Research on the Whole Life Cycle of a Furniture Design and Development System Based on Sustainable Design Theory

Abstract

With the development of society, the negative impact of furniture waste on the environment has become increasingly prominent. Therefore, it has become essential to integrate sustainable design principles into furniture manufacturing. This integration can significantly extend the service life of furniture products and reduce the adverse impact on the environment. To achieve this goal, it is necessary to actively conduct market research and an in-depth understanding of users’ needs for sustainable furniture design. Among them, applying the AHP-QFD-AD method to develop a comprehensive design evaluation model is a practical way. This model can translate user requirements into explicit functional requirements and further refine them into specific design parameters. Accurately reflecting user needs in product design greatly improves the accuracy of design evaluation, thereby reducing environmental impact throughout the product life cycle. By implementing this integrated model, we can move furniture products in a sustainable direction. In addition, this method can also enhance the connection between the user and the product, extend the service life of the product, and reduce the waste of furniture. Using sustainable shelving development as an example, we validate the proposed method model. This study reduces the harm of discarded furniture to the environment, providing some support for sustainable furniture design practices.

1. Introduction

In the context of rapid economic growth, humanity’s resource demands have outstripped the Earth’s capacity to provide, creating a substantial ecological deficit [1]. This has given rise to various global challenges, including environmental degradation, climate change, energy scarcity, and other threats to human well-being and security [2]. In our rapidly evolving society, there is a growing recognition of the intricate link between social progress and environmental concerns. This realization has significantly magnified the importance of the “sustainable development concept” [3]. One noteworthy domain in which sustainable development is furniture design. The swift furniture turnover and the escalating disposal of outdated pieces pose considerable environmental hurdles [4]. To confront these challenges, it is imperative to embed sustainable design principles into furniture manufacturing. This entails strategizing and striving to prolong the lifespan of furniture items using recyclable materials.

The concept of sustainable design originated from the mid-20th century’s environmental movement and increased environmental consciousness. Over time, it has expanded to cover a wider range of fields and aspects. The evolution of sustainable design can be summarized through the following phases (Figure 1): In the initial phase, industrialization’s impact and consumption habits on the environment prompted designers to explore ways to reduce the environmental footprint, including eco-friendly materials and resources. The second stage emphasizes life cycle thinking as a central principle of sustainable design. Subsequently, ecodesign took the spotlight at the third stage, focusing on aligning with natural systems and emphasizing balance, circulation, and adaptability. As societal issues gained prominence, the fourth stage saw designers progressively integrate social sustainability considerations. Finally, in the fifth stage, the circular economy concept surged, prioritizing optimal resource utilization and recycling.

American economist Raymond Vernon put forward the product life cycle theory in 1966 [5]. This theory posits that products experience four core stages in the market: introduction, growth, maturity, and decline (Figure 2). Each step brings unique characteristics and market dynamics, requiring tailored strategies to navigate effectively.

The furniture whole life cycle theory considers environmental, social, and economic factors at all stages, from sourcing and design to manufacturing, distribution, use, maintenance, and disposal. Each phase contributes to sustainability and overall value. This theory emphasizes addressing impacts throughout furniture’s life cycle to promote sustainable development. Shelving, common household furniture, can benefit from this approach, reducing environmental impact and bringing economic, social, and environmental benefits.

The rest of this article is organized as follows: Section 2 presents some relevant research in the field of sustainable furniture design and QFD. Section 3 describes the research application of the integrated model AHP-QFD-AD. Section 4 describes the development of design applications based on the design solutions obtained from the integrated model. The design research methodology is discussed. Section 5 presents the conclusions of the study on sustainable furniture design.

