Potentialities of Cellulose Nanofibers (CNF) in Low Density Polyethylene (LDPE) Composites

doi:10.21203/rs.3.rs-2869949/v1

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Potentialities of Cellulose Nanofibers (CNF) in Low Density Polyethylene (LDPE) Composites

https://doi.org/10.21203/rs.3.rs-2869949/v1

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The growing demand for polymeric materials makes them significant in both industry and the environment, and the task of making them sustainable is becoming increasingly challenging. Cellulose presents an opportunity to minimize the effect of non-degradable materials. Cellulose nanofiber (CNF) is part of a class of cellulose fibers with superior performance due to its high strength and stiffness combined with low weight and biodegradability. This work aimed to produce composites using Low Density Polyethylene (LDPE) as matrix and CNF from Pinus sp. (Pinus) and Eucalyptus sp. (Eucalyptus) as reinforcement. The CNF were obtained by mechanical defibrillation of the cellulose, subsequently the water was removed by centrifugation to then produce a master with CNF and LDPE using a thermokinetic homogenizer. The master was milled and blended with LDPE to obtain booster concentrations of 1, 2 and 3 percent by weight (wt. %). To characterize the composite, tensile and flexural tests, thermal and rheological analysis were performed. As a result, an increase of between 3 and 4% in the crystallinity of the composite was evidenced with the addition of Pinus CNF and a reduction of 2 to 3% in the crystallinity index with the addition of Eucalyptus CNF. Thermal stability increased for all compositions. For mechanical properties, increasing the CNF content increased the stiffness and tensile strength. In general, it was found that the process is an effective alternative to produce composites of LDPE with cellulose nanofibers.

Polymers

nanotechnology

composites

Currently, it’s important to promote the development of materials that employ renewable raw materials and that have a low environmental impact. Cellulose is the main component of the plants cell wall, representing the most abundant renewable polymer in the world. The advancement of the insight into the structural characteristics of cellulose has driven the creation of new types of materials, which create an opportunity in the future to minimize the effect of non-degradable materials by using it as reinforcement in thermoplastic matrices (Omran et al. 2021).

Cellulose fibers with at least one nanoscale dimension are called cellulose nanofiber (Nechyporchuk et al. 2016). With properties distinct from molecular cellulose and wood pulp, CNF are being developed for applications that were previously not possible for cellulosic materials due to the unique combination of characteristics (e.g., mechanical properties, sustainability, and large-scale production potential) and utility in a broad spectrum of material applications (Moon et al. 2016).

Low-density polyethylene (LDPE) has lower density and greater flexibility than other types of polyethylene, making it ideal for a variety of applications. As the polymer industry becomes more receptive to the use of wood-based fillers, more effort is needed to improve the properties of these materials. New materials must be constantly evolving their intrinsic properties, seeking increasingly affordable costs, as is the case with natural fiber composites, making them attractive for various applications (Agnes et al. 2020).

New business niches need to be reinvented in response to the rapid changes and developments in the modern world. One of these demands deals with the sustainable use of plastic packaging and parts, where the industry faces challenges related to non-degradable product materials. This issue requires all stakeholders in this industry to seek alternatives to overcome the related problems (Abdul Khalil et al. 2016). In the field of three-dimensional (3D) printing, composites are increasingly entering the fused deposition modeling (FDM) market. With a limited number of publications, LDPE is a less common material in the 3D printing industry, with fewer studies and research conducted on its properties and applicability in the printing process. This study can offer several opportunities for technological innovation as fillers in the form of natural fibers are convenient: they have the possibility to reduce costs while maintaining the characteristics of the filament, as well as allowing the development of more sustainable solutions (Blanco, 2020).

In the perspective of innovation in the area of composites, this work aimed to evaluate the potential of blending CNF with LDPE. For this, two types of CNF were used, varying their concentrations in the polymeric matrix, to test the hypothesis of gains in the formulations in mechanical, thermal and rheological properties.

