Effects of physical aging on thermomechanical behaviors of poly(ethylene terephthalate)-glycol (PETG)

In Vitro Characterisation of 3D Printable Filaments Subjected to Edible Liquids: An Analysis of Fused Deposition Modelling for Intraoral Applicability

Purpose

To evaluate the influence of edible liquids on the characteristic properties of 3D printable materials compared to conventionally used dental resin acrylic.

Method

Dental polymethyl methacrylate (PMMA) specimens were fabricated from preformed molds while polylactic acid (PLA) and polyethylene terephthalate glycol (PETG) specimens were 3D printed using fused deposition modelling at 0.1 mm layer thickness. All specimen forms adhered to ISO 37:2017 and ISO 604:2002 specifications. Specimens underwent controlled immersion for 180 hr into different media (no immersion (control), oil, soda, milk, and caffeine). Changes in mass (g), plastic deformity (N/mm2), ultimate tensile stress (N), flexural deformity (N/mm2), and break force (N) were evaluated using analysis of variance.

Results

There was an increase in mass for all specimens following immersion with significant interactions between immersion media and the materials. The materials exhibited significant differences in plastic deformity (F (df) = 156.632(2), P  < 0.001), ultimate tensile stress (F (df) = 109.521(2), P  < 0.001), and break force (F (df) = 319.785 (2), P  < 0.001) with no significant interactions with immersion media (P > 0.05) on both accounts. Materials showed no significant differences in flexural deformity (F (df) = 2.693(2), P = 0.074) but with significant interactions (F (df) = 4.984(8), P  < 0.001) between acrylic and immersion media.

Conclusion

Commercially available 3D printable PLA and PETG filaments printed at 0.1 mm thickness possess approximately half the mechanical resilience as dental PMMA with comparable flexural deformity after exposure to edible liquids.

Examining the Flexural Behavior of Thermoformed 3D-Printed Wrist-Hand Orthoses: Role of Material, Infill Density, and Wear Conditions

This paper examined the mechanical properties of wrist-hand orthoses made from polylactic acid (PLA) and polyethylene terephthalate glycol (PETG), produced through material extrusion with infill densities of 55% and 80%. These orthoses, commonly prescribed for wrist injuries, were 3D-printed flat and subsequently thermoformed to fit the user's hand. Experimental and numerical analyses assessed their mechanical resistance to flexion after typical wear conditions, including moisture and long-term aging, as well as their moldability. Digital Imaging Correlation investigations were performed on PLA and PETG specimens for determining the characteristics required for running numerical analysis of the mechanical behavior of the orthoses. The results indicated that even the orthoses with the lower infill density maintained suitable rigidity for wrist immobilization, despite a decrease in their mechanical properties after over one year of shelf life. PLA orthoses with 55% infill density failed at a mean load of 336 N (before aging) and 215 N (after aging), while PETG orthoses did not break during tests. Interestingly, PLA and PETG orthoses with 55% infill density were less influenced by aging compared to their 80% density counterparts. Additionally, moisture and aging affected the PLA orthoses more, with thermoforming, ongoing curing, and stress relaxation as possible explanations related to PETG behavior. Both materials proved viable for daily use, with PETG offering better flexural resistance but posing greater thermoforming challenges.

Fused Filament Fabrication and Computer Numerical Control Milling in Cultural Heritage Conservation

This paper reports a comparison between the advantages and disadvantages of fused filament fabrication (FFF) and computer numerical control (CNC) milling, when applied to a specific case of conservation of cultural heritage: the reproduction of four missing columns of a 17th-century tabernacle. To make the replica prototypes, European pine wood (the original material) was used for CNC milling, while polyethylene terephthalate glycol (PETG) was used for FFF printing. Neat materials were chemically and structurally characterized (FTIR, XRD, DSC, contact angle measurement, colorimetry, and bending tests) before and after artificial aging, in order to study their durability. The comparison showed that although both materials are subject to a decrease in crystallinity (an increase in amorphous bands in XRD diffractograms) and mechanical performance with aging, these characteristics are less evident in PETG (E = 1.13 ± 0.01 GPa and σ = 60.20 ± 2.11 MPa after aging), which retains water repellent (ca = 95.96 ± 5.56°) and colorimetric (∆E = 2.6) properties. Furthermore, the increase in flexural strain (%) in pine wood, from 3.71 ± 0.03% to 4.11 ± 0.02%, makes it not suitable for purpose. Both techniques were then used to produce the same column, showing that for this specific application CNC milling is quicker than FFF, but, at the same time, it is also much more expensive and produces a huge amount of waste material compared to FFF printing. Based on these results, it was assessed that FFF is more suitable for the replication of the specific column. For this reason, only the 3D-printed PETG column was used for the subsequent conservative restoration.

From Virtual Reconstruction to Additive Manufacturing: Application of Advanced Technologies for the Integration of a 17th-Century Wooden Ciborium

3D modelling and 3D printing techniques have become increasingly popular in different fields, including cultural heritage. In this field, there are still many challenges to overcome, such as the difficulty of faithfully reproducing complex geometries or finding materials suitable for restoration, due to the limited scientific studies. This work proposes an example of the application of advanced technologies for the reproduction of four missing columns of a 17th century polychrome wooden ciborium. The difficulties of an automatic scan due to its reflective surface (water gilding and estofado decorations) were overcome by creating a 2D manual survey and a subsequent manual 3D redrawing. The CAD model was used to print the missing elements with fused filament fabrication (FFF) in polyethylene terephthalate glycol (PETG), using the following printing parameters: nozzle 0.4 mm, infill 20%, extrusion temperature of PLA 200 °C and of PETG 220 °C, plate temperature 50 °C, printing speed 60 mm/s, layer height 0.2 mm. The conservation and restoration of the ciborium is nearing completion. This study highlights the importance of collaboration between different professionals for the correct design of a restoration, as well as the need to promote scientific research into the development of new high-performance 3D printing materials suitable for conservation.