2. Related Research

2.1. Sustainable Furniture Design

Sustainable development is becoming increasingly important in today’s society, and research in sustainable furniture design is receiving growing attention. Many experts and scholars have researched sustainable furniture design. For example, Deng Wenxin et al. [6] integrated sustainable design into furniture design and discussed the advantages of using bamboo materials in sustainable furniture, providing valuable references for the sustainable design research of bamboo furniture products. Wang Yaolin et al. [7] started his research on sustainable furniture design from the perspective of sustainable materials. He studied the recycling of waste materials and developed a new sustainable material by combining old textiles with starch, which is easy to process and has no adverse environmental impact. This research not only promotes waste recycling but also considers the degradation of furniture after damage, achieving the goal of sustainable design. Liu Jing et al. [8] developed a product-service system (PSS) framework in sustainable furniture design to provide theoretical references for researchers and decision-makers in sustainable development. Septiani M. et al. [9] integrated Design for Environment (DFE) models in the research process of sustainable furniture design to achieve eco-design. By employing relevant methods, more comprehensive decisions are made, enhancing the product’s environmental performance and providing a new theoretical basis for the development of sustainable furniture design. Sofiana Yunida et al. [10] innovated with thermoplastic recycled materials to offer new choices for sustainable development materials. This innovation in sustainable materials widens the selection path for innovative design in furniture and other design fields, reducing the environmental impact of product materials and aligning with sustainable development. Wronka A. et al. [11]. Discuss the links between circular economy concerns and wood-based panel technology, focusing on particleboard. It provides the method support for the recycling of particleboard materials. Kwangsawat, K. et al. [12] By investigating the local sustainable furniture consumption factors in Thailand, sustainable furniture design is carried out according to the market. Sustainable furniture will be closer to the needs of local users. Enhance the product power of sustainable furniture. M.M. Reham et al. [13] started the research on sustainable design with the analysis of interior residential design, dissecting the influencing factors of design. By applying sustainable materials, innovative solutions are provided for the application and design of residential furniture, designing interior furniture in line with sustainable development and enhancing overall functionality. Arianti Ayu Puspita et al. [14], considering the wide range of wood choices and good wood quality in Indonesia, explored sustainable design in the local wooden furniture industry to enhance the sustainable value of wooden furniture products, strengthen local industrial advantages, and ensure healthy development of local products and drives.

In conclusion, integrating recyclable materials into furniture design offers an effective strategy for waste recycling, simultaneously mitigating the environmental repercussions associated with material degradation following furniture disposal. However, there exists a gap in considering the sustainability of furniture across its entire usage lifecycle. The purpose of this paper is to address this gap by introducing the concept of whole life cycle design grounded in the use of sustainable materials. By incorporating this holistic approach, the aim is to enhance the overall sustainability of furniture products.

2.2. AHP Method

The Analytic Hierarchy Process (AHP) is widely recognized for calculating weights in design research. Chen M. et al. [15] enhanced AHP to integrate user needs into furniture design, showcasing its versatility. Liu M. et al. [16] combined AHP with fuzzy number sets for restaurant chair evaluation to enhance product popularity. Scholz S.W. et al. [17] used AHP to explore wooden dining table development, focusing on aligning furniture with consumer expectations. Liu L. et al. [18] applied AHP to gather user needs for furniture, using the GUCDR model to refine practical cases and enhance cultural depth. Chen M. et al. [19] utilized AHP and backpropagation neural networks to assess upholstered furniture, confirming its utility in simulating and making quality-based decisions.

In summary, the analytic hierarchy process offers a dependable means to calculate the weight of user needs, enabling designers to gauge their significance accurately. Even so, relying solely on this method might impede the practical integration of user needs. Consequently, this study employs a comprehensive evaluation approach to elevate product usability and more effectively cater to user requirements.

2.3. QFD Method

Many QFD (Quality Function Deployment) methods have been applied in design research in recent years. QFD is a systematic decision-making technique that translates customer needs into technical requirements through qualitative and quantitative analysis. Combining QFD with other ways to construct a scientific product evaluation system helps in the scientific and rational development of product design. Many experts and scholars have made attempts to apply this method. Wang Zongsheng et al. [20], in their research on the design of elderly walking aids, combined the QFD method with TRIZ (Theory of Inventive Problem Solving) theory to build an evaluation system for elderly walking aids design. By QFD, he created the correlation matrix between user needs and technical features, identifying technical contradictions and resolving them using TRIZ principles, ensuring the scientific design of elderly walking aids. Meichen Fang et al. [21] integrated the QFD method with the KANO model, Analytic Hierarchy Process (AHP), and PUGH decision matrix in their development of a medication app for older adults. This approach included classifying and selecting user needs, transforming them into prioritized functional requirements using QFD, and then using the PUGH decision matrix for active design proposal evaluation. The result was an optimized design and an improved user experience. Ref. [22] used the grey relational analysis method to prioritize and calculate relevant weights for emotional vocabulary in the sustainable design research of traditional wicker lamps. The QFD method was combined with fuzzy number sets to form a fuzzy QFD method, transforming emotional needs into design parameters and deriving optimal design parameters during the mapping process, enhancing the certainty of demand transformation and obtaining the best design parameters for product design. Angtuaco Danielle S. et al. [23] used the Green QFD method in the design research of toothpaste tubes, which was an innovative method of QFD for green quality deployment, and to study usability and sustainability issues. Used quantitative research to analyze user needs and develop sustainable products, improving performance. Wei Wei et al. [24], in the product innovation and development process, constructed a QFD innovative method called computer-aided quality function deployment for product optimization. CA-QFD is an innovative evaluation model that combines local joint analysis and quality function deployment, which more accurately reflects user needs in the product and provides a new method for future product development. Jing Liu et al. [25], in their research on the appearance design of a bundling machine, used the Analytic Network Process (ANP) and QFD to optimize and improve the appearance design. The product innovation method was optimized by innovatively reflecting the relationship between customer needs and engineering technical requirements, providing a new method for optimizing appearance design. Zhu Tian Lu et al. [26], in the development process of surgical auxiliary equipment, integrated the AHP-QFD-PUGH model to provide a new theoretical basis for product development. By analyzing user needs using AHP, he substituted the AHP weight into QFD to construct a relationship matrix with design features, transforming user needs into technical requirements. The PUGH decision matrix is then used to evaluate design proposals, providing innovative research ideas for developing surgical auxiliary equipment. Taifa et al. [27], in the development of classroom furniture, combined QFD and KANO models to grasp the furniture needs of students and carry out ergonomic design. This can reduce study fatigue and stress. Kuang Fengchun et al. [28], The QFD and TRIZ theory is integrated into small household furniture, transforming user needs into technical features, resolving contradictions, and cutting furniture dimensions. This innovation saves space. Lyu J et al. [29], Engineering analysis of customer requirements, weight, and product characteristics using QFD. Optimize open desks to enhance competitiveness. Erdil, A. [30] adopted the quality deployment method and the Pareto method for wooden furniture, which aligns more with the market demand. Xin Yi et al. [31], using QFD-TRIZ-FEM to transform housing quality problems, creative indicators are found. A high-quality children’s chair has emerged through knowledge, invention, and analysis.

