Bioconversion of specified risk materials-derived peptides for tackifier and torrefied wood binder applications

• Author / Creator

  Shui, Tao

• Due to the safety concerns relating to the spread of bovine spongiform encephalopathy (BSE) or ‘mad cow disease’ in North America, strict bans for specified risk materials (SRMs) have been introduced to the rendering process. SRMs are characterized as the tissues in cattle where misfolded proteins, the possible infection source for BSE, are concentrated. According to those bans, SRMs are required to be segregated and disposed strictly, resulting in significant additional costs to companies. To relieve the economic pressure on rendering industries, an approved SRM disposal method, thermal hydrolysis, is followed to convert these proteinaceous waste materials into non-infective peptides. Due to the binding property, water solubility and bio-degradability displayed in the obtained SRM-derived peptides, these peptides have been examined as a promising feedstock for the development of value-added bio-based products. Here, the purpose of this research was to valorize SRM-derived peptides for commercially competitive binders, such as tackifiers and torrefied wood binder.
  As a binding agent in hydro-mulch mixtures, tackifiers are employed to bind seed and mulch fibres to the soil to restore the vegetation in eroded areas. In addition to the binding property, tackifiers must also achieve a great balance between water resistance and water-holding capacity: water resistance or hydrophobicity is required to prevent diffusion and loss of function caused by rain-wash; water-holding capacity helps to maintain the necessary moisture for the rooting and growth of plants. To first increase the hydrophobicity, a glutaraldehyde cross-linking strategy was introduced to the SRM-derived peptides. Moreover, both the binding property and water-holding capacity of the resulting products were assessed to compare with unmodified peptides, showing no sacrifice in these performance measures.
  To improve the binding property and water-holding capacity of SRM-derived peptides, epoxidized poly (vinyl alcohol) (PVA) was synthesized and employed as a cross-linking agent for peptides-based tackifier development. The resulting cross-linking products displayed higher binding strength with adjustable water-holding capacity than unmodified peptides. The performance of the cross-linked products was even comparable to commercially available tackifiers. Hence, the two cross-linking strategies examined in this research demonstrated a novel valorization pathway of converting SRM-derived peptides into sustainable tackifiers.
  As a renewable source of fuels, torrefied wood pellets are produced to handle growing energy demands and the environmental concerns relating to the utilization of conventional fossil fuel. To improve the competitiveness of torrefied wood pellets against other source of fuels, i.e., coals, torrefied wood binder was studied as an extra pellet additive, and was expected to increase energy density, durability, and storage life of torrefied wood pellets.
  Based on the binding property shown in the tackifiers study, I started with SRM-derived peptides to develop a novel binder for pellet industries, but found that unmodified peptides didn’t help to improve the strength of pellets. This finding made the cross-linking strategy necessary for SRM-derived peptides, leading to the concept of using PVA-EPC-Peptides as a binder for pellets production. PVA-EPC-Peptides (EPC stands for epicholohydrin) is a cross-linked product obtained from the reaction between SRM-derived peptides and epoxidized PVA, which displayed higher binding strength than unmodified peptides in tackifier study. It was observed in this research that the pellets produced with 3.0 wt.% of PVA-EPC-Peptides exhibited higher compression strength than that of the pellets produced without any binder, via the following densification conditions: a die temperature of 150℃, 250 MPa holding pressure, 1 min holding time, and a 3.0 wt.% moisture content of the binder/wood mixture. The density of the pellets produced with 3.0 wt.% of PVA-EPC-Peptides was also found higher than that of the pellets produced without any binder. Therefore, this research demonstrates another feasible valorization pathway of converting SRM-derived peptides into a torrefied wood binder.
  In summary, this research has provided a technology platform by which the otherwise hazardous proteinaceous waste, SRMs, can be valorized into tackifiers and torrefied wood binders. This technology platform is developed not only to produce an alternative income for the rendering companies, but also to create sustainable products that satisfy the related industries.

• Subjects / Keywords

  • Peptides Cross-linking
  • Bio-Conversion
  • Specified Risk Materials
  • Tackifiers
  • Torrefied wood binders

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-hpj3-em50

• License

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