2.1. Materials

To make the composites, bleached pulps from Pinus sp. (Pinus) and Eucalyptus sp. (Eucalyptus) were used. Both pulps came from chemical production processes. From this material it was possible to produce the CNF. Braskem S.A. brand LDPE (variation EB853/72 SPWAGK049E) with flow rate 2.7 g/ 10 min and density 0.92 g/cm³ was used in the matrix phase of the composites.

To evaluate the composites produced with different characteristics and relate them to the evaluated properties, specimens were produced varying the type of CNF reinforcement and the proportion matrix-reinforcement in two production systems: injected specimens and FDM printed specimens. The experimental model is presented in Table 1.

Table 1

Experimental model
Composites	Production System	CNF	Proportions (wt. %)
Composites	Production System	CNF	CNF	LDPE
1	Injection	Pinus	1	99
2			2	98
3			3	97
4		Eucalyptus	1	99
5			2	98
6			3	97
7		-	-	100
8	FDM	Pinus	1	99
9		Eucalyptus	1	99
10		-	-	100

The proportion of CNF was limited to 1% for FDM because adding CNF in larger amounts could increase the viscosity of the polymer, which could lead to problems in extrusion, such as nozzle blockages or variations in layer thickness, making it more difficult to mold and process.

2.2. Obtaining cellulose nanofibers (CNF)

For CNF production we adopted the mechanical defibrillation method in a high shear mill (Super Masscolloider MKCA6-2 brand Masuko®), adapted to a recirculation pump.

Previously, the Pinus and Eucalyptus pulp sheets were chopped and dispersed in 5 liters of distilled water, at a concentration of 5% m/v, to allow fibrillation of the maximum volume of CNF without agglomeration of solids in the recirculation pump. The pulp was subjected to a process in which it was pressed between a stationary grinding stone and another one rotating around 1500 rpm, resulting in the separation of the CNF that form the cell wall. The pulp was circulated between the stones for 5 hours, a standard time known and defined in the laboratory, with the aid of a recirculation pump until it reached the texture of a gel.

To maximize the CNF content and reduce the moisture content of the gel to favor the subsequent steps, the solution obtained from the mill was centrifuged under a speed of 6000 rpm for 5 minutes at 60 seconds acceleration and braking to remove excess water from the gel. The moisture content of the gel was calculated to ascertain the actual concentration of CNF before mixing it into the matrix.

2.3. Preparation of CNF/LDPE composites

To circumvent the effects of moisture on the composite and facilitate the impregnation of CNF by LDPE, a premix was carried out in a Thermokinetic Homogenizer - "Drais" composed of 70g of CNF and 15g of LDPE granules.

First the LDPE was added in the mixing chamber, then the equipment was activated at 120 ºC. At the beginning of the melting process, the CNF was added, and it remained in the melting process for 5 minutes under a temperature of 160 ºC.

At the end of the process a masterbatch was obtained, with an excess concentration of fibrous reinforcement so that it can be used in masterbatch dilution in the next extrusion process. The composites were processed in an interpenetrating and co-rotating twin-screw extruder (MH Equipamentos, model MH-COR-20-32). The temperature profile used had a range from 77 to 240°C from feed to output, being respectively 77 ºC, 153 ºC, 190 ºC, 185 ºC, 190 ºC, 195 ºC, 200 ºC, 190 ºC, 200 ºC, 240 ºC. With a screw rotation speed of 200 rpm and length to diameter ratio (L/D) = 46. After the end of the process, the granulated material was dried in an oven at 80 ºC for 12 hours.

2.4. Production of CNF/LDPE injected specimens

The injected specimens were produced in a Himaco 150 − 80 device model LHS 150 − 80, at temperatures ranging from 185 to 200°C, under a rotational speed of 100 rpm and pressure of 650 bar for 4 seconds. The mold cooling time was 45 seconds, and the exit mold temperature was approximately 20°C. Specimens were produced for tensile (ISO-527/12, type I) and flexural (ISO-178/10) mechanical testing.

