1762
Cellulose (2017) 24:1759–1773
Afterwards the temperature was increased to 180 C for an additional 2 h. The composite was de-molded after cooling under pressure to room temperature. From the final composites, strips with dimensions of 40 9 5 mm 2 were cut with a lab paper cutter.
Nanopaper preparation
To avoid nanofibril aggregation, the CNF suspension was diluted to 0.8 wt% (105 mL, corresponding to a dry mass of 0.84 g) and mixed overnight using a magnetic stirrer. To this suspension, 2 wt% (based on CNF dry content) of water soluble polysaccharides OGG or GGM, respectively, were added and further stirred for 24 h to ensure homogeneity (Lucenius et al. 2014). Sequential filtering and pressing (O¨ sterberg et al. 2013) was used to prepare the CNF-WSPS nanopapers. CNF-nanopapers with grammages of 60 g m - 2 were prepared. Nanopapers from BC were prepared as previously reported (Mautner et al. 2015; Lee et al. 2012c). Briefly, the BC pellicles were first cut into small pieces (with a length of approximately 5–10 mm) and blended (Breville VBL065-01, Oldham, UK) for 2 min at a consistency of 0.2 wt% in deionized water to produce a homogeneous suspension of BC-in-water. These suspensions were then vacuum-filtered onto a cellulose filter paper (VWR 413, 5–13 l m pore size, Lutterworth, UK). The wet filter cake was wet-pressed under a weight of 10 kg between blotting papers (3MM Chr VWR, Lutterworth, UK) for 5 min to further remove excess water. These wet filter cakes were then consolidated and dried in a hot-press (25- 12-2H, Carver Inc., Wabash, USA) under a compres- sion weight of 1 t for 1 h at 120 C by sandwiching the wet filter cakes between fresh blotting papers and metal plates. BC-nanopapers with grammages of 50 g m - 2 were prepared.
Mechanical properties of the composites
Dynamic Mechanical Analysis of the composites was performed with a G2 RSA (TA Instruments, Eschborn, Germany) in three point bending mode. Specimens sized 40 9 5 mm 2 were cut from the composites and tested between - 50 and 250 C at 3 Cmin - 1 and a frequency of 1 Hz, an applied strain of 0.05% and a span distance of 25 mm. Tensile properties of the composites were deter- mined on at least five specimens for each material at 25 C and 50% RH using a 5969 Dual Column Universal Testing System (Instron, Darmstadt, Ger- many) equipped with a 1 kN load cell. The thickness of the composites was measured for each specimen before each test at ten different spots using a digital micrometer (705–1229, RS components, Corby, UK). The gauge length was 20 mm and the testing velocity 0.5 mmmin - 1 .
Morphology of the composites
The morphology of CNF-GGM composite films was studied using a high resolution scanning electron microscope (JEOL JSM-7500FA, Tokyo, Japan) in the Nanomicroscopy center at Aalto University and a Benchtop SEM (Jeol JCM-6000 Neoscope) in Vienna. The samples were freeze-dried in liquid nitrogen and fractured in half using tweezers while in the liquid nitrogen bath. Dust and loose particles were removed from the samples by blowing with nitrogen. A thin layer of gold/palladium (Emitech K100, Aalto) or gold only (JEOL JFC-1200 Fine Coater, Vienna) was sputtered on the sample surface to ensure sufficient electrical conductivity.
Preparation of nanopaper based composites
Composites were manufactured by laminating nanopapers with a two-component epoxy resin. Com- mercially available epoxy resin Araldite LY 556 plus 23 phr amine hardener XB 3473 were mixed and degassed under vacuum at 80 C for 10 min. Two nanopapers (diameter 120 mm) were laminated using a K Printing Proofer (RK PrintCoat Instruments Ltd, Hertfordshire, UK) at room temperature by applying a 50 l m layer of epoxy resin in between two nanopa- pers. After lamination the nanopaper-epoxy laminate was sandwiched between two Teflon films in a custom-made mold and placed into a hot-press. The hot-press was heated to 120 C. When reaching this temperature the sandwich was pressed at 2 t for 2 h.
Thermal degradation behavior of nanopapers and composites
The thermal degradation behavior of nanopapers and composites in nitrogen and air, respectively, was investigated using a high resolution modulated TGA (Discovery TGA, TA Instruments, Eschborn,
123
Made with FlippingBook - Online catalogs