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      A process for melt grafting itaconic anhydride onto polyethylene

      Hanipah, Suhaiza Hanim
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      Hanipah, S. H. (2008). A process for melt grafting itaconic anhydride onto polyethylene (Thesis, Master of Engineering (ME)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/2462
      Permanent Research Commons link: https://hdl.handle.net/10289/2462
      Abstract
      Currently, extensive research in using bio‐derived polymers is being done, highlighting the

      importance of sustainable, green polymeric materials. Some sustainable alternatives to

      synthetic polymers include lignin, starch, cellulose or blends of these with petroleum‐based

      polymers.

      In New Zealand, large quantities of animal derived proteins are available at very low cost,

      making it ideal as a sustainable alternative to petroleum‐derived polymers. However, the

      processability of most proteins is very difficult, but can be improved by blending with synthetic

      polymers, such as polyolefins. To improve, the compatibility between these substances, a

      functional monomer could be grafted onto the polyolefin chain. Using an appropriate functional

      group, the polyolefin could then react with certain amino acids residues in the protein. Lysine

      and cystein are the two most appropriate amino acid residues because of their reactivity and

      stability at a wide pH range.

      In this study, free radical grafting of itaconic anhydride (IA) onto polyethylene was investigated.

      IA was selected because it is capable of reacting with polyethylene and amino acid residues,

      such as lysine. The objective of the research was to identify and investigate the effect of

      reaction parameters on grafting. These were: residence time, temperature, initial monomer

      concentration as well as peroxide concentration and type. Grafting was characterized in terms

      of the degree of grafting (DOG), percentage reacted and the extent of side reactions.

      The reaction temperature was taken above the melting point of the polyethylene, monomer

      and decomposition temperature of the initiator. It was found that above 160 C polymer

      degradation occurred, evident from sample discolouration. A higher degree of grafting can be

      achieved by increasing the initial monomer concentration up to a limiting concentration. The

      highest DOG achieved was about 1.2 mol IA per mol PE, using 2 wt% DCP. When using 2 wt %

      peroxide, the limiting concentration was found to be 6 wt% IA, above which no improvement in

      DOG was achieved. It was found that DCP is much more effective at grafting, compared to DTBP

      because DTBP is more prone to lead to side reactions than DCP.

      iv

      It was found that a residence time of 168 seconds resulted in the highest DOG, corresponding to

      4 extrusions in series. However, it was also found that an increase in residence time resulted in

      an increase in polymer degradation. The tensile strength of PE decreased after two extrusions

      when using DTBP, and three extrusions, when using DCP. Young's modulus decreased only

      slightly, while all samples showed a dramatic decrease in ductility, even after one extrusion. It

      was concluded that degradation had a more pronounced effect on mechanical properties than

      cross‐linking, and residence time should therefore not exceed three extrusions in series, which

      corresponded to about 126 seconds.

      It can be concluded that a high reaction temperature and high initiator concentration lead to a

      low degree of grafting, accompanied by high cross‐linking and increased degradation. On the

      other hand, high monomer concentration and high residence time lead to a high degree of

      grafting.

      Optimising grafting is therefore a trade off between maximal DOG and minimising side reactions

      such as cross‐linking and degradation and optimal conditions do not necessarily correspond to a

      maximum DOG. Other factors, such as the use of additives to prevent degradation should also

      be investigated and may lead to different optimum conditions.
      Date
      2008
      Type
      Thesis
      Degree Name
      Master of Engineering (ME)
      Publisher
      The University of Waikato
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