2.5. Production of Filaments for Use in 3D Printer

The filaments for 3D printer feeding were produced with a prototype laboratory mini-scale extrusion line which can operate with outputs ranging from 30 g/h to 300 g/h. The extrusion line is composed of a co-rotating twin-screw extruder (screw diameter D = 13 mm, L/D of 27) with five heating zones, coupled to a die with a 3 mm hole diameter for filament extrusion, and an extraction and cooling unit composed of a water trough, where the filament is cooled, and a speed-controlled roller. For all the compositions, the temperature profile was 200 ºC/200 ºC/200 ºC/210 ºC/200 ºC, and filament die at 210 ºC, whereas the extrusion speed was 80 RPM. Due to the higher expected stiffness of the composite, the extrusion process to produce filaments with NFC composite materials needed to be slower to prevent material breakage and ensure that the desired properties were maintained. When a material is stiffer, it can be more difficult to extrude into a uniform filament, which can lead to quality issues such as variations in filament thickness or breaks in extrusion. At the start of processing, each of the three treatments required a particular combination of material feed into the hopper being 300 g/h for LDPE and 280 g/h for composites, the speed of pull to achieve the optimum diameter of 1.75 mm was 10.6 RPM for LDPE and 9.3 RPM for composites.

2.6. Printing of specimens by FDM

The production of the specimens was carried out in a RAISE 3D Printer Pro2 Series. Not having much information related to LDPE printing, tests were performed to determine the best conditions for printing. The printing process settings for all filaments were: layer height of 0.4 mm, flow rate of 80%, nozzle temperature of 200°C, and printing speed of the first layer 1 mm/sec. The speed of the other layers was 2 mm/s for the composites and 1 mm/s for the LDPE.

By means of the FDM technique specimens were produced for mechanical tensile testing. The fabrication of the specimens followed the determinations of the ISO-527/12 standard, being type I. The impression deposition occurred at 0º.

2.7. Composite characterization

The characterizations performed in this work were: tensile and flexural strength of injected composites, tensile strength of FDM printed composites, thermal and rheological analysis for the pellet composite.

2.7.1. Tensile and flexural strength

Five specimens were tested for each injected treatment and five specimens for each 3D printing molded treatment, following ISO-527/12, type I, which standardizes the dimensions and conditions. Tensile tests were performed at a speed of 5 mm/min until rupture, determining stress at maximum strength and modulus of elasticity.

The bending test was performed according to the standard ISO-178/10. The tests were performed at a speed of 5 mm/min. Four specimens of each injected treatment were tested.

2.7.2. Thermal analysis

The thermal properties of the composites and crystallinity index were obtained by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA samples with a mass of approximately 12 mg were subjected to a flow rate of 50 ml/min, starting from room temperature at 25°C to reach 710°C at a heating rate of 10°C/min. DSC analysis was performed under the same conditions, with heating up to 320°C, followed by cooling.

2.7.3. Rheology

The flow curves of the materials were measured during filament extrusion, enabling in-line rheological analyses without interrupting the production process by means of a double-slit rheometrical die coupled to the laboratory mini-extruder, as detailed elsewhere (Teixeira et al. 2018). This experimental approach is specifically suited to the rheological characterization of thermosensitive materials such as biodegradable composites (Teixeira et al. 2020), as it allows by-passing an additional thermal cycle linked to the preparation of samples for rotational or capillary rheometry.

The determination of a flow curve was performed at constant feed rate and screw speed. For each data point, a given opening combination of the measuring and the filament production channels is achieved by rotating valves located at the entrance of the respective channels. This allows balancing the material flow in both channels whereas the pressure at the outlet of the extruder is maintained constant. Both material output and pressure drop in the measuring channel were recorded after reaching steady state. Each successive point of the flow curve was obtained for another opening combination of the valves while the pressure at the extruder’s outlet is maintained at the same constant value. The calculations to convert material output and pressure drop into shear rate and shear stress rely on equations developed for slit rheometry as detailed elsewhere (Teixeira et al. (2018)).

3.1. Thermal analysis

Figure 1 shows the thermogravimetry (TGA) and derivative (DTG) curves of the composites with Pinus CNF and Eucalyptus CNF, as well as the LDPE matrix.