In summary, the QFD method is essential for effectively translating user needs into technical features, thereby playing a central and skillful role in meeting user requirements through product design. QFD accurately reflects user requirements in product design. This study accomplishes this by applying an axiomatic design process, transforming user requirements into engineering requirements. Furthermore, it maps these requirements to feasible technical solutions, ensuring user needs are adequately considered. The independence principle in AD ensures the feasibility of the design scheme and provides a reliable method for optimizing and innovating the design.

2.4. Axiomatic Design Method

Axiomatic design is a scientific guideline in the field of design that aims to guide designers to make accurate decisions in the design process [32] and provide an effective way of thinking for innovative design or improvement of existing design. In the field of design research, many scholars have taken axiomatic design into consideration. The combination of axiomatic design and TRIZ theory [33] can produce more desirable design solutions in the product development process. The integration of hierarchical analysis and axiomatic design [34], on the other hand, helps to ensure that design solutions are more in line with user needs. Furthermore, the combination of axiomatic design with the modular design approach of the design structure matrix [35] can efficiently arrange the application of product modules in the design sequence. In computer-aided design research [36], a fuzzy design solution evaluation model can be constructed and applied to adjust the design parameters of coupled problems in design to obtain appropriate solutions more easily. This approach can help designers to generate innovative solutions and make accurate decisions.

In summary, axiomatic design is crucial in design methodology and technical optimization due to its strong connection with the feasibility of design schemes and alignment with user needs. Accurately translating user requirements into technical solutions is a crucial problem worth exploring.

3. Research Method

The importance of sustainable design in furniture design is growing significantly. To ensure that products not only adhere to the principles of sustainable development but also cater to customer needs, an effective furniture design evaluation system is established, incorporating mathematical models.

This study centers around the design of a storage rack as a foundation for sustainable design. To facilitate this process, an integrated AHP-QFD-AD evaluation model is developed (Figure 3). The starting point involves identifying user requirements through thorough user research and determining their relative significance via the AHP method. Subsequently, an analysis of functional necessities for product design is conducted, incorporating the QFD approach. This involves merging the identified user needs with pertinent requirements within the House of Quality (HoQ) and assigning appropriate weight values to these requirements. The next step integrates the AD principle by selecting multiple relevant requirements and translating them into tangible design parameters. The viability of the design scheme is demonstrated by adhering to the independence axiom, thereby confirming that the product design is in harmony with user needs while seamlessly incorporating the ethos of sustainable design of storage racks. Ultimately, the output design scheme undergoes assessment using the Likert scale, gauging the efficacy of the product design. This comprehensive methodology permits the creation of a sustainable and user-centric design for the storage rack, serving as a benchmark for forthcoming furniture design ventures.

3.1. User and Market Research

Sustainable design implementation within the furniture design domain frequently centers on the adoption of sustainable materials. Conventional furniture manufacturing methods involving paints and adhesives can adversely affect the environment and run counter to the principles of sustainable development.

Various sustainable furniture materials are being explored and integrated into the contemporary furniture market. These categories include standard hardwood furniture, wood-based panel furniture, metal furniture, organic furniture, new bio-based furniture, and recyclable furniture. The advantages and disadvantages of these materials are apparent (

Table 1. Materials for sustainable furniture.

