Large datasets of water vapor sorption, mass diffusion immersed in water, hygroscopic expansion and mechanical properties of flax fibre/shape memory epoxy hygromorph composites

This data article presents four experimental sets of results related to flax fibre composites with epoxy shape memory polymer matrix: water vapor absorption, mass diffusion immersed in water, hygroscopic expansion, mechanical properties. The water vapor absorption tests are described in raw data related to four types of laminates with weights measured at different relative humidity (0%, 9%, 33%, 44%,75%, 85% and 100%). The mass diffusion experiments are related to weights of immersed samples over time. The unidirectional composite hygroscopic expansion is also measured along the fibre longitude and transverse directions. The mechanical properties of flax composite at various temperatures (20°C, 40°C, 60°C, 80°C and 100°C) and humidity environments (50% and immersed) are also described. Load-displacement diagrams of the hygromorph composites are converted into stress-strain diagrams via a compliance calibration, from which the tensile moduli are extracted. The data presented in this article can provide a benchmark for the development of new models, or for the determination of other properties via post processing. The detailed interpretation of the data can be found in [1]. The data is available in the Mendeley Data repository at [2].


Keywords:
Natural fibres Biocomposite Moisture absorption Hygroscopic expansion Mechanical testing measured along the fibre longitude and transverse directions. The mechanical properties of flax composite at various temperatures (20 °C, 40 °C, 60 °C, 80 °C and 100 °C) and humidity environments (50% and immersed) are also described. Load-displacement diagrams of the hygromorph composites are converted into stress-strain diagrams via a compliance calibration, from which the tensile moduli are extracted. The data presented in this article can provide a benchmark for the development of new models, or for the determination of other properties via post processing. The detailed interpretation of the data can be found in [1] . The data is available in the Mendeley Data repository at [2] .  , sodium chloride (NaCl), potassium chloride (KCl) and water. Those salts created RH conditions of 9%, 33%, 44%,75%, 85% and 100%, respectively. • Samples were stored for more than 48 hours in the specific relative humidity conditions. The samples were weighted with a balance with an accuracy of 10 −3 g.
Mass diffusion was measured as follows: • Four (4)  immersed in water. The weights of the samples over time have been measured using a balance with an accuracy of 10 −3 g. • The saturated samples have been dried at 50% RH, and the weights resulting in desorption measured over time in the same way followed for absorption.
The hygroscopic expansion has been measured in the following manner: • Samples consisted in unidirectional laminates [90 8 ].
( continued on next page ) The mechanical properties were measured in the following way: •

Value of the Data
• Natural fibres composites possess interesting mechanical properties, are relatively low-cost and environmentally friendly. These bio-based composites are moisture sensitive. It is therefore critical to understand their transport properties (water vapor sorption, mass diffusion), their hygroscopic expansion and the variation of the tensile Young's modulus at different thermal and humidity conditions. The knowledge of those characteristics can be used to design similar types of biocomposites, and/or benchmark classes of materials. Detailed datasets related to flax composites allow to generating high fidelity simulations of those composites and in general predicting and designing advanced biobased materials. • Researchers who study natural fibres composites properties affected by the humidity would benefit from the access to these data that allow to understand the moisture content of these biocomposites at different humidity levels, the hygroscopic expansion and variation of mechanical properties. • The datasets here is related to four experiments and quantities (sorption of moisture content, diffusivity, hygroscopic expansion ratio and Young's modulus). These materials metrics can be directly used in analytical and numerical models, also to benchmark other types of natural fibres composites. To the best of our knowledge, similar types and quality of data for biobased composites and hygromorph systems are not completely available in open literature.

Data Description
The file names are related to: 1-Water Vapor Sorption, 2-Mass diffusion, 3-Hygroscopic Expansion and 4-Tensile Property.

1-Water Vapor Sorption
The water vapor sorption file contains two files: the original weights of the samples at various RH conditions (named 'weight') and the moisture content at different RH percentages ('moisture content').

