Revealing the impact of ageing on a flame retarded PLA

Effect of Thermal and Hydrothermal Accelerated Aging on 3D Printed Polylactic Acid

In the new transformation of 'Industry 4.0', additive manufacturing technologies have become one of the fastest developed industries, with polylactic acid (PLA) playing a significant role. However, there is an increasing amount of garbage generated during the printing process and after prototypes or end-of-life parts. Re-3D printing is one way to recycle PLA waste from fused filament fabrication. To do this process successfully, the properties of the waste mixture should be known. Previous studies have found that PLA degrades hydrolytically, but the time at which this process occurs for 3D printed products is not specified. This work aims to establish the baseline of the degradation kinetics of 3D printed PLA products to predict the service time until which these properties are retained. To achieve this, 3D printed specimens were thermally and hydrothermally aged during several time intervals. Thermal and mechanical properties were also determined. This study reveals that tensile strength decreases after 1344 h of hydrothermal ageing, simulating 1.5-2.5 years of real service time. PLA therefore has the same thermo-mechanical properties before reaching 1.5-years of age, so it could be recycled.

Effect of Hygrothermal Ageing on the Mechanical and Fire Properties of a Flame Retardant Flax Fiber/Epoxy Composite

In engineering applications, natural fiber composites must comply with fire requirements including the use of flame retardant. Furthermore, biocomposites are known to be water sensitive. Whether flame retardants affect the water sensitivity and whether water absorption affects the fire behavior and the mechanical performance of biocomposites are the two main topics addressed in this work. In this study, a flax fiber/epoxy composite flame retardant with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or aluminum diethyl phosphinate (AlPi) was aged in humid atmosphere or by immersion in water. Water absorption kinetics revealed that DOPO induces an increase in equilibrium water content by approximately a factor of 2 due to its intrinsic hygroscopicity and/or its plasticizing effect on the epoxy matrix. In contrast, AlPi does not significantly change the water sensitivity of the biocomposite. Mechanical testing highlighted that, whatever the FR, the evolution of mechanical properties with ageing is governed by the moisture content. The drop of elastic modulus was attributed to a decrease in fiber rigidity due to plasticization, while the increase in tensile strength was assigned to an increase in fiber/matrix friction due to fiber swelling. As regards flame retardancy, only the highest water contents modified the fire behavior. For the AlPi containing biocomposite, the water release resulted in an increase by 50% of the time to ignition, while for the DOPO flame retardant biocomposite the water release was mainly postponed after ignition.

Flax/PP and Flax/PLA Thermoplastic Composites: Influence of Fire Retardants on the Individual Components

This study is based on previously reported reaction to fire properties of flax fibre-reinforced polymeric (polypropylene, PP and polylactic acid, PLA) composites, prepared by pre-treating the fabrics with different fire retardants (FRs) prior to composite preparation. It was observed that while all of these treatments were very effective in flax/PLA in terms of achieving a V-0 rating in a UL-94 test, only an organophosphonate FR was capable of achieving a V-0 rating for flax/PP. However, all fire-retardant treatments impaired the mechanical properties of the composites; the reduction was more in flax/PLA compared to flax/PP composites. To understand these effects further, here thermal analysis and pyrolysis combustion flow calorimetry of the composites and each component separately treated with FRs have been conducted and the results analysed in terms of the effect on each component so as to observe any interaction between the different components. The results indicated that in flax/PLA composites, the water released during FR catalysed dehydration-decomposition of flax may hydrolyse PLA, changing decomposition pathway of PLA to produce less flammable volatile, hence resulting in reduced flammability.

Two-year performance study of porous, thermoset, shape memory polyurethanes intended for vascular medical devices

The long-term shape-recovery behavior of shape memory polymers has often been shown to be dependent on the length of time the material has been stored in the secondary shape. Typically, recovery performance and shape fixity will decrease with increased time in the secondary shape. In medical materials, a shelf-life is crucial to establish as it sets the upper threshold for device performance in a clinical setting, and a reduction in shape recovery would limit the development of SMP medical devices. Here, we present a two-year study of strain recovery, strain fixity, and shape recovery kinetics for passively and actively actuated SMPs intended for vascular devices. While kinetic experiments using immersion DMA indicate slight material relaxation and a decrease in the time to recovery, these changes are not found for bulk recovery experiments. The results indicate that a two-year shelf-life for these SMPs is very reasonable, as there is no change in the recovery kinetics, strain recovery, or strain fixity associated with this aging time. Further, a thermal accelerated aging test is presented for more rapid testing of the shape memory behavior of these SMPs and is compared with the real time aging results, indicating that this test is a reasonable indicator of the two-year behavior.