Comparison of thermal, mechanical and thermomechanical properties of poly(lactic acid) injection-molded into epoxy-based Rapid Prototyped (PolyJet) and conventional steel mold

Abstract

The number of renewable resource based and inherently biodegradable Poly(Lactic Acid) (PLA) products are growing in the market, resulting in an increasing demand to produce even small series of injection molded PLA prototypes for testing purposes by using rapid molds. In our research it was first demonstrated that it is possible to use epoxy based molds made by PolyJet Rapid Prototyping technology for conventional injection molding to produce small series of PLA parts. The effect of mold material, namely conventional steel mold and epoxy based PolyJet mold was analyzed on the thermal and mechanical properties of the injection molded products.PLA was used with no, moderate and high nucleating agent content (Talc and Poly(Ethylene Glycol)) to obtain a model material with slow, moderate and high crystallization rate respectively. It was demonstrated that the mold used and thus the thermal conductivity of the mold had significant effect on the crystallinity of the PLA parts and thus on its' mechanical and thermomechanical properties. Finally, it was found that it is possible to mimic the thermomechanical properties of nucleated PLA injected into hot mold used for mass production by injecting it into the epoxy based PolyJet mold used for small series production.3

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

“…Unique approach of using epoxy based PolyJet mold instead of steel mold for conventional injection molding to produce PLA parts with high crystallinity has been proposed to offer promising results ( Table 2). 95 Because of low thermal conductivity of epoxy based PolyJet mold, PLA parts containing nucleating agents produced from this mold had a significantly higher level of crystallinity, thermal and mechanical properties compared to PLA samples molded from steel molds. When PLA is injected into 23°C steel mold, it is cooled below its T g in 15 s due to high thermal conductivity of the steel mold, whereas, in PolyJet mold, PLA material stays above T g for around 66 s, allowing the material to crystallize.…”

Creep behaviour of injection-moulded basalt fibre reinforced poly(lactic acid) composites

“…Nucleating agents can be used for enhancing crystallization, but it is still challenging to develop high or even the possible maximum crystallinity of around 40-50% during processing. 37 According to the basalt fibre reinforced PLA samples, the first heating scan was analysed and the thermal history was not erased, thus the crystallinity values represent the crystallinity of the injection moulded specimens ( As it can be seen, the addition of basalt fibres to PLA did not significantly modify the transition temperatures, moreover and most importantly it also had only low effect on the crystallinity values.…”

Physical integrity of 3D printed parts for use as embossing tools

“…This relationship has been studied previously in respect to tensile stress [10][11][12][13], surface roughness [10], and thermomechanical properties [14].…”