For the composites, two events can be observed in TGAS curves. The first one refers to the degradation of CNF in the temperature range between 284 and 362 ºC, where there was a small weight reduction between 0.5 and 2.5%, which was expected considering the low content of CNF. The second event pertains to the degradation of LDPE, above 465°C. It’s observed that due to the centrifugation and embedding process, as well as the low CNF content, no weight variation due to water loss can be observed. Heating of the composites shows a broad, somewhat noisy melting curve due to the relaxation processes in the sample.

Table 2 shows the weight percentages at maximum temperatures for the two identified degradation processes. There is a tendency for the thermal stability of the polymer to increase with the addition of CNF as the maximum temperature of the second event assigned to LDPE is shifted from 467 ºC to 476 ºC.

This occurs due to the presence of incorporated CNF that serves as a barrier to degradation.

Ferrer et al. (2016), in a study with CNF/polyolefin blend, observed that the composites slightly reduced thermal stability with the CNF content varying from 1 to 3 wt. %, explained by residual cell wall components, different from cellulose and lignin, present in the fibers.

Table 2

Thermogravimetric analysis of composites with Pinus CNF, Eucalyptus CNF, and LDPE
	First Event		Second event		Residual weight (%)
Composition (wt. %)	T Max (ºC)	Weight loss (%)	T Max (ºC)	Weight loss (%)	Residual weight (%)
LDPE	-	-	467	66,27	1,65
LDPE/ Pinus CNF 1%	351	0,29	469	67,59	2,12
LDPE/ Pinus CNF 2%.	356	0,46	471	61,33	2,54
LDPE/ Pinus CNF 3%.	357	1,34	476	65,93	1,38
LDPE/ Eucalyptus CNF 1%.	284	0,46	475	70,77	0,2
LDPE/ Eucalyptus CNF 2%.	355	0,46	470	67,04	2,8
LDPE/ Eucalyptus CNF 3%.	362	2,48	474,1	74,63	0,83

The difference in burn residue values between pure LDPE and LDPE composites with CNF suggests the occurrence of chemical reactions between the LDPE and CNF during processing or burning of the material. Volatilization of products may indicate the release of gases resulting from chemical reactions between the components of the composite, which may include the breaking of chemical bonds and the formation of new products. The weight loss in the first event is an indication of the release of volatiles, pine NFC volatilizes less than eucalyptus NFC.

Figure 2 shows the DSC curves for the LDPE and the composites recorded during the first heating and subsequent cooling. Note here that the first heating for DSC relates to crystallinity since glass transition processes cannot be probed within the temperature range accessed.

It was found that CNF addition shifted the melting temperatures to higher values than for the neat LDPE. Due to the small proportion of reinforcement to LDPE, the variations in thermal properties did not produce a marked effect, reflected in the phenomena dependent on thermal stability. The DSC curves obtained for the pure matrix as well as for all composites were conventional and similar, characteristic of semicrystalline materials (Oliveira de Castro et al. 2015).

During cooling, a transition near 60°C was observed, related to the relaxation of LDPE after crystallization. The LDPE showed onset of movement in the chain segments around 60°C, which is said to be the glass transition temperature (Tg). The composites showed Tg in the range of 57 to 60°C. The blends exhibited higher crystallinity and higher Melting temperature (Tm) compared to LDPE.

From the DSC curves, data was obtained for the interpretation of the thermal events, which are presented in Table 3.

Table 3

Thermal properties of materials
Treatment (wt. %)	ΔHm (J/g)	ΔHc (J/g)	MT (ºC)	%C
LDPE	163,83	96,83	113,57	56%
LDPE/ Pinus CNF 1%.	169,60	124,78	115,17	59%
LDPE/ Pinus CNF 2%.	170,44	107,42	117,42	60%
LDPE/ Pinus CNF 3%	157,44	112,27	116,33	56%
LDPE/ Eucalyptus CNF 1%.	156,28	95,08	116,46	54%
LDPE/ Eucalyptus CNF 2%.	150,89	101,24	115,69	53%
LDPE/ Eucalyptus CNF 3%	149,16	154,51	115,24	53%

^{ΔHm: Melting Enthalpy; ΔHc : Crystallization Enthalpy; MT: Melting Temperature; %C: Degree of crystallization in %; ΔHm0 = 290J/g (Wunderlich, 2012)}.

