Thermomechanical and microhardness data of melamine-formaldehyde-based self-healing resin film able to undergo reversible crosslinking via Diels-Alder reaction

The data presented in this article characterize the thermomechanical and microhardness properties of a novel melamine-formaldehyde resin (MF) intended for the use as a self-healing surface coating. The investigated MF resin is able to undergo reversible crosslinking via Diels Alder reactive groups. The microhardness data were obtained from nanoindentation measurements performed on solid resin film samples at different stages of the self-healing cycle. Thermomechanical analysis was performed under dynamic load conditions. The data provide supplemental material to the manuscript published by Urdl et al. 2020 (http://doi.org/10.1016/j.eurpolymj.2020.109601, [1]) on the self-healing performance of this resin, where a more thorough discussion on the preparation, the properties of this coating material and its application in impregnated paper-based decorative laminates can be found [1].

Material Science, Polymer Applied Science Specific subject area Self-Healing Melamine formaldehyde resin synthesis and properties Type of data Table  Graph How data were acquired Dynamic Load Thermomechanical Analysis (DL-TMA) Nanoindentation measurement Data format Raw Parameters for data collection A novel melamine-formaldehyde based resin surface film containing Diels Alder reactive functional groups was prepared and analyzed for its self-healing properties after damaging the film by scratching. The resin film was investigated as a cured solid resin film. Various heating cycles were covered by the applied temperature program. Description of data collection The cured MF-resin able to undergo self-healing due to Diels Alder functional groups was prepared as described in Urdl et al. 2020 [1] . The cured resin films were analyzed with DL-TMA and nanoindentation in order to characterize the mechanical performance of the MF resin when subjected to several self-healing cycles. Data source location Kompetenzzentrum Holz (Wood K plus), Sankt Veit an der Glan, Austria Data accessibility All raw data are available in this article.

Value of the Data
• The data allow a better understanding of the relationships described in the main paper and allow discussion of the properties of all investigated samples. They provide insight into the thermal-mechanical properties as well as the microhardness profiles of the produced melamine formaldehyde resin. It is important to understand the regeneration of its mechanical performance after undergoing several self-healing cycles. • Engineers and scientists who are working in the field of self-healing phenomena will be interested in these data, especially if they focus on the self-amending properties of thermosetting materials. The data are especially relevant to surface scientists, engineers who work in the field of coatings, laminates and engineered wood surface finishes. • The data can be compared to those of other resin films with self-healing properties and can be a reference for the development of resins formulations to be applied for laminate surfaces. • From the DL TMA measurements the shrinkage and expansion behavior of the self-healable MF resin is deduced. This indicates action of reversible or irreversible chemical reactions. Shrinkage indicates irreversible chemical reaction. A detailed discussion of the thermoanalytical data is found in [1] • From the nanoindenter profiles it is seen that the samples become increasingly stiffer as the number of self-healing cycles increases (i.e. the E modulus increases). A detailed discussion of the nanoindenter data is found in [1]

Data Description
Melamine-formaldehyde (MF) resins are duroplastic materials with good surface hardness, chemical stability and high transparency which makes them preferred surface finishing resins for paper-based decorative laminates [2] . Their excellent surface properties are due to their thermosetting character, which, on the other hand, is also responsible for the fact that self-healing of surface scratches is usually not possible with unmodified classic MF resins [3] . Recently, it has been shown that Diels Alder functional groups can be chemically integrated into melamine resin and that these groups are still reactive after condensation curing and can thermally crosslink reversibly [4][5][6] . It has also been shown that decorative laminates can be prepared with such DA modified resins that show self-healing activity when heated after being damaged by scratching [1] . The shown data are supplementary of the article Urdl et al. 2020 [1] . Figs. 1-10 show the dynamic load thermomechanical profiles of cured MF resin film subjected to various temperature programs. Fig. 11 (a, b, c, and d) shows nanoindentation measurements of different chemical stages (rDA and DA) of DA resin during the self-healing cycle of the resin. Fig. 12 (a, b, c, and d) shows the nanoindentation measurements of the stages of the rDA reaction.

Monomer preparation
Preparation of N 2 -(furan-2-ylmethyl)-1,3,5-Triazine-2,4,6-triamine (Fu-Mel) Monomer The Fu-Mel monomer was synthesized based on a method that was earlier presented by us [5 , 6] . 50 mmol of 2-aminomethyl furan (Fu), 48 mmol of 2-6-chloro-1,3,5-triazine-2,4-diamine (Mel), and 48 mmol of NaHCO 3 were combined with 40 mL of deionized H 2 O and 55 mL of EtOH. The reaction mixture was heated to 85 °C and kept at this temperature for 8.5 h. After the reaction was finished, EtOH was evaporated by applying vacuum. The reaction product had formed a yellowish precipitate. It was filtered from the aqueous solution and thoroughly washed with deionized water. The final reaction product was dried under vacuum overnight. No further purification procedure was applied to the Fu-Mel monomer. It was subsequently used for chemical transformation.
Preparation of monomeric Diels-Alder Adduct The Diels-Alder reaction between Fu-Mel monomer and BMI to give the monomeric DA adduct was carried out using the basic procedure described in research papers published earlier on the synthesis of Fu-Mel-based particles [5 , 6] . 9 mmol BMI and 18 mmol Fu-Mel were dissolved in a total volume of 35 mL of dimethylformamide. The reaction solution was stirred and kept under N 2 for 26 h at a constant reaction temperature of 60 °C.

