skip to main content


Title: Effect of Architecture on Silk/Resin Wettability for Silk Reinforced Composites
In the last few decades, fiber reinforced composites have been established as the materials of choice for lightweight applications in a large spectrum of applications ranging from aerospace, defense, and marine industries to automotive products and consumer goods. With the growing shift to sustainable resources, natural fibers, especially plant fibers, received increased interest throughout the years. Among these natural fibers, silks stand out with low stiffness and a high failure strain, unlike conventional fibers such as carbon or glass. Although gaining traction as a natural alternative reinforcement, silk still has little to no commercial uses despite its higher performance. Besides its higher mechanical properties and lightweight, silk exhibits other attractive properties such as improved flame retardancy and biodegradability. To take advantage of these features, proper fiber/matrix adhesion must be achieved. Such silk/matrix bonding can be inferred from the silk/resin affinity during composite manufacturing. In this study, the affinity/wettability of several silk/resin systems were analyzed via static contact angles using imageJ software to determine candidates for silk reinforced composite laminates with better adhesion. To this end, a combination of four silk fibers and three resin systems were investigated. The investigated silk fibers were Ahimsa, Charmeuse, Habotai, and Tussah; and the resins included a vinyl ester (Hydrex) and two epoxies (INF114 and INR). For Tussah fibers, initial contact angles were consistently one of the lowest. However, these fibers exhibited a higher contact angle over time compared to the other silk fibers studied. Conversely, Ahimsa silk fibers showed the highest initial contact angle, then quickly dropped to com-plete wetting. Habotai fibers dropped towards complete wetting quickly, however, consistently slowed considerably shortly after. Charmeuse fibers performed similarly to Ahimsa fibers with Hydrex, however was considerably slower to wetting with the other resins. Among the investigated resins, Hydrex showed the best affinity to silk fibers with the majority of the lowest initial contact angles and the fastest to complete wetting. INF114 consistently receded at a slower, albeit steady, rate until reaching complete wetting apart from Tussah. INR showed the highest initial contact angles and never reached complete wetting after an hour for two of the four silks investigated. Therefore, the best silk/resin affinity was observed for the Ahimsa and Charmeuse silk fibers and the Hydrex vinyl ester resin. In future work, silk composites with these constituents would be investigated.  more » « less
Award ID(s):
1928622
PAR ID:
10341618
Author(s) / Creator(s):
Date Published:
Journal Name:
American journal of advanced research
Volume:
5
Issue:
December
ISSN:
2572-8830
Page Range / eLocation ID:
1-6
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Thanks to its comparable specific mechanical properties to glass fibers, silk is a natural fiber that can be used as an eco-friendly alternative to synthetic reinforcing fibers in composite materials. Compared to natural fibers, especially plant fibers, silk enjoys higher mechanical performances, lower density, and higher elongation even at low temperatures, silk also exhibits other attractive qualities like flame resistance and being naturally continuous. However, silk is known to be prone to moisture absorption from surrounding humid environments. Moisture absorption may alter the silk/resin dynamics during composite manufacturing, and later lead to prem-ature degradation in the composite thermomechanical properties. This study investigates the effect of humidity on silk/resin wettability using two different resins (one epoxy and one vinyl ester) and three different silk architectures. Silk fibers are first exposed to different relative humidity environments. Subsequently, the affinity of the conditioned silk to a set of resins is assessed through measurements of silk/resin contact angle over time. Different silk/resin systems were observed to have contrasting responses to humidity exposure. While some silk/resin systems, such as Ahimsa/epoxy, did not show any change after humidity exposure. Other combinations showed tremendous susceptibility of silk/resin affinity to prior exposure of silk to humidity. For instance, although starting at virtually the same initial hydrophobic contact angle of ~123 degrees, Habotai silk/epoxy samples had contrasting wetting times. While the dried Habotai silk reached full wetting after around 5 minutes, the silk samples exposed to humidity took around 1 hour to reach full im-pregnation. These findings demonstrate the importance of humidity exposure control in silk reinforced composites. Keywords: Natural-Fiber Composites, Contact Angle, Silk, Wettability, Humidity. 
    more » « less
  2. Silk fibroin (SF) is a protein polymer derived from insects, which has unique mechanical properties and tunable biodegradation rate due to its variable structures. Here, the variability of structural, thermal, and mechanical properties of two domesticated silk films (Chinese and Thailand B. Mori) regenerated from formic acid solution, as well as their original fibers, were compared and investigated using dynamic mechanical analysis (DMA) and Fourier transform infrared spectrometry (FTIR). Four relaxation events appeared clearly during the temperature region of 25 °C to 280 °C in DMA curves, and their disorder degree (fdis) and glass transition temperature (Tg) were predicted using Group Interaction Modeling (GIM). Compared with Thai (Thailand) regenerated silks, Chin (Chinese) silks possess a lower Tg, higher fdis, and better elasticity and mechanical strength. As the calcium chloride content in the initial processing solvent increases (1%–6%), the Tg of the final SF samples gradually decrease, while their fdis increase. Besides, SF with more non-crystalline structures shows high plasticity. Two α- relaxations in the glass transition region of tan δ curve were identified due to the structural transition of silk protein. These findings provide a new perspective for the design of advanced protein biomaterials with different secondary structures, and facilitate a comprehensive understanding of the structure-property relationship of various biopolymers in the future. 
    more » « less
  3. Abstract

