Revaluation of Guadua Fiber for the Sustainable Production of Recycled Thermoplastic Composites with Potential Industrial Applications and Their Corresponding Life Cycle Analysis

Abstract

Plastics are widely used in manufacturing various products due to their durability, strength, and low cost; however, they originate from nonrenewable sources. The growing interest in developing environmentally friendly materials has driven research toward the incorporation of natural fibers and recycled plastics. In Ecuador, Guadua Angustifolia Kunth (GaK) bamboo is usually used as furniture and construction materials. Therefore, this research work aims to reevaluate the traditional use of GaK fibers, exploring the potentiality of using chemically treated GaK fibers as reinforcement material for thermoplastic composites. This study presents the development of composite materials based on high-density polyethylene (HDPE), recycled HDPE (rHDPE), and treated GaK fibers, using an experimental design that includes performing tension, flexural, and impact tests to obtain an optimal composite material formulation. The composites were characterized using optical microscopy, SEM, FTIR, DSC, TGA, and EDX, followed by a life-cycle assessment (LCA). SEM images revealed morphological changes in the treated fibers, while TGA indicated significant mass loss due to degradation above 200 °C in all composites and DSC showed a melting temperature of approximately 133 °C for all samples. These results indicated there will not be significant GaK fiber degradation during processing. The highest maximum tensile strength achieved among all the optimization samples was 18.69 MPa. All composites showed an increase in Young's modulus, with enhancement up to 204% compared to pure HDPE, albeit with a marked reduction in elongation percentage. The maximum flexural strength increased to approximately 17.84%, but the impact strength decreased by 83% due to the low fiber-matrix compatibility and the low ductility of the composite, which allows it to absorb less energy before fracture. The optimal formulation had 10% cellulose, 50% HDPE, and 40% rHDPE, which exhibited a maximum tensile strength of 17.62 MPa, obtained from a mixture design regression. LCA demonstrated that rHDPE-based optimal formulation has a significantly lower environmental impact compared to virgin HDPE. Using rHDPE is critical for reducing the environmental footprint of composites, and incorporating GaK fibers further decreases GWP emissions while enhancing certain properties.

Figure 1

Composite material production diagram.

Figure 2

Ternary space and design.

Figure 3

System boundary for the production of plastic composites reinforced with GaK fibers.

Figure 4

Boxplots for stage 1.

Figure 5

Main effects plot for stage 1.

Figure 6

Boxplots for stage 2.

Figure 7

Main effects plot for stage 2.

Figure 8

GaK fiber comparison for stages 1 and 2 (30% fiber and 70% HDPE and rHDPE, equal parts).

Figure 9

ANOVA validation: (a) normal probability plot of residuals, (b) predicted vs actual (measured) responses, and (c) residuals distribution.

Figure 10

Effect plot (x1: Fiber, x2: HDPE, x3: rHDPE).

Figure 11

Contour ternary plot for results of optimization step (tones close to red are the highest values).

Figure 12

Characterized results for GaK-reinforced composites: (a) global warming potential, (b) terrestrial acidification, (c) freshwater eutrophication, (d) terrestrial ecotoxicity, (e) freshwater ecotoxicity, (f) marine ecotoxicity, (g) human carcinogenic toxicity, (h) human noncarcinogenic toxicity, (i) fossil resource scarcity, (j) process contribution to global warming potential, and (k) normalized results for optimal mixture sample 4 in the LCA evaluation.

Figure 13

SEM images of 5-year GaK fibers after hydrothermal and alkaline treatments and composite materials (first stage).

Figure 14

SEM images of young GaK fibers after hydrothermal and alkaline treatments and composite materials (second stage).

Figure 15

SEM images of the composite materials from the optimization stage.

Figure 16

Optical microscopy of the first stage composites.

Figure 17

Optical microscopy of the second stage composites.

Figure 18

Optical microscopy of the composites from the optimization stage.

Figure 19

FTIR spectrum of young and adult GaK fiber (after hydrothermal and alkaline treatment).

Figure 20

FTIR spectrum of HDPE, rHDPE, and first-stage composites.

Figure 21

FTIR spectrum of the second stage composites.

Figure 22

FTIR spectra of the composites from the optimization stage.

Figure 23

FTIR spectra of the composites from the optimization stage.