K. E. Sykes

Publications (3)5.38 Total impact

• Article: Monitoring degradation of poly(hydroxybutyrate) by fracture toughness measurements

  J. K. Hobbs, K. E. Sykes, T. J. McMaster, P. J. Barham
  [show abstract] [hide abstract]
  ABSTRACT: The fracture behavior of poly(hydroxybutyrate) is described in terms of classical fracture mechanics. The fracture toughness (measured byG c, the strain energy release rate, andK c, the stress intensity factor) was monitored during physical aging and during chemical degradation with methylamine. A change in the measuredK c value was found after degradation by methylamine which does not seem to be due solely to the measured thickness changes. The work lays the foundation for studies monitoring changes in fracture behavior during environmental degradation.
  Journal of Polymers and the Environment 01/1996; 4(4):235-241. · 1.35 Impact Factor
• Article: Direct imaging of the surfaces of poly(β) hydroxybutyrate and hydroxybutyrate oligomers by atomic force microscopy

  K. E. Sykes, T. J. McMaster, M. J. Miles, P. A. Barker, P. J. Barham, D. Seebach, H. M. Müller, U. D. Lengweiler
  [show abstract] [hide abstract]
  ABSTRACT: Attempts have been made to image the fold surface of a single crystal of polyhydroxybutyrate (PHB) using the relatively new technique of atomic force microscopy (AFM). To overcome the obscuring of the fold surface by loose loops of polymer and chain ends, two different approaches were used. We first studied the single crystals of an oligomer of 32 HB units, which is known to fold once very tightly within a crystal, using AFM. Secondly, studies were made of single crystals of PHB which have been chemically degraded with methylamine to etch away the amorphous layer of loosely folded material, in an attempt to expose the fold surface. The crystals of the 32-mer had a similar morphology to those of the polymer PHB. However, at high magnification, lines of ridges were observed which ran parallel to the crystallographic b axis with a spacing of 0.7 nm, similar to the dimensions of the unit cell (0.58, 1.32, and 0.60 nm). It was not possible to differentiate between chain ends and folds. The partially etched PHB crystals maintained enough integrity to permit imaging by AFM, although surface detail could not be resolved on a molecular scale.
  Journal of Materials Science 12/1994; 30(3):623-627. · 2.02 Impact Factor
• Article: Morphology of single crystals of poly (hydroxybutyrate) and copolymers of hydroxybuty rate and hydroxyvalerate

  C. Birley, J. Briddon, K. E. Sykes, P. A. Barker, S. J. Organ, P. J. Barham
  [show abstract] [hide abstract]
  ABSTRACT: Single crystals of poly(hydroxybutyrate), and copolymers of hydroxybutyrate and hydroxyvalerate, have been grown from a variety of solvents and their morphology studied. In all cases the crystals appear elongated, with the crystallographic a axis along the long axis of the crystals. Screw dislocations (which act as branch points and can lead to large crystal aggregates) have been observed, and solvents, e.g. octanol in which more of these dislocations occur, have been identified. Decoration of the crystals with polyethylene shows that the fold plane is the (0 1 0) plane, while crystallographic and crystallinity arguments require successive adjacent folds to be along 1 1 0 directions. It is argued that folding is along [1 1 0] on the top, and [1 1 0] on the bottom surface of a crystal.
  Journal of Materials Science 12/1994; 30(3):633-638. · 2.02 Impact Factor