The chapter investigates the use of phenolic melamine polymer waste from the decorative paper industry as a raw material in gypsum mortars. Through experimental tests, it evaluates the properties of mortars containing different percentages of melamine waste, comparing them to standard gypsum mortars. The research highlights the potential of waste reuse in construction, focusing on the mechanical strength, water absorption, and adhesion properties of the resulting mortars. The study concludes with recommendations for future research, emphasizing the importance of sustainable waste management in the construction industry.
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Abstract
The proposed research studies the properties of gypsum mortars made with polymeric waste from the manufacturing process of high pressure laminated (HPL) thermosetting decorative panels, composed of cellulose paper layers impregnated with phenolic resins and melamine resins. The waste generated in the cutting, profiling and milling of the decorative panels is discarded and sent to landfill without a defined use. This research aims to contribute to the Circular Economy of Waste by recovering it as a raw material. Gypsum mortars are designed by adding different amounts of melamine waste. Subsequently, the properties of the mortars are studied following the technical prescriptions established in the European regulations. Firstly, the properties of the mortars in their fresh state are studied, such as the water/gypsum ratio, consistency, apparent density of the fresh mortar and setting time. Then, the properties of the hardened mortars are determined, such as the apparent density of the hardened mortar, mechanical resistance to bending and compression, adhesion, Shore C surface hardness and capillary absorption. Based on the results obtained in the tests, the viability of this type of waste is assessed for its use as a mineral aggregate to replace traditional aggregates, in order to obtain commercial gypsum mortars for use in masonry work, cladding, walls, or as a raw material for the manufacture of prefabricated materials. The results obtained show that the limit of gypsum substitution by melamine waste could be a maximum of 25%. New mortar formulations with lower substitutions would provide significant advantages in this type of ecological materials, in accordance with the technical requirements established by the applicable European regulations.
1 Introduction
In recent decades, the world's population has been increasing [1], a circumstance that will force an increase in industrial production to satisfy people's needs [2]. This situation can have an environmental impact due to the need to use larger quantities of raw materials in industry, and the inevitable production of the waste generated [3].
Faced with this situation, it is necessary to seek a reasonable balance between meeting the needs of the population and protecting the environment, in accordance with the Sustainable Development Goals (SDGs) [4]. Specifically, SDG 12 provides measures for companies to consume less energy reduce polluting emissions and make efficient use of natural resources [5]. To this end, they should focus on renewable energies and the circular economy of waste by incorporating more efficient technologies into their production systems, and the reuse and recovery of waste generated in manufacturing processes [5‐8].
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Construction is characterized as one of the economic sectors that uses the largest amount of raw materials of natural origin, many of which are non-renewable. It is also one of the industries that consumes the most primary energy for its transformation, and is responsible for the production of significant quantities of waste that are deposited in landfills without a defined use [9, 10]. For all these reasons, it is necessary to look for sustainable and environmentally friendly alternatives, such as, for example, recovering the waste generated in the industry for the design of new construction materials [11‐15]. In accordance with this objective, this document develops an investigation to assess the use of waste generated in the manufacturing process of decorative panels of cellulose paper impregnated with phenolic resins and melamine resins. Through experimental tests, we want to assess their suitability to be used as aggregates in the manufacture of gypsum mortars.
2 General Specification
The proposed research aims to valorize an industrial waste generated in the manufacturing process of decorative melamine panels, to use it as a raw material in the design of gypsum mortars for use in masonry.
2.1 Raw Materials
The following materials were used for the research:
Gypsum Type A1 composed of Hemi-hydrated Calcium Sulphate and Anhydrite, according to the specifications in EN 13279-1:2009 [16]. This type of gypsum has been provided by the company PLACO (Saint-Gobain Group). Its main characteristics are shown in Table 1.
Table 1.
Characteristics of the Type A1 plaster.
