RESUMEN
Cellulose acetate butyrate (CAB) is a possible candidate, being a raw material derived from renewable resources, to replace fossil-based materials. This is due to its thermoplastic properties and the relative ease with which it could be implemented within the existing industry. With a significant amount of variation in CAB on the market today, a knowledge gap has been identified regarding the understanding of the polymer structural arrangement in films. This relates to the underlying mechanisms that regulate CAB film material properties, insights that are important in product development. In this study, commercially available CAB was investigated with XRD, SEM, AFM, and TOPEM DSC in order to obtain physicochemical information related to its micro-structural features in solvent-cast films. The film-forming ability relates mostly to the number of hydroxyl groups, and the semi-crystallinity of the films depends on the type and position of the side groups along the cellulose backbone. The appearance of signs of possible cholesteric ordering in the films could be connected to higher amounts of hydroxyl groups along the backbone that disturb the helix arrangement, while the overall order was primarily related to the butyrate substitution and secondarily related to the molecular weight of the particular CAB studied. Cold crystallization was also observed in one CAB sample.
RESUMEN
BACKGROUND: Previous publications have suggested a high correlation between flash visual evoked potential (F-VEP) N2 peak latency and intracranial pressure. This would enable F-VEP to be used as a non-invasive and inexpensive method to estimate ICP in a number of settings. However, basic knowledge about variability across subjects and test-retest properties of the F-VEP is lacking. METHODS: Fifteen healthy adult subjects were tested on three different occasions. F-VEP responses were recorded using international standards. FINDINGS: For the tested population, mean N2 latency was 65.7 ms (SD 10.7 ms) and the range was 48-110 ms. Intra-individual variability was high, in four of the 15 subjects more than 15 ms between testing sessions. The same was found for P2 latency and for N2 and P2 amplitudes. The response waveform was very variable and unambiguous marking of peaks was often difficult. One out of the 15 subjects had a very poorly developed F-VEP response, but a normal pattern-reversal VEP response. CONCLUSIONS: F-VEP has a wide range of latency, amplitude and waveform across normal subjects. A large proportion of subjects also had a high intra-individual variability over time. This variability makes F-VEPs unreliable as a marker for intracranial pressure, and caution in interpreting F-VEP changes in clinical work is advised.