the petroleum-based polymers. However, PLA has drawbacks that impose some restrictions of uses use such as poor toughness property. Blending PLA with other polymers is a more practical and economic way to improve its toughness. The present study assessed the effect of the addition of the pre-crosslinked powdered nitrile rubber (NBR) containing calcium carbonate (CaCO3) and extruder screw rotation on the mechanical, rheological, morphological and thermal properties of polylactide (PLA) by using a Central Composite Rotatable Design (CCRD) analysis, which provides statistical support for the experimental data. The results showed that NBR/CaCO3 can be used as toughness modifier for PLA. This property improved due to the increase in energy expended to deform the material and generate cracks, as showed in the impact and morphological analyzes. Despite this improvement, the presence of CaCO3 caused a slight decline in the thermal resistance of the composites. The influence of rubber (NBR/CaCO3) content in PLA matrix on rheological properties, such as elongation viscosity, melt strength and drawability was also investigated. The results showed that the composition PLA/NBR/CaCO3 with higher NBR/CaCO3 content can be used in thermoforming applications.

PP in 3D Printing - Technical and Economic Aspects

FDM is 3D printing technology using mainly PLA and ABS as filament materials. PP has close characteristics to PLA and, due to that, is a potential material for for deposition. Paper aims to analyse the behaviour of PP during heating cycle specific to 3D printing process. Macroscopic and microscopic analysis of the deposited strings have been performed. They revealed less stiffness of the PP deposition comparing to PLA, which is due to the lower viscosity of PP. DSC Thermal analysis has been done at it revealed a 30% higher heat flux in PP comparing to PLA and that increases its fluidity. It was recorded a difference between the elongation viscosity of the PP filament and the PP deposited by FDM process. After 5s the deposited PP proves higher values for the elongation viscosity. Dynamic shear rheology measurements the was applied on samples deformed under 210 kN at 190oC. It has been found that the PP requires lower storage energy and that means that it has a lower viscosity for the entire range of applied frequencies. In the same time, the complex viscosities prove different behavior. To improve the control of the deposition shape, it is necessary to reduce the extrusion temperature with 4-5%. That leads to economy in power consumption.

Laser Marking of PLA FDM Printed Products

The paper aimed to reveal, qualitatively and quantitatively, the modifications suffered by the PLA during the complex heating cycle specific to the 3D printing followed by laser marking. The obtained results showed that the melting point of the PLA decreases from 162.2oC (which is specific to PLA filament) to 153.1oC after the 3D printing process and to 149.7oC after the laser heating. The glass transition suffered the same lowering after the printing process but an important increasing after the laser heating. The elastic modulus evolution proved a decreasing of the plasticity and that is hapenning when the material suffers an increasing of its rigidity. The elongation viscosity was analyzed and its values were decreasing with the increasing of the temperature that happened on the material. The decreasing was produced by the reduction of the elasticity, when the chain branches are decreasing their length. The decreasing is more pronounced with the increasing of the temperature. The ratio between the loss modulus to the storage modulus and quantifies the way in which the PLA absorbs and disperses energy moves its peak from 65oC (curve specific to the PLA filament) to 45oC (curve specific to the last layer deposited by 3D printing process and re-heated by laser beam for marking). The peak means the lowest storage modulus, which is a measure of elastic response of a material, so the transition from glass to high elasticity moves to the lower temperatures.

Study on the Rheological Behaviour of Sisal Fibre/HDPE Composites with Flame Retardant

The rheological behaviour of sisal fibre/HDPE composites containing two types of flame retardants as magnesium hydroxide and ammonium polyphosphate was studied using a capillary rheometer. The mass ratio of HDPE to sisal fibre was set as 20 phr. Flame retardants were added at 10, 20 and 30 phr. Results showed that the composites exhibited pseudoplastic behaviour as the shear viscosity decreased with increasing shear rate. Shear stress and real shear viscosity increased with increasing flame retardant, with magnesium hydroxide giving higher values than ammonium polyphosphate. Therefore, magnesium hydroxide had a marked effect on the processing power, while ammonium polyphosphate did not greatly affect the shear viscosity of the composites. An increase in elongation rate reduced the elongation viscosity. The flame retardant contents had no significant effect on the elongation viscosity at high elongation rate. The materials showed increased extrudate swell with increasing apparent shear rate, but this significantly decreased with the addition of flame retardant. The power law index (n) for all composites was less than 1 and the flow consistency index K was higher for composites with flame retardant than those without. Moreover, magnesium hydroxide was more effective than ammonium polyphosphate causing an increase in the K value.

Heat Affected Zone in Microwave Polymer Welding

This paper aims to present some specific aspects regarding the heat affected zone in microwave polymer welding. It presents several results of investigation of the physical and mechanical modification of the HDPE100 polymer when the microwave heating is applied. Burst stress, elongation and relaxation modulus are subject of this research, as well as the information regarding the crystallization rate and elongation viscosity. To reveal the type of the structure and its transformation, Differential Scanning Calorimetry (DSC) was used. The recorded values for rate of crystallization are appropriate for the welding process, but it has negative effect when plastic deformation at high temperature (as in the extrusion process) is applied. The microwave heating produced a 12-20% decreasing of the plasticity with the increasing of the amount of heat introduced into the material (from 65 W power and 10 s heating to 130 W and 40 s). After the microwave heating, the material showed low values for the elongation viscosity, which means not very fluid material and a necessity to apply high temperatures during the processing by welding or plastic deformation.