2-Mass Diffusion
The mass diffusion section contains six files: three of them are referred to the original weights of the immersed samples over time for the 1 st and 10 th cycle absorptions and the 10 th cycle desorption, respectively. The files are named '1st_absorb_weight', '10th_ absorb_weight', and '10th_desorb_weight'. The other three files contain data about the moisture content over time ('analysis_1stcycle_absorb_massdiffusion', 'analysis_10thcycle_absorb_massdiffusion' and 'analysis_10thcycle_desorb_massdiffusion').
• Column 2 to end Column: weights of samples at over time. The unit is mg.
• Column 2 to end Column: moisture content of samples at over time. The unit is %.

3-Hygroscopic Expansion
The hygroscopic expansion section contains two files. One is related to the 7 samples original weights, lengths, and widths when they absorb moisture (named 'length and width'). The other is referred to the hygroscopic expansion with different moisture contents (named 'longitude and transverse expansion').
The data structure of the 'length and width' files is the following: • Column 1 to 5 are: weights of samples (g), length of two positions and width of two positions (mm).

4-Tensile Properties
The tensile properties section contains three parts: the 'force-displacement' and the 'strainstress' folders, and the 'Tensile modulus' file.

Experimental Design, Materials and Methods
• Material supplier and processing Unidirectional flax fibre tapes (50 g/m 2 ) have been supplied by Nat-up, France. The flax fibres are fixed by tape on their boundaries and cut into a 250mm * 250mm size. Stacks of shape memory epoxy films [3] and unidirectional flax-fibre tapes have been cured in autoclave at 0.69MPa pressure with the following temperature profile: 80 °C for 3 hours, 100 °C for 3 hours and 150 °C • Water vapor sorption Samples have been stored in a reference condition within a vacuum oven at 60 °C, assumed to be close to 0% RH humidity [4] . During the experiments the samples have been stored in boxes with relative humidity controlled by saturated solutions of potassium hydroxide (KOH), magnesium chloride (MgCl 2 ), potassium carbonate (K 2 CO 3 ), sodium chloride (NaCl), potassium chloride (KCl). The salts allowed to reach RH values of 9%, 33%, 44%,75%, 85% and 100%, respectively. The samples were then weighed using a balance with an accuracy of 10 −3 g after reaching saturation, i.e., when the weight was stabilized. A period of 48 hours has been considered acceptable to reach the stabilization of the weight.
• Mass diffusion Samples have been initially stored at 50% RH and 23 °C to attain the reference state. The materials were then immersed in deionized water at room temperature. During immersion, the samples have been periodically removed to be weighed using a balance with an accuracy of 10 −3 g, and then characterized: In (1), W t and W 0 are the weight of the sample at a time t after water exposure and the weight of the dry material before immersion (for RH = 50% and T = 23 °C).
• Hygroscopic expansion Volumetric measurements [4] have been performed with a Mitutoyo micrometre IP65 (10 −3 mm). The gravimetric analyses have been made using a Fischer Scientific PAS214C balance (10 −3 g). The coefficient of hygroscopic expansion ( β) has been determined as the slope of the hygroscopic expansion over the moisture content .
In (2), L c and L 0 are the sizes of the sample at a time t after water exposure and before immersion, respectively .
• Elastic properties Tensile properties of dry (50% RH) and wet (immersed) unidirectional biocomposites with flax fibres orientations at 0 °(E L ) and 90 °(E T ) have been measured according to the ISO 527-4 standards by using a Shimadzu universal testing machine (cell load 5 kN) at controlled temperature (23 °C) with a crosshead speed of 1 mm/min. The samples had the following dimensions: t 0 °= 0.56 mm and width w 0 °= 15 mm; t 90 °= 0.56mm and w 90 °= 25 mm. The tests were performed on samples that reached the saturation state. The samples were covered with saran wrap to prevent the loss of moisture. A heating chamber (TCE-N300A, Shimadzu, UK) to control the setting temperature and thermocouples (621-2170 from RS components, UK) were also used to verify the temperature close to the samples. An axial extensometer (560S Shimadzu, UK) with a nominal length of 25 mm (L 0 ) was used to measure the strain.

Ethics Statements
This work has not involved any use of human subjects and animal experiments.

Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data Availability
Large datasets of water vapor sorption, mass diffusion immersed in water, hygroscopic expansion and mechanical properties of flax fibre/ shape memory epoxy hygromorph composites (Original data) (Mendeley Data).