Characteristics
Reference
Particle size
0–0.2 mm
Bulk Density
0.810 kg/m3
CaSO4 content
>92.0%
Flexural Strength
>3.5 N/mm2
Compressive Strength
>3.0 N/mm2
Water/Gypsum Ratio
0.75 L/kg
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Melamine waste from the manufacturing process of decorative laminates for the coating of particleboard panels, composed of layers of cellulose paper impregnated with synthetic polymers of phenolic resins and melamine resins. The waste has been provided by the company Tacon Decor S.L., a manufacturer of laminates and decorative coatings, located in Burgos, Spain. The offcuts were crushed in a Retsch Model SM100 mill to obtain particles smaller than 2.00 mm, in order to facilitate their incorporation into the plaster matrix, with a bulk density of 0.724 kg/m3. (Figs. 1 and 2).
Fig. 1.
Melamine waste. General appearance by sizes (Left); Optical microscope visualization (Right)
Fig. 2.
Particle size distribution of ground melamine waste
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Water from the urban water supply of the city of Burgos (Spain), managed by Sociedad Municipal Aguas de Burgos, S.A.U.
2.2 Mortars Desing
The gypsum mortars made with melamine waste were designed by replacing, in volume, part of the plaster with crushed melamine waste, in order to check its effect on the properties of the dosed mixtures. Based on the reference mortar or standard mortar, made with A1 plaster, two mixtures were designed. The first is composed of 75.0% by volume of plaster and 25.0% by volume of melamine waste (75A1:25M) and the second of 50.0% plaster together with 50.0% melamine (50A1:50M). The dosage of the mixtures is shown in Table 2.
Table 2.
Dosage of the mixtures
Sample
A1 (gr)
Melamine (gr)
Water (gr)
w/g
A1
1000
-
500
0.500
75A1:25M
750
223.4
404
0.415
50A1:25M
500
446.9
360
0.380
At each dosage, the necessary water was added to achieve a run-out diameter of (160 ± 5) mm on the Flow Table Method, as specified in EN 13279-2:2014 [17]. For this purpose, the gypsum plaster and the melamine waste were first mixed dry and then the necessary amount of water was added for hydration of the gypsum plaster.
3 Experimental, Results and Discussion
The gypsum mortars made with melamine waste were analyzed both in the Fresh and Hardened State, according to the requirements of the EN standard (European Committee for Standardization - CEN). The following characterization tests were carried out:
3.1 Properties of the Mortars in the Fresh State
The density in the fresh state is calculated by difference of weights of a container of known volume, according to the standard UNE 102042:2014 [18]. For each of the designed mixes, the setting time is determined by the Vicat Cone Method [17], using a standardized probe of Ø 10 mm and 100 g weight, making several successive penetrations until a depth of about (22 ± 2) mm is reached (Fig. 3). The results are shown in Table 3.
Table 3.
Properties of mortars in Fresh State.
Sample
Water/binder
Density in the fresh state (kg/m3)
Initial setting time
(h:min:s)
A1
0.500
1714
0:07:23
75A1:25M
0.415
1620
0:07:30
50A1:50M
0.380
1450
0:07:30
Once melamine is added to the A1 gypsum, the mixtures obtained should be considered as a Type B1 gypsum, according to EN 13279-1:2009 [16]. For this reason, the water/gypsum ratio of mortars containing melamine is expressed as the ratio between the amount of water added and the weight of gypsum A1 plus melamine. Although, Table 3 shows that the w/g ratio decreases in mortars with melamine, Table 2 shows the amount of water dosed in each mix to obtain the design plastic consistency; part of this water is used to hydrate the gypsum and the rest to facilitate the sliding of the melamine aggregate particles on the gypsum matrix. On the other hand, due to the nature of the melamine waste, the mortars have a lower density. In terms of setting times, it should be noted that mortars with melamine waste behave similarly to standard A1 mortar.
