Sustainable sulfur polymers for environmental remediation and multifunctional composite materials

Author: Nic Lundquist

Lundquist, Nic, 2021 Sustainable sulfur polymers for environmental remediation and multifunctional composite materials, Flinders University, College of Science and Engineering

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Historically elemental sulfur, a waste product of the petroleum refining process, has been difficult to process into useful polymeric forms. The recent development of inverse vulcanisation has allowed for the stabilisation of high sulfur content polymers leading to a wide variety of new sulfur-based materials with interesting chemical and physical properties. In this thesis inverse vulcanisation was utilised to prepare sustainable high sulfur content polymers from renewable plant oils (canola oil) and waste cooking oils. Porous versions of these polymers were prepared by using a NaCl porogen during the inverse vulcanisation reaction. This porogen was then removed after synthesis by washing the product with water, leaving behind a high surface area porous polymer structure. This was an important step for increasing the efficiency of these materials in sorption-based applications. Another important development was the use of microwave irradiation to facilitate the rapid inverse vulcanisation of sulfur and canola oil in 5 minutes, compared to the 30 minutes required under conventional heating. The ability to use household microwaves to prepare this material make it far more accessible to remote areas with limited resources. This is especially true for the application of environmental remediation whereby remote areas with limited resources require access to efficient water treatment technologies. Sulfur polymers have previously been investigated as sorbent materials for heavy metal remediation with most studies focusing on mercury pollution remediation. This thesis focused on using a sorbent material prepared from the inverse vulcanisation of sulfur with canola oil for the remediation of iron pollution. These sorbents were shown to effectively reduce the Fe(III) concentrations to below regulation limits. Removal of Fe(II) was also achieved by oxidising the Fe(II) to Fe(III) using H2O2 followed by treatment with the polymer sorbent. The use of waste cooking oil instead of food grade canola oil to prepare the polymer was shown not to impact the performance of the sorbent material. This was an important discovery as it means that waste cooking oil can be used instead of food grade oil, demonstrating a further advancement in the field of waste valorisation. To further the scope of these sulfur materials in the field of environmental remediation, their use as polymeric support materials for the stabilisation of powdered activated carbon (PAC) was demonstrated. The poly(S-r-canola) support facilitated the effective use of PAC in continuous flow treatment processes as well as increased its safety profile by suppressing the generation of flammable PAC dust plumes. The PAC / poly(S-r-canola) blend was demonstrated to be an effective sorbent material for the remediation of the persistent organic pollutants perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), outperforming the current industry standard, granular activated carbon (GAC). Although a wide variety of important applications for these sulfur polymers have been investigated, efficient end of life recycling strategies have not been yet developed. In this thesis a new


method for reforming, repurposing, and recycling sulfur polymers termed reactive compression moulding was developed. This process involved compressing poly(S-r-canola) particles reactive interfaces into direct contact under heat, whereby a sulfur exchange reaction would occur facilitating the chemical binding of neighbouring particles. Different types and amounts of filler materials were combined with the polymer during reactive compression moulding to allow for the mechanical properties of the resulting mats/blocks to be tailored for specific applications. This simple recycling/reforming process was then further utilized to prepare multifunctional magnetic composite materials. To achieve this, magnetic !-Fe2O3 nanoparticles were combined with poly(S-r-canola) particles before undergoing reactive compression moulding to effectively encapsulate the nanoparticles. The resulting composite materials were shown to maintain their ability to remove HgCl2 from solution whilst also allowing for magnetic filtration to be used to isolate the spent sorbent from other solids in solution reducing the quantities of solid waste being produced. The inclusion of the magnetic particles also facilitated the heating of these composites through microwave irradiation. The heating rate was shown to be directly proportional to the amount of !-Fe2O3 nanoparticle in the composite material allowing for the determination of optimized irradiation times for each composite. Using this information rapid reactive compression moulding of the composite material, forming composite disks and cylinders, was demonstrated under microwave irradiation. Finally, the use of these magnetic composites in electrical and mechanical systems was demonstrated by replacing the active magnetic component in a solenoid valve with the magnetic composite material. This reduced the weight of the component by an order of magnitude and demonstrated one of many potentials uses within electrical and mechanical systems.

Keywords: Sulfur, Polymers, Inverse vulcanisation, remediation, composites

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2021
School: College of Science and Engineering
Supervisor: Associate professor Justin Chalker