Simultaneous rheology and cure kinetics dictate thermal post-curing of thermoset composite resins for material extrusion

Romberg, Stian K.; Kotula, Anthony P.

doi:10.1016/j.addma.2023.103589

Cited by 8 publications

(24 citation statements)

References 80 publications

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“…However, the addition of 5% or 10% fumed silica prevents such a drop in storage modulus below a baseline value. 39 Although the systems are different, a similar phenomenon may be happening here.…”

Section: Fracture Surfacesmentioning

confidence: 60%

“…Conversely, in the SMP-10-Z ink, the viscosity of the PCS resin would be expected to decrease significantly, which would make it easier for voids form and grow through coalescence. Romberg and Kotula 39 have recently studied the relationship between rheological properties and extent of cure in an epoxy resin, that is, frequently used for material extrusion AM. They showed that upon thermal curing, the storage modulus drops precipitously from the room temperature value before it increases due to crosslinking.…”

Section: Fracture Surfacesmentioning

confidence: 99%

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Size effects in 3D‐printed polymer‐derived, zirconium diboride‐reinforced ceramic composites

Kemp,

Reed,

Compton

2023

J Am Ceram Soc.

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Preceramic polymers are of interest for use in many manufacturing techniques such as injection molding, ceramic fiber infiltration, and additive manufacturing. However, off‐gassing of low molecular weight oligomers occurs when these polymers cure, potentially leading to porosity in the cured part. To study how porosity and strength are affected by the size of the printed part, and the presence of a high surface area nano‐scale filler, polycarbosilane (PCS) microrods of varying diameter were fabricated via direct ink writing (DIW), an additive manufacturing technique, with two ink formulations containing either zirconium diboride (ZrB2) alone, or ZrB2 and fumed alumina (FA). Sets of microrods were printed in a range of sizes by using print nozzles of 450, 634, 979, 1 346, or 1 702 μm in diameter, which were thermally cured, pyrolyzed to form ceramic composite microrods, and tested in 3‐pt flexure. Porosity increased with increasing diameter, while failure strength decreased. For a given nozzle size, the microrods containing FA displayed lower porosity and higher strength (up to ∼500 MPa) compared to the microrods containing only ZrB2. Weibull strength analysis was performed on each group of microrods and shows that the addition of FA increased Weibull modulus from 4.63 ± 1.56 to 9.35 ± 0.601. In conjunction with optical microscopy, this analysis indicates two distinct flaw populations in the printed materials, porosity which arises during the curing step and cracking which arises during pyrolysis of the larger specimens.

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Section: Fracture Surfacesmentioning

confidence: 60%

Section: Fracture Surfacesmentioning

confidence: 99%

Size effects in 3D‐printed polymer‐derived, zirconium diboride‐reinforced ceramic composites

Kemp,

Reed,

Compton

2023

J Am Ceram Soc.

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“…Experimental measurements of diepoxy−diamine systems indicate a gel point 0.66 < α gel < 0.80. 3,7,66 Percolation predictions using the Zimm and Rouse models suggest s ranges from 0 to 1.35, 2 and experimental values of s have been found between 0.75 and 1.5. 2,67 The power-law model can be rearranged to explicitly solve for conversion as…”

Section: Resultsmentioning

confidence: 99%

“…The critical gel conversion α gel predicted from the GEM model (Table 1) falls below the value found by the power-law and Castro−Macosko models, but still within the range expected by Flory−Stockmayer theory (0.58) and experimental results (0.66 < α < 0.80). 3,7,66 These measurements of critical gel conversion exceed the Flory−Stockmayer theory, suggesting that defects like dangling chains and intramolecular bonds (which are not considered in the theory) form within the resin during the curing process. The scaling exponent s from the GEM fit is closer to the upper bound of theoretical and experimental values (0 ≤ s ≤ 1.5) 1,2,39 reported in the literature than the s determined by the power-law model (which only considers pregel data).…”

Section: Generalized Effective Medium Modelmentioning

confidence: 85%

“…53 Using this peak to track conversion, rheo-Raman measurements have shown the nonlinear correlation between conversion and rheological properties. 7,54 Additional analysis of the simultaneous conversion and rheology data provided by these types of instruments can be used to evaluate current models and develop models that more accurately relate cross-linking behavior to rheology.…”

Section: Introductionmentioning

confidence: 99%

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Evaluating Models That Predict Epoxy Conversion Using Rheological Properties

Romberg,

Roberts,

Snyder

et al. 2024

ACS Appl. Polym. Mater.

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Simultaneous rheology and conversion measurements of neat and composite epoxy resins reveal that conventional models neither accurately nor fully describe the relationship between rheology and conversion. We find that models predicting thermoset conversion based on mixing rules of rheological properties are quantitatively inaccurate and do not account for chemical gelation. Models based on percolation theory and the divergence of the viscosity at the gel point are more accurate but valid only before the gel point. Here, we propose the use of the generalized effective medium (GEM) model, which incorporates the divergence of the rheological properties on both sides of the critical gel point. We show that the GEM model works well for both neat resins and filled systems, and the resulting parameters estimate the gel point and scaling behavior on either side of the sol−gel transition.

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