The composites with Pinus CNF showed higher crystallinity than LDPE, while the composites with Eucalyptus CNF showed lower crystallinity than LDPE. The type of CNF affected the arrangement of the chains in the composite, the degree of crystallinity of a material is influenced by the ordered arrangement of its molecular chains, which in turn depends on the cooling rate during solidification. The slower the cooling, the more time the molecular chains must organize and align themselves to form a more ordered configuration. Since nucleation is the initial process of crystallization, it’s possible to conclude that the addition of Pinus CNF to LDPE works as a nucleating agent, promoting the organization of lamellae in the polymer structure, resulting in an increase in the degree of crystallinity compared to pure LDPE, indicating that the composite reinforced with Pinus CNF presented better interaction between the groups present in the chains, so that their alignment was better stabilized, compared to the composite reinforced with Eucalyptus CNF. The greater chain flexibility of the Eucalyptus CNF reinforcement corroborates this result. The kinetic factors that will be presented next also play an important role in the process, since the less rigid chains present in the Eucalyptus CNF reinforced composite may require considerable time for crystallization.

3.2. Rheology

Figure 3 shows the flow curves for composites with 1 wt.% of CNF selected for filament extrusion and 3D printing. As can be seen from the data presented, the processability of the LDPE matrix is affected by the addition of Eucalyptus nanofibers to the polymer. Whereas the incorporation of Pinus CNF has virtually no effect on the rheology of LDPE in the range of tested shear rates, the incorporation of Eucalyptus CNF leads to a drop in the shear viscosity. In contrast to this, the shear thinning behavior of the composites is essentially resembling the shear thinning exhibited by the LDPE matrix.

At low strain rates, the contribution of the cellulosic phase was shown to be more apparent. In another study with LDPE, the viscosity of matrices was higher compared to the addition of 10 wt. %, filler, also at low shear rates (Shumigin et al. 2011).

The addition of Eucalyptus CNF reinforcement to LDPE slightly reduces the viscoelastic range. This behavior can be attributed to the degree of polymer-reinforcement interaction, which requires lower shear stress and shorter relaxation times for the composites to flow. According to Han (2007), the relaxation of the dispersed phase itself is often longer than the relaxation of the polymer chains of the individual components.

The shear viscosity of the composite melts depends on the concentration, size, shape, distribution of the CNF in the matrix, and the physical-chemical interaction between matrix and CNF (Mariano et al. 2014). The presence of CNF disrupts the normal flow of the polymer and hinders the mobility of the chain segments. Ideally, the morphology of eucalyptus CNF, which is shorter in length than pine CNF, as cited by Lavoratti et al. (2016), performed under the same conditions and method, facilitates processability because the shorter the fiber, the better the dispersion of the material and the lower the resistance to deformation, thus reducing viscosity. The polymer chains are easier to orient and as a result can accelerate the flow. Thus, there is more shear thinning, which explains the lower viscosity of the matrix. Therefore, higher CNF content and length hinders the dispersion of the phase in the polymer and increases the viscosity of the loaded polymer. Based on the viscosity, adding 1 wt. % of CNF to the samples makes them stiffer for Pinus CNF compared to Eucalyptus CNF. The fact that we have a higher viscosity is due to the Pinus NFCs occupying a larger volume fraction than the eucalyptus fibers due to their size.

3.3. Flexural strength

Figures 4 and 5 show the averages of the flexural properties of the injected specimens, interpreted based on the values of modulus of rupture (MOR) and modulus of elasticity (MOE).