Material Type	Species	Advantage	Shortcoming
1. Hardwood	From sustainable forests, durable, long life.	Natural beauty, high texture appearance.	Deforestation impacts limited supply.
2. Artificial panels	Made of recycled wood fiber, environmentally friendly.	Cost-effective, less waste.	Some adhesives may contain harmful chemicals.
3. Metal materials	Recyclable, long life.	Solid, modern design style.	Energy-intensive production processes.
4. Organic materials	Made of renewable materials and biodegradable.	Environmentally friendly, natural and uniquely designed.	Material selection is limited and may not be very durable.
5. Bio-based materials	Made of biodegradable materials, environmentally friendly.	Sustainable, reducing reliance on plastics.	Emerging technology, limited market supply.
6 Recyclable materials	Designed for easy disassembly and recycling.	Reduce waste and promote a circular economy.	Design options are limited, and durability issues may arise.

). A close examination of the types and properties of these used materials reveals that using a single sustainable material in furniture design can bring limited benefits.

We conduct market research on consumer preferences to obtain user demand for sustainable furniture products and obtain customer needs through questionnaires and interviews in the furniture market. Then, we organize user evaluation of sustainable furniture in online shopping malls, select more user needs to obtain the functional characteristics of existing mature products and analyze the user needs solved by the functions. The 16 most mentioned user needs were selected and grouped into four main areas (

Table 2. User demand table.

Layer	Requirement
Appearance	Soft material
	Proportional coordination
	Plain color
	Simple style
Structure	Harmless design
	Sustainability
	Strong security
	Good stability
Functions	Various forms of storage
	Suitable for multiple environments
	Ample storage space
	Good decorative effect
Interaction	Free combination
	Replaceable unit
	Easy to operate
	Easy maintenance

).

3.2. AHP User Demand Analysis

The Analytic Hierarchy Process (AHP), pioneered by Professor Saaty [37], is utilized to prioritize the aforementioned user requirements. In this endeavor, 16 pertinent needs are identified, and the AHP methodology is applied to perform a weight analysis of the factors influencing these demands.

The user needs obtained from market research are numbered, the hierarchical analysis model of multifunctional shelf design is established, and the analytic hierarchy process is applied to calculate the weight of the shelf. This model comprises three levels: the target layer, criterion layer, and indicator layer (Figure 4). In this context, the multifunctional shelf design constitutes the target layer, while user needs are segmented into criteria layers—namely, Appearance (S1), Product Performance (S2), Functions (S3), and interaction (S4). The set of 16 user requirements is positioned within the indicator layer. By establishing a well-defined hierarchy of weights within the AHP model, the relative significance of each user requirement is ascertained. This methodology facilitates more informed decision-making throughout the sustainable storage rack design process.

In the weight calculation of AHP, it is necessary to build a reasonable judgment matrix and compare the importance of each element at the same level. Set each vector element of the judgment matrix to $s_{ij}$, $s_{ij}>0$. $s_{ij}\times s_{ji}=1$. Then, it is judged that the matrix value is reasonable.

According to the evaluation results of each level of evaluation indicators, the complementary judgment matrix is constructed by $D={(s_{ij})}_{n\times n}$:

$$D={(s_{ij})}_{n\times n}=\left[\begin{array}{l}{S}_{11} S_{12} \cdots S_{1n}\\ S_{21} S_{22} \cdots S_{2n}\\ \cdots \cdots ⋮ \cdots \\ S_{n1} S_{n2} \cdots S_{nn}\end{array}\right] (S_{ij}>0, S_{ij}\times S_{ji}=1)$$

(1)

To create the judgment matrix, we collected evaluations from various experts and participants using a 1–9 scale (

Table 3. Scale Table 1–9.

Scale	Expression
1	Of equal importance
3	Slightly more important
5	Obviously always
7	Strongly important
9	Extremely important
2, 4, 6, 8	Median value of two adjacent values determined
Count backwards	Inverse value

). From a sustainability perspective, factors affecting the target layer, i.e., appearance, structure, function, and interaction, were assessed by professors, design major students, furniture designers, consumers, and sellers in the field of furniture design.

According to the judgment matrix, the arithmetic average method is used to calculate the weight. The calculation formula of the weight vector is as follows:

$$\omega i=\frac{1}{n}{\displaystyle \sum _{j=1}^n\frac{s_{ij}}{{\displaystyle \sum _{k=1}^n{s}_{kj}}}} (i,j=1,2,\cdots ,n)$$

(2)

According to Equation (2), the judgment matrix of the target layer is constructed in

Table 4. Target layer judgment matrix table.