3.2 Properties of the Mortars in the Hardened State
The flexural and compressive strength of the mortars was determined by the procedure of the standard EN 13279-2:2014 [17]. Table 4 shows the results obtained.
Table 4.
Properties of mortars in Hardened State.
Sample
Flexural strength
(N/mm2)
Compressive strength
(N/mm2)
Adherence (N/mm2)
Shore C hardness
A1
8.94
24.55
0.59
92
75A1:25M
4.65
12.35
0.43
90
50A1:50M
2.35
4.76
0.21
87
The results show that the mechanical flexural strength (Fig. 4) is reduced in the mixes incorporating the melamine waste with respect to the A1 reference mortar. As can be seen, each 25.0% of melamine added produces a reduction of the flexural strength by half (50.0%), with respect to the A1 standard mortar.
The mechanical compressive strength follows the same behavior (Table 4). When 25.0% melamine waste is added, the strength is also halved. However, when 50.0% is added, the reduction in mechanical strength is even greater, reaching 80.0% of that of the standard A1 gypsum mortar. If we consider the mechanical compressive strength as an indication of the quality of the material, the mixture (75A1:25M) allows a strength of 12.35 N/mm2 to be achieved, which is sufficient for many of the masonry works in which gypsum mortars are used. Finally, by applying the test procedure of EN 13279-2:2014 [17], the Shore C surface hardness was determined (Fig. 4). The results of the melamine mortars, although somewhat lower, are very similar to those of the standard A1 mortar (Table 4).
The adhesion of the mortars on a ceramic substrate also decreases as the content of melamine waste in the mixtures increases (Table 4). Replacing 25.0% of the gypsum with melamine reduces the adhesion by 27.0%, while in the case of mortar (50A1:50M) it reaches 64.5%. The type of fracture in the mortars is shown in Fig. 5. As can be seen, the five fractures in the standard A1 mortar are of the Adhesion Fracture (Type A) as specified in the standards. In the mortars made with melamine, four of the breaks are of the Adhesion Type and one of them is of the Cohesion Fracture (Type B), since part of the material remains adhered to the ceramic substrate.
The Coefficient of Water Absorption by Capillarity (Fig. 6), determined by standard EN 13279-2:2014 [17], is very similar in the three samples analyzed, being slightly higher in mortar A1 (Table 5).
Fig. 6.
Water absorption by capillarity (Left); Height of water (Right)
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However, the height that the water reaches after 10 min of testing is greater in the mortar (50A1:50M), probably because the melamine favors a more extensive capillary network in the mortar. Similarly, the Total Water Absorption is similar for A1 and (75A1:25M) mortars and higher for (50A1:50M) mortars.
Table 5.
Water absorption by capillarity
Sample
Absorption Coefficient
(kg/cm2min0.5)
Height of water
(cm)
Total Absorption (%)
(24 h)
(96 h)
A1
3.66
3.43
22.5
23.5
75A1:25M
3.17
3.31
22.9
23.6
50A1:50M
3.24
4.23
28.3
29.0
4 Conclusions
The research carried out shows a preliminary study to assess the possible use of melamine waste generated in the decorative paper manufacturing industry for particleboard panels. Mixtures of gypsum with melamine waste were designed and standardized test specimens were manufactured for testing, applying the procedures established by European regulations.
The tests carried out on mortars made with a 50.0% substitution of gypsum by melamine show a behavior that does not meet the regulatory requirements. However, mixtures with a 25.0% substitution show positive results, so that this substitution of gypsum for melamine could be considered as a maximum limit for future research with this type of waste. With this criterion, research could be reoriented by carrying out characterization studies with substitutions of less than 25.0% in order to establish the reference area in which it is possible to recover this waste with appropriate results to be used as a raw material for the manufacture of gypsum mortar for masonry.
Acknowledgements
We would like to thank the company Tacon Decor S.A. Burgos (Spain) for their collaboration in carrying out this research and the University of Burgos (Spain) for contributing to its financing.
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