Effects of Fiber Orientation on the Coefficient of Thermal Expansion of Fiber-Filled Polymer Systems in Large Format Polymer Extrusion-Based Additive Manufacturing

Large format polymer extrusion-based additive manufacturing has been studied recently due to its capacity for high throughput, customizable bead size and geometry, and ability to manufacture large parts. Samples from three fiber-filled amorphous thermoplastic materials 3D printed using a Masterprint 3X machine from Ingersoll Machine Tools were studied, along with their neat counterparts. Characterization techniques included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermo-mechanical analysis (TMA). TGA results showed that the fillers decreased the degradation temperature for most of the materials investigated, with a 30 °C decrease for polycarbonate (PC) and a 12 °C decrease for polyethylene terephthalate glycol (PETG). For all the materials used, heat capacity increases with increasing temperature. Moreover, results show that a highly conductive filler increases the heat capacity. In contrast, a material with a lower conductivity decreases the heat capacity indicated in the 15.2% and 2.54% increase for acrylonitrile butadiene styrene (ABS) and PC and a 27.68% decrease for PETG. The TMA data show that the printed bead exhibits directional properties consistent with an orthotropic material. Smaller strains and coefficient of thermal expansion (CTE) were measured along the bead direction and across the bead compared to the through bead thickness showing that fillers are predominantly oriented in the bead direction, which is consistent with the literature. CTE values through bead thickness and neat material are similar in magnitude, which corresponds to the CTE of the matrix material. The experimental results serve to characterize the effect of fiber filler on the part thermal strains in three principal directions and two-part locations during the extrusion and bead deposition of large-format polymer extrusion-based additive manufacturing technologies.

Glass Transition Behavior of Wet Polymers

We have performed a systematical investigation on the glass transition behavior of amorphous polymers with different solvent concentrations. Acrylate-based amorphous polymers are synthesized and treated by isopropyl alcohol to obtain specimens with a homogenous solvent distribution. The small strain dynamic mechanical tests are then performed to obtain the glass transition behaviors. The results show that the wet polymers even with a solvent concentration of more than 60 wt.% still exhibit a glass transition behavior, with the glass transition region shifting to lower temperatures with increasing solvent concentrations. A master curve of modulus as a function of frequency can be constructed for all the polymer-solvent systems via the time-temperature superposition principle. The relaxation time and the breadth of the relaxation spectrum are then obtained through fitting the master curve using a fractional Zener model. The results indicate that the breadth of the relaxation spectrum has been greatly expanded in the presence of solvents, which has been rarely reported in the literature. Thus, this work can potentially advance the fundamental understanding of the effects of solvent on the glass transition behaviors of amorphous polymers.

Thermal, structural and morphological characterization of dental polymers for clinical applications

PURPOSE

Polymers are used in dentistry on a daily basis due to their mechanical, functional and aesthetic properties. However, such biomaterials are subject to deterioration in the oral environment. Thus, this study aimed to evaluate the structural properties of five commonly used dental polymers to determine their best clinical indications.

METHODS

Four hundred-fifty samples of five dental polymers (polyethylenterephthalat - glycol modified (PG), polymethyl methacrylate (PA), ethylene vinyl acetate(E), polycarbonate (PC), polyetheretherketone (PK) were prepared to investigate their thermal, structural and chemical characteristics using energy dispersive spectroscopy (EDS), Fourier transform infrared analysis(FTIR), scanning electron microscopy (SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), X-ray diffraction(XRD), and Shore D hardness test. Data were analyzed using one-way ANOVA, Tukey's HSD, and Levene's tests (α=0.05).

RESULTS

PK (87.2) and PA (82.4) displayed the highest hardness values and smooth surfaces, as observed with SEM (p<0.001). Silica was detected in PK, PA, and E by EDS and XRD. The highest glass transition temperature was recorded for PC (145.00±2.00°C) and PK (143.00±1.87°C), while the lowest value was measured for E (50.00±2.12°C)(p<0.001).The highest mass loss was detected for PG (91.40±1.40%) by TGA.

CONCLUSIONS

PA and PK polymers can be used for stress-containing treatments due to their mechanical properties. These two materials are also advantageous in terms of plaque accumulation as these polymers reveal smoother surfaces than other groups. Insufficient physical and thermal properties require the use of E with caution and only in limited clinical indications.

Long-Term Physical Aging Tracked by Advanced Thermal Analysis of Poly(N-Isopropylacrylamide): A Smart Polymer for Drug Delivery System

Poly(N-isopropylacrylamide) (PNIPA), as a smart polymer, can be applied for drug delivery systems. This amorphous polymer can be exposed on a structural recovery process during the storage and transport of medicaments. For the physical aging times up to one year, the structural recovery for PNIPA was studied by advanced thermal analysis. The structural recovery process occurred during the storage of amorphous PNIPA below glass transition and could be monitored by the differential scanning calorimetry (DSC). The enthalpy relaxation (recovery) was observed as overshoot in change heat capacity at the glass transition region in the DSC during heating scan. The physical aging of PNIPA was studied isothermally at 400.15 K and also in the non-isothermal conditions. For the first time, the structural recovery process was analyzed in reference to absolute heat capacity and integral enthalpy in frame of their equilibrium solid and liquid PNIPA.