Target Layer	S1	S2	S3	S4	ω
S1	1	1/4	1/6	1/4	0.06
S2	4	1	1/3	1/2	0.18
S3	6	3	1	3	0.51
S4	4	2	1/3	1	0.25

:

According to Equation (2), the hierarchy judgment matrix of modeling is listed in

Table 5. Judgment matrix for Shape (S₁).

S1	S11	S12	S13	S14	ω1
S11	1	1/3	2	1	0.21
S12	3	1	3	1	0.40
S13	1/2	1/3	1	1/2	0.12
S14	1	1	2	1	0.27

:

According to Equation (2), the product performance hierarchy judgment matrix is constructed in

Table 6. Judgment matrix for Product performance (S₂).

S2	S21	S22	S23	S24	ω2
S21	1	1/2	1/4	1/3	0.10
S22	2	1	1/2	3	0.29
S23	4	2	1	2	0.42
S24	3	1/3	1/2	1	0.19

:

According to Equation (2), the functional hierarchy judgment matrix is constructed in

Table 7. Judgment matrix for Function (S₃).

S3	S31	S32	S33	S34	ω3
S31	1	1/2	3	2	0.18
S32	2	1	2	1	0.29
S33	1/3	1/2	1	1	0.44
S34	1/2	1	2	1	0.09

:

According to Equation (2), the interaction hierarchy judgment matrix is constructed in

Table 8. Judgment matrix for interaction (S₄).

S4	S41	S42	S43	S44	ω4
S41	1	1	3	4	0.40
S42	1	1	2	3	0.34
S43	1/3	1/2	1	2	0.16
S44	1/4	1/3	1/2	1	0.10

:

After calculating the weight of each matrix and obtaining the weight vector, it is essential to conduct a consistency test on the judgment matrix to ensure the accuracy and reliability of the Analytic Hierarchy Process (AHP) results and avoid errors caused by subjective judgments. The consistency test is done using the Consistency Ratio (CR), which measures how consistent the judgment matrix is. The first step to calculating the CR value is determining the judgment matrix’s maximum eigenvalue λ_max, which is obtained based on the weights of each judgment matrix.

The formula for calculating the maximum eigenroot is:

$${\lambda }_{\max }=\frac{1}{n}{\displaystyle \sum _{i=1}^n\frac{\left({\mathrm{AW}}_i\right)}{{\mathrm{W}}_i}}$$

(3)

After obtaining the maximum feature root, the consistency index CI value is calculated by substituting it into the formula, where n is the order of the matrix:

$$\mathrm{CI}=\frac{{\lambda }_{\max }-n}{n-1}$$

(4)

The Consistency Index (CI) values for both the target layer and each criterion layer are computed and then compared with Random Index (RI) values. The consistency check formula is applied in this context. If the resulting CR is below 0.1, it signifies that the judgment matrix established by AHP exhibits a relatively consistent structure. This outcome is indicative of the reliability of our evaluation procedure, thus enhancing the precision and efficacy of decision-making and further reinforcing our credibility.

The CI and RI values are substituted into the formula to check consistency.

$$\mathrm{CR}=\frac{\mathrm{CI}}{\mathrm{RI}}$$

(5)

Consistency test results at all levels were obtained in

Table 9. Consistency check table at all levels.

Layer	λmax	CI	RI	CR	Result
Criterion layer	4.122	0.041	0.890	0.046 < 0.1	Pass
S1	4.118	0.039	0.890	0.044 < 0.1	Pass
S2	4.237	0.079	0.890	0.089 < 0.1	Pass
S3	4.249	0.083	0.890	0.093 < 0.1	Pass
S4	4.031	0.010	0.890	0.012 < 0.1	Pass

:

According to Table (Table 9), the CR value of the target layer matrix is 0.046, and it is smaller than 0.1. The CR values of matrixes in the criterion layer are 0.044, 0.089, 0.093, and 0.012, and all of them are smaller than 0.1, so the matrices in each layer pass the consistency test.

To determine the ranking of user requirements and their final weight values, each weight value from the criterion layers is multiplied by the weight value of the target layer (

Table 10. Final weights.

Target Layer	Target Layer Weight	Criterion Layer	Weight of Each Criterion Layer	Final Weight	Priority Ranking
Appearance (S1)	0.06	Soft material	0.21	0.0126	15
		Proportional coordination	0.40	0.0240	12
		Plain color	0.12	0.0072	16
		Simple style	0.27	0.0162	14
Product Performance (S2)	0.18	Environmentally friendly materials	0.10	0.0180	13
		Sustainability	0.29	0.0522	7
		Strong security	0.42	0.0756	6
		Good stability	0.19	0.0342	10
Functions (S3)	0.51	There are various forms of storage	0.18	0.0918	3
		Suitable for multiple environments	0.29	0.1479	2
		Ample storage space	0.44	0.2244	1
		Good decorative effect	0.09	0.0459	8
Interaction (S4)	0.25	Free combination	0.40	0.1000	4
		Replaceable unit	0.34	0.0850	5
		Easy to operate	0.16	0.0400	9
		Easy maintenance	0.10	0.0250	11

). Notably, the functional requirement level holds the most substantial portion within the target weight. Meanwhile, the index within the criterion level boasts the highest proportion. This prominence is attributed to the ample storage space available within the functional group, followed by its versatility in accommodating various environments. Additionally, the diversity in storage forms also contributes to this outcome.

