VT PowerPoint Template5

1. Starch for Renewable Materials

3. Separated Starch Granules Starch granules have structural hierarchy.Starch granules have structural hierarchy.

4. Starch Structure Takes you from macro to molecular scale. Alternating rings of amorphous amylose and partially crystalline amylopectin. Counter-intuitive b/c you would expect linear chains to pack into crystals and branched chains to inhibit this process. However, amylopectin is such a large molecular weight that portions of it will arrange into double helices (just like DNA!), I.e., two chains twisting in unison. The helices are radial (along) to the granule surface so the crystals are tangential to the surface. Most synthetic polymers will have crystals arranged radially (along) on the surface with the chains tangential to the surface, PP may be an exception. This is an example of biosynthesis giving a unique and unexpected result. Amorphous linear amylose suggests that its interaction with other amylose molecules is limited because amylopectin gets in its way. The higher amorphous content relative to cellulose is probably also a reason it is processable.Takes you from macro to molecular scale. Alternating rings of amorphous amylose and partially crystalline amylopectin. Counter-intuitive b/c you would expect linear chains to pack into crystals and branched chains to inhibit this process. However, amylopectin is such a large molecular weight that portions of it will arrange into double helices (just like DNA!), I.e., two chains twisting in unison. The helices are radial (along) to the granule surface so the crystals are tangential to the surface. Most synthetic polymers will have crystals arranged radially (along) on the surface with the chains tangential to the surface, PP may be an exception. This is an example of biosynthesis giving a unique and unexpected result. Amorphous linear amylose suggests that its interaction with other amylose molecules is limited because amylopectin gets in its way. The higher amorphous content relative to cellulose is probably also a reason it is processable.

5. Starch Molecules While starch does structure quite a bit, the branching and helices do not allow it to structure as completely as linear cellulose (draw situation on board) so it is easier to overcome structure to process.While starch does structure quite a bit, the branching and helices do not allow it to structure as completely as linear cellulose (draw situation on board) so it is easier to overcome structure to process.

7. Plasticization

8. The literature is confusing and describes �thermoplastic�, �destructurized�, �gelatinized�, and �plasticized� starch. They are all the same thing: structure is overcome with a combination of plasticizer, heat, and pressure to get starch into a processable state. One difference seems to be that thermoplastic and destructurized have chain scissioning (hydrolysis) events occurring under T and P. Processing of Starch

9. Extrusion of Starch Extrusion is fast and continuous and the technology currently accepted by industry for the production of most commodity plastics., especially thermoplastics.Extrusion is fast and continuous and the technology currently accepted by industry for the production of most commodity plastics., especially thermoplastics.

10. Momentum, Mass, and Heat Transfer

11. Processing

12. Molecular Structure

14. Plasticized Starch

15. Plasticized Polymers If it is a high boiling point plasticizer like glycerol, it will stick around. The material is still useful and can be used to form soft, flexible parts.