دانلود رایگان مقاله پایداری حرارتی پراکندگی نانوسلولز

Abstract

Cellulose nanofibrils (CNF) have potential as rheology modifiers of water based fluids, e.g. drilling fluids for use in oil wells or as additives in injection water for enhanced oil recovery (EOR). The temperature in oil wells can be high (>100 °C), and the retention time long; days for drilling fluids and months for EOR fluids. Hence, it is important to assess the temperature stability over time of nanocellulose dispersions to clarify their suitability as rheology modifiers of water based fluids at such harsh conditions. Dispersions of CNF produced mechanically, by using TEMPO mediated oxidation and by using carboxymethylation as pretreatment, in addition to cellulose nanocrystals (CNC), have been subjected to heat aging. Temperature stability was best for CNC and for mechanically produced CNF that were stable after heating to 140 °C for three days. The effect of additives was evaluated; cesium formate and sodium formate increased the temperature stability of the dispersions, while there was no effect of using phosphate buffer.

4. Conclusions

Thermostability of dispersions of the nanocelluloses Mech-CNF, TEMPO-CNF, Carboxy-CNF and CNC, have been studied by heat aging at temperatures ranging from 110 to 150 ◦C. Additives that either stabilize pH or act as radical scavengers have been used in order to shed light over the degradation mechanisms. The results indicate that ORD is the main mechanism as addition of the radical scavengers cesium formate or sodium formate reduced thermal degradation considerably. The analyzes show clearly that the nanocelluloses start to degrade already at 110 ◦C, which is at a much lower temperature compared to experiments described in literature performed in dry state. Comparison of the nanocelluloses showed that there are differences between the nanocellulose qualities tested; Mech-CNF and CNC were the most stable qualities, being stable after heat aging to 140 ◦C for three days when using formate as additive. All the nanocelluloses assessed in this study had better temperature stability than guar gum and xanthan, which indicates that nanocelluloses show promise as rheology modifiers for drilling fluids in oil wells.