3.3. QFD Transforms Functional Requirements

This method converts user requirements into product design quality attributes—a process termed system expansion [38]. This systematic approach extends user needs to each product attribute, progressing to the quality of individual components and production processes. Ultimately, this comprehensive process determines the overall product quality. Such systematic expansion ensures that the product aligns with user needs and maintains effective quality control during development.

AHP determines the weight of user demands, with each user’s needs ($S_i$) forming the foundation for a solution addressing functional requirements ($P_i$). These needs are then translated into product technical characteristics through the House of Quality framework. This process enhances the design team’s understanding of user needs, facilitating targeted decisions in product design and ultimately ensuring alignment with user expectations.

Based on the outcomes of AHP, the weights for user needs are determined, and a thorough analysis of the functional requirements needed to satisfy these user needs is conducted. Taking into account the inherent characteristics and structure of the sustainable storage rack itself, it can be categorized into four types of functional requirements (

Table 11. Function classification requirements table.

Primary Functional Requirement	Secondary Functional Requirement
P1 Studdle	P11 Base reinforcement
	P12 Height adjustable
P2 Laminate	P21 Mesa combination change
	P22 Easy assembly and disassembly
P3 Structure	P31 Ergonomic design
	P32 Modularization
	P33 Full life cycle design
	P34 Avoid sharp edges
P4 Appearance	P41 Simple and atmospheric
	P42 Modeling stability and environmental protection

): studdle (P1), laminate (P2), structure (P3), and appearance (P4). These classifications and specifications enhance the clarity of the multifunctional shelf’s design requirements, enabling a more structured and effective approach to its development.

It is calculated according to the relationship matrix of user demand importance and functional demand. Suppose the significance of the requirement of the ith user is $C_i$. Then, the value corresponding to the strength of the relationship between the ith user requirement and the jth functional requirement is $R_{ij}$. $W_j$ is the importance of the j_th applicable requirement.

QFD technical feature importance calculation formula:

$$W_j={\displaystyle \sum _{i=1}^n{C}_i{R}_{ij}}$$

(6)

The relative importance of QFD technical features is calculated as follows:

$${W_j}^{*}=\frac{W_j}{{\displaystyle \sum _{i=1}^m{W}_j}}$$

(7)

The essence of the QFD approach centers on constructing HoQ, which visually portrays the interrelationships and weights among product design elements. The main framework of the HoQ includes a relationship matrix created by merging user needs’ weights from AHP with the functional requirements of the product design. This integration categorizes relationships between user needs and functional requirements into four correlation levels: strong, medium, low, and no correlation. These levels gauge the connection between different aspects. Each cell in the relationship matrix is assigned a value based on correlation level. Systematically analyzing and quantifying the interplay between user needs and functional requirements, HoQ emerges as a powerful tool guiding the product design journey.

Bring these user and functional requirements into HoQ (Figure 5).

The essence of the QFD approach centers on constructing HoQ, a graphical representation that visually portrays relationships and weights among product design elements. The main framework of the House of Quality encompasses a relationship matrix formed by incorporating user needs’ weights derived from the AHP analysis. This matrix is pivotal for comprehending the interplay between user needs and functional requirements. Within HoQ, a structured matrix captures relationships between user needs and functional requirements. This process outlines five distinct functional requirements: modularization, table combination change, whole life cycle design, convenient assembly and disassembly, and height adjustment. This yields a comprehensive and well-defined set of functional requirements (Figure 6).

By adopting the QFD method, the modular design requirements are smoothly integrated into the shelf design. This not only extends the service life of the shelf but also provides a critical support basis for the technical realization of sustainable furniture design below. The five applicable requirements with relatively high weight are transformed into design parameters through AD axiom design and implemented into product design to ensure that product-applicable conditions are accurately transformed into design and fit user requirements.

3.4. AD Design Independence Axiom Proof

Axiomatic Design is a method first proposed by Professor Suh N.P. [39] in 1990. The function is to transform user requirements into technical means in the design field and obtain the optimal solution of the design scheme through axiomatic principles.