Except for the composite with 3 wt. % of Pinus CNF, all mixtures showed an increase in flexural strength properties. The increase in the proportion of CNF reduced the MOR for Pinus CNF and showed no significant difference for Eucalyptus CNF. The most flexural resistant composite was with 3 wt. % Eucalyptus CNF with 6.41 MPa and the lowest MOR value was observed in the composite with 3 wt. % of Pinus CNF, 4.93 MPa. According to English at al. (1997), increasing the content and length of fiber loading in the LDPE matrix results in stiffening of the composite materials and, therefore, a decrease in toughness and flexural strength is observed. The decrease in MOR of the composite compared to pure polymers may also be associated with the mechanical performance may be impaired due to the nature of the CNF. Lavoratti et al. (2016) observed that Eucalyptus CNF forms a more open network of fibrils, while Pinus CNF has a clumped formation, which limits the quality of CNF dispersion in the polymer matrix leading to lower mechanical strength values.

The MOE values increased both with addition of CNF reinforcement, as with the increment in the proportion for all composites. The composite with 3% Eucalyptus CNF (wt. %) showed the highest value also for stiffness, 155.22 MPa and the lowest value of MOE was observed in the composite with 2% Pinus CNF (wt. %), 126.07 MPa, still higher than LDPE. According to Ahmadi et al. (2017), the increase in composite stiffness is explained by the reinforcing action of CNF applied to LDPE. Due to the intrinsic stiffness of CNF, the storage modulus of the composites is higher than LDPE, indicating that stress is transferred from the matrix to the cellulose fibers. The filler particles restrict the deformation of the material.

With the increase of the reinforcement proportion, the samples become stiffer for Eucalyptus CNF in comparison to Pinus CNF. As presented, this agrees with the results for composite viscosity, since the composite with Eucalyptus CNF showed lower viscosity rates than the one reinforced with Pinus CNF. The lower viscosity of eucalyptus relates to a larger degree of orientation of CNF along the flow and also during injection. And more orientation results in larger flexural quality.

3.4. Tensile strength of injected specimens

At Figs. 6 and 7 the averages of the tensile properties for the samples produced by injection are presented, where the results for tension at maximum force (tension) and tensile modulus of elasticity (E) are evidenced.

The tensile strength increased for all treatments with the addition of CNF. The highest tensile strength was observed for the composite with 3 wt. % of Eucalyptus CNF, 11.45 MPa, while the lowest value was for the composite with 1 wt. % of Pinus CNF, 10.88 MPa, however, higher than the pure LDPE (10.53 MPa). The results are in agreement with the literature. Gray et al. (2018), when studying formulations injected with low loading of CNF + LDPE concludes that the best treatment was affected by 1 wt. % of CNF, achieving tensile strength of 8.6 MPa, lower than found here. Ahmadi et al. (2017) studied LDPE composite with CNF and observed that with increasing concentrations of CNF, the tensile strength of the composites was gradually increased, reaching the maximum values of 15.1 MPa for the composite containing 3 wt. % of CNF (wt. %). The mechanical properties of composites are related to the amount of CNF and the formation process.

With increasing CNF content, the E becomes higher in relation to LDPE indicating the reinforcing action of CNF. Such behavior is expected since, according to Marcovich et al. (2004), the modulus of a filled system depends on the properties of the two components, the filler and the matrix, therefore, the E of CNF, being greater than the E of LDPE, causes an increase in the elastic modulus of the composites. The increase in E of the composites relative to LDPE is also associated with the mobility restrictions of the macromolecules imposed by the presence of CNF.

In general, in the tensile test, the Eucalyptus CNF showed superiority to the Pinus, caused by the variation in size and formation of the CNF, the Eucalyptus CNF is shorter (Lavoratti et al. 2016) favoring the processability and encapsulation of the composite, associated with a better dispersion of the CNF in the matrix. Another corroborating factor is that the viscosity indexes of the Eucalyptus composite were lower, favoring the processing and consequently the mechanical quality of the composite produced.

3.5. Tensile strength of 3D printing specimens

The tensile properties of the FDM-produced composites are shown in Fig. 8 and Fig. 9. The highest values found for tensile strength and tensile modulus of elasticity were 9.15 and 114.33 MPa respectively. Compared to the results found for injected parts, the processing method is the main factor of interference in the mechanical properties of the composite.