Polymer Preparation
Preparation of the DA-Pre-Polymer used for Diels-Alder Resin Synthesis Preparation of the pre-polymer was performed as follows: 2 or 4 equivalents of formaldehyde were added to the DA adduct in dimethylformamide. The mixture was thoroughly mixed and kept at a reaction temperature of 70 °C. The reaction time was 40 min. The pre-polymer was dried at 65 °C for 12 h after synthesis.
Curing of DA Resin Curing of the resin samples was brought about in a hot-press. The pre-polymer was hot pressed in a SUT-PUK 1600 laboratory press (Svoboda Umformtechnik GmbH, Vienna, Austria). A high gloss pressing plate was applied in the pressing step to provide for smooth surface appearance. Pressing was done at a constant pressure of 20 N cm −2 . All samples subjected to a temperature profile consisting of four phases: (1) Heating phase with a temperature gradient from 65 to 120 °C within 200 s, (2) isothermal phase at 120 °C for 300 s, (3) cooling phase with a temperature gradient from 120 °C to 65 °C within 200 s, and (4) isothermal phase at 65 °C for 900 s.

Characterization of DA resin
Dynamic Load Thermomechanical Analysis (DL-TMA) DL-TMA was applied to characterize the curing state of the DA resin. A circular sample (diameter: 3 mm 2 ) was punched and analysed applying a dilatometric mode with an oscillating force ranging from 0.1 to 0.5 N in a rectangular mode with a time period of 12 s. The temperature programme was selected such as to cover several heating cycles. Heating rate was maintained at 3 °C min −1 . The detailed temperature programmes applied during the DL-TMA measurement procedure for the various samples were as follows: Sample DA01: (a) temperature rise from 30 to 80 °C using a heating rate of + 3 °C min −1 , (b) temperature drop from 80 to 60 °C using a cooling rate of -3 °C min −1 , (c) isothermal phase at 60 °C for a time period of 20 min, (d) temperature drop from 60 to 30 °C using a cooling rate of-3 °C min −1 ). This was repeated twice. Sample DA02: (a) temperature rise from 30 to 80 °C using a heating rate of + 3 °C min −  The upper, middle and lower envelope regard the range of elongation the material experiences during the dynamic load experiments. "Lower envelope" regards the lowest values measured for the dimension of the tested specimen in dependence of temperature during the dynamic load experiment, "high" envelope regards the largest values. "Middle envelope" represents the average dimension during the test in dependence of temperature and is, therefore, also called the "average change in elongation". Nanoindentation Measurements A UNHT 3 nanoindenter (Anton Paar, Graz, Austria) was used to characterize the cured DA resin. The device was equipped with a sphero-conical intender tip (100 μm, 90 °). All measurements were performed at room temperature. Measurements were done by applying a sinus on load mode with a constant strain rate to a maximum of 40 mN, a pause of 10 s, sinus frequency of 5 Hz and amplitude of 4 mN. Sinus on hold measurements were performed in a 2 × 2 matrix acquiring 4 measurements at a constant strain with a maximum load of 20 mN, a pause of 30 s and a sinus pause of 30 s with 1 Hz and 2 mN. The stiffness threshold was set to 150 μN μm −1 . The approach distance to 3 μm and speed to 2 μm min −1 . The static Young's modulus was determined in phase 2 of the measurement under constant force using equation (1) : In equation (1) , σ means the mechanical stress acting on the specimen, expressed as the effective force F per area A , and ε means the strain or relative change in dimension L induced in the sample in relation to its initial length ( L 0 ).
By applying a sinusoidal indentation stress under a constantly high load force, the nanoindentation measurement is operated in a mode that corresponds to a dynamic mechanical analysis. Thus, the loss factor, tan δ, can be determined from the frequency dependent modulus E IT .
For this, the following relationships were used: where E IT denotes the frequency dependent modulus, E storage the storage modulus, i.e. the ability of the material to absorb energy, and E loss the loss modulus.
To measure different healing stages during the temperature treatment in the self-healing process, the DA resin was tempered at 120 °C for 5 min, then rapidly cooled down to room temperature to freeze the rDA state, and subsequently measured. Afterwards, the sample was again tempered at 60 °C in the oven in order to support DA reaction. Thereafter, the sample was measured again. The described procedure was repeated three times to measure the material properties during three heating (i.e., healing) cycles.