In the QFD method, five critical functional requirements {FR} are correlated with corresponding design parameters {DP} (

Table 12. Mapping between functional requirements and design parameters.

No.	Functional Requirements (FR)	No.	Design Parameters (DP)
FR1	Modular design	DP1	Flexible component combination design
FR2	Mesa combined transform	DP2	Suspension rod and laminate combination design
FR3	Full life cycle design	DP3	Product use process design
FR4	Easy assembly and disassembly	DP4	Joint fixation design
FR5	Adjustable height	DP5	Telescopic support rod design

), forming the physical domain. This mapping ensures a harmonious relationship between each functional requirement and specific design parameters, clarifying their interconnection during the design phase. The following step involves testing the design matrix using the independence axiom. This principle guarantees that functional requirements and design parameters remain autonomous, avoiding unnecessary coupling. Upholding this axiom ensures effective fulfillment of each applicable requirement and enables multiple functional requirements to be met by individual design parameters. Leveraging insights from the axiomatic design (AD) theory, the multifunctional shelf’s functional requirements {FR} are meticulously linked with the design parameters {DP} in the physical context. This alignment guarantees the precise satisfaction of each functional requirement while allowing each design parameter to address multiple requirements proficiently. By adhering to QFD method principles and the AD design theory, the multifunctional shelf’s design optimally caters to user needs. This approach fosters a highly effective, well-balanced product design, resulting in a multifunctional shelf that genuinely fulfills customer expectations.

There is a mapping relationship between the functional requirements and design parameters of the storage rack, and the formula can be expressed as:

$${\left\{FR\right\}}_{m\times 1}={\left[T\right]}_{m\times n}{\left\{DP\right\}}_{n\times 1}$$

(8)

${\left\{FR\right\}}_{m\times 1}$ is the functional demand vector, ${\left\{DP\right\}}_{n\times 1}$ is the design parameter vector, ${\left[T\right]}_{m\times n}$ is the product design matrix, and the above formula is the product design relationship equation. It can be expressed as:

$$\left[T\right]=\left[\begin{array}{l}{T}_{11} T_{12} \cdots T_{1m}\\ T_{21} T_{22} \cdots T_{2m}\\ ⋮ ⋮ \cdots ⋮\\ T_{n1} T_{n2} \cdots T_{n\mathrm{m}}\end{array}\right]$$

(9)

The elements of the matrix [T] are determined by the following formula:

$$T_{ij}=\frac{{\partial FR}_i}{{\partial DP}_j}$$

(10)

The ${\left\{FR\right\}}_{m\times 1}$ of each element of a functional requirement can be expressed as:

$${FR}_i={\displaystyle \sum _{j=1}^n{A}_{ij}D{P}_j} (i=1,2,\cdots ,m)$$

(11)

The design matrix [T] classifies design into three cases: uncoupled, quasi-coupled, and coupled. When [T] is diagonal (A-shape), functional requirements and design parameters are independent. This uncoupled design allows separate parameters to meet each requirement independently, ensuring simplicity and reliability. For a triangular [T] (B-shape), a specific parameter order exists. They should be arranged properly to meet axioms while retaining some correlation, forming a quasi-coupled design. This maintains controllability and partial independence. A general [T] (C-shape) implies strong coupling or dependency. Changes in parameters affect each other, lacking independent compliance assurance. This coupled design does not meet axioms, jeopardizing meeting requirements and introducing uncertainties.

$$\left[T\right]=\underset{\mathrm{A}\text{-}\mathrm{shape}}{\left[\begin{array}{l}{T}_{11} 0 0\\ 0 T_{22} 0\\ 0 0 T_{33}\end{array}\right]} \left[T\right]=\underset{\mathrm{B}\text{-}\mathrm{shape}}{\left[\begin{array}{l}{T}_{11} 0 0\\ T_{21} T_{22} \hspace{0.17em}0\\ T_{31} T_{32} T_{33}\end{array}\right]} \left[T\right]=\underset{\mathrm{C}\text{-}\mathrm{shape}}{\left[\begin{array}{l}{T}_{11} 0 T_{13}\\ T_{21} T_{22} 0\\ T_{31} T_{32} T_{33}\end{array}\right]}$$

According to the above principles and formulas, the relationship matrix between the functional requirements of the independence axiom and design parameters is constructed. By considering the design of mechanical systems from an axiomatic point of view, we can use binary coding to represent the relationship between functional requirements and design parameters. In this representation, 1 is strongly correlated, indicating that there is a clear association between {FR} and {DP}, and 0 is irrelevant, indicating that there is no association between {FR} and {DP}. According to the mapping table relationship, the matrix is:

$$\left[\begin{array}{l}F{R}_1\\ F{R}_2\\ F{R}_3\\ F{R}_4\\ F{R}_5\end{array}\right]=\left[\begin{array}{l}1 0 0 0 0\\ 0 1 0 0 0\\ 0 0 1 0 0\\ 0 0 0 1 0\\ 0 0 0 0 1\end{array}\right]\left[\begin{array}{l}D{P}_1\\ D{P}_2\\ D{P}_3\\ D{P}_4\\ D{P}_5\end{array}\right]$$

The diagonal design matrix [T] signifies independence between functional requirements and design parameters, devoid of coupling or interdependence. This uncoupled design aligns with the axiomatic method’s independence hypothesis. The theory of freedom confirms that each functional requirement can be met using separate design parameters that do not interact.