    Animal silks, consisting of pure protein components, offer an extraordinary combination of strength, elongation, and toughness, exceeding most engineered materials. The secret to this success is their unique nanoarchitectures formed through the hierarchical self‐assembly of silk proteins. This natural process contrasts the production of artificial silk materials, which usually are directly constructed as bulk structures from silk fibroin (SF) molecules. A variety of fabrication strategies to control nanostructures of silks or to create functional materials from silk nanoscale building blocks have been developed in the recent years. These emerging fabrication strategies offer an opportunity to tailor the structure of SF at the nanoscale and provide a promising route to produce structurally and functionally optimized silk nanomaterials. Herein, the critical roles of silk nanoarchitectures in property and function of natural silk fibers are reviewed and the strategies of utilization of these silk nanobuilding blocks are outlined. Further, the state‐of‐the‐art techniques to create silk nanoarchitectures and to generate silk‐based nanocomponents are summarized. An effective approach to constructing sophisticated silk functional nanocomposites with promising applications in regenerative medicine, drug delivery, and optical and electronic device designs is provided. Further, such insights suggest templates to consider for other material systems.

     
    more » « less
  4. Macqueen, D (Ed.)
    Abstract Spider silks are renowned for their high-performance mechanical properties. Contributing to these properties are proteins encoded by the spidroin (spider fibroin) gene family. Spidroins have been discovered mostly through cDNA studies of females based on the presence of conserved terminal regions and a repetitive central region. Recently, genome sequencing of the golden orb-web weaver, Trichonephila clavipes, provided a complete picture of spidroin diversity. Here, we refine the annotation of T. clavipes spidroin genes including the reclassification of some as non-spidroins. We rename these non-spidroins as spidroin-like (SpL) genes because they have repetitive sequences and amino acid compositions like spidroins, but entirely lack the archetypal terminal domains of spidroins. Insight into the function of these spidroin and SpL genes was then examined through tissue- and sex-specific gene expression studies. Using qPCR, we show that some silk genes are upregulated in male silk glands compared to females, despite males producing less silk in general. We also find that an enigmatic spidroin that lacks a spidroin C-terminal domain is highly expressed in silk glands, suggesting that spidroins could assemble into fibers without a canonical terminal region. Further, we show that two SpL genes are expressed in silk glands, with one gene highly evolutionarily conserved across species, providing evidence that particular SpL genes are important to silk production. Together, these findings challenge long-standing paradigms regarding the evolutionary and functional significance of the proteins and conserved motifs essential for producing spider silks. 
    more » « less
  5. Abstract

    Darwin’s bark spider (Caerostris darwini) produces giant orb webs from dragline silk that can be twice as tough as other silks, making it the toughest biological material. This extreme toughness comes from increased extensibility relative to other draglines. We showC. darwinidragline-producing major ampullate (MA) glands highly express a novel silk gene transcript (MaSp4) encoding a protein that diverges markedly from closely related proteins and contains abundant proline, known to confer silk extensibility, in a unique GPGPQ amino acid motif. This suggestsC. darwinievolved distinct proteins that may have increased its dragline’s toughness, enabling giant webs.Caerostris darwini’sMA spinning ducts also appear unusually long, potentially facilitating alignment of silk proteins into extremely tough fibers. Thus, a suite of novel traits from the level of genes to spinning physiology to silk biomechanics are associated with the unique ecology of Darwin’s bark spider, presenting innovative designs for engineering biomaterials.

     
    more » « less