An improvement in stiffness was observed with the addition of CNF to the polymer, indicating that the stress was transferred from the matrix to the cellulose nanofibers, which restrict deformation. The higher Mt of the composites favors the self-supporting characteristic of the part and decreases the effects of shrinkage and warping during printing facilitating the process.

As with the injected composites, with the addition of 1 wt. % of CNF filler, the samples make them stiffer for Pinus CNF compared to Eucalyptus CNF, based on the elasticity data serving as a measure of molecular stiffness this occurred due to the lower viscosity of the composite with 1 wt. % of Eucalyptus CNF, since viscosity is the "coefficient of rigidity" of the fluid to movement, the higher the viscosity, which hinders the fluidity of the material, the higher the modulus of elasticity and greater stiffness.

The composites with Eucalyptus CNF showed superior strength, also explained by the lower viscosity, since less viscous materials facilitate the processability of the material when printing the piece and consequently favor the mechanical quality of the final material.

The strength and stiffness are also affected by the levels of crystallinity (%) that significantly affect the properties of the polymers. The composite with 1 wt. % of Pinus CNF showed %C = 59%, higher than the composite with Eucalyptus CNF. According to Furukawa et al. (2006), polymers with higher crystallinity have higher glass transition temperature, i.e., they delay the relaxation of chains and last longer before reaching the elastomeric state and consequently have higher stiffness.

The printing speed doubled with the addition of CNF, 2 mm/s for the composites and 1 mm/s for LDPE. There are several factors that can influence the printing speed, in the specific case, the composite showed higher mechanical strength than LDPE, which may allow a higher printing speed without compromising the part quality.

It’s possible to produce LDPE polymer composites reinforced with CNF.

The composites with Pinus CNF showed higher crystallinity than LDPE.

In general, composites with 3% of CNF from eucalyptus showed superiority over that of Pinus NFC.

The addition of CNF improved the thermal stability of the composites.

The addition of Eucalyptus reinforcement to LDPE slightly reduces the linear viscoelastic range.

Overall, the results indicate that incorporation of CNF using the proposed method is an effective strategy, showing promising results for commercial applications.

The addition of CNF showed reinforcement action for both the injected specimens and the specimens produced by 3D printing. The mechanical properties of the composites did not show significant reductions, so it can be an alternative to reduce the use of polymer from nonrenewable source. The reinforcement improved the stiffness properties for all compositions.

The addition of NFC has doubled the print speed, increasing efficiency and reducing costs.

Acknowledgements: The author thanks the University of Caxias do Sul (Caxias do Sul, Brazil) and the University of Minho (Guimarães, Portugal) for their welcome and technical-scientific collaboration.

Funding: This work was carried out with the support of the Coordination for the Improvement of Higher Education Personnel - Brazil (CAPES) - Financing Code 001.

Conflicts of Interest: The authors declare no conflict of interest.

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No competing interests reported.

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Editorial decision: Revision requested
07 Aug, 2023
Editorial decision: Major revision
07 Aug, 2023
Reviews received at journal
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Reviewers agreed at journal
20 May, 2023
Reviewers agreed at journal
03 May, 2023
Reviewers invited by journal
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You are reading this latest preprint version

Potentialities of Cellulose Nanofibers (CNF) in Low Density Polyethylene (LDPE) Composites

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Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Materials

2.2. Obtaining cellulose nanofibers (CNF)

2.3. Preparation of CNF/LDPE composites

2.4. Production of CNF/LDPE injected specimens

2.5. Production of Filaments for Use in 3D Printer

2.6. Printing of specimens by FDM

2.7. Composite characterization

2.7.1. Tensile and flexural strength

2.7.2. Thermal analysis

2.7.3. Rheology

3. Results and discussion

3.1. Thermal analysis

3.2. Rheology

3.3. Flexural strength

3.4. Tensile strength of injected specimens

3.5. Tensile strength of 3D printing specimens

4. Conclusion

Declarations

References

Additional Declarations

Status:

Version 1