Axiomatic analysis reveals that mapped design parameters are logically reliable, offering essential support for design efforts. Integrating axiomatic design enhances technology realization and improves the conversion of functional requirements.

The shelf’s modular design is achieved via a theoretical model, ensuring optimal material and resource utilization. This simplifies maintenance, extends product lifespan, and minimizes disposal and replacement. Additionally, it enhances product adaptability to various environments. In short, this approach improves lifecycle management. This straightforward, reliable process results in a multifunctional shelf perfectly aligned with user needs, boasting impressive functionality and performance.

4. Case Study

The design parameters are derived through AD axiom design, aiding the creation of a sustainable storage rack design. Additionally, the concept of whole life cycle design, a tenet of sustainable design, is integrated into the design of a storage rack to enhance its sustainability attributes. Through the incorporation of the AHP-QFD-AD model, user requirements are effectively translated into functional requirements, and these applicable requirements are subsequently mapped to specific design parameters. This seamless integration streamlines the conversion process of user needs and amplifies the overall product performance of the multifunctional storage shelf.

4.1. Sustainable Modeling Design

Materials for the storage rack design prioritize recyclable and biodegradable options for enhanced sustainability [40]. The main selection is biodegradable bamboo, supplemented by selected hardwood materials and biodegradable plastics. According to the parameters in the icon, product stability can be effectively enhanced (

Table 13. Sustainable furniture material physical parameters reference table.

Materials	Physical Parameter
Wood	Density: 500–800 kg/m3
	Elastic modulus: 10–20 GPa
	Tensile strength: 40–150 MPa
	Compressive strength: 30–80 MPa
Bamboo	Density: 400–800 kg/m3
	Elastic modulus: 8–18 GPa
	Tensile strength: 70–150 MPa
	Compressive strength: 30–60 MPa
Recycled plastics	Density: 800–1300 kg/m3
	Elastic modulus: 1–4 GPa
	Tensile strength: 20–100 MPa

). The lamination process involves bamboo fiber heating and accessible bending technology, ensuring durability and an eco-friendly structure. Supporting rods are reinforced with hardwood, while non-slip caps at the bottom use degradable plastic, increasing friction and stability. The design of the storage rack adheres to ergonomic principles, prioritizing user convenience. Dimensions are carefully set at a 40 cm height for each layer, totaling 80 cm for two layers. The shelf measures 30 cm in depth and 60 cm in width, effectively meeting daily usage needs with a balanced and functional design.

The AD axiom design establishes a link between the functional and physical domains using five specific design parameters: DP1: Component flexible combination design, DP2: Suspension rod and lamellar combination design, DP3: Product use process design, DP4: Connection fixed joint design, DP5: Support rod expansion design (

Table 14. Storage rack design.

Shelf Layer Plate Fixed Shaft Design	Shelf Laminate Combination Design	Shelf Joint Design	Shelf Support Rod Design

).

The design of a sustainable storage rack revolves around these parameters, ensuring both eco-friendly construction and efficient functionality. By integrating recyclable and biodegradable materials and implementing thoughtful product design, the outcome is a practical, user-friendly, and environmentally conscious storage rack. This culmination embodies the incorporation of sustainable design principles, resulting in a product that caters to user needs while also fostering environmental responsibility.

Using the specified technical parameters, a highly detailed design for a storage rack has been carefully crafted. The shelf consists of six essential components: fixed shaft, suspension rod, middle plate, edge plate, support rod, and non-slip cap (

Table 15. Parts design of storage rack.

Part name	Blueprint
fixed shaft
suspension rod
Intermediate plate
marginal plate
support rod
non-slip cap

). By skillfully integrating the edge plate, suspension rod, and fixed shaft, the shelf’s configuration can be effortlessly adjusted. This empowers users to tailor the shelf according to their unique needs and preferences. The storage shelf is securely anchored using screw buttons, supplemented by the stability-enhancing non-slip cap at the base. This dual mechanism guarantees comprehensive safety and stability, effectively minimizing any potential risks of accidents or instability. Additionally, the support rod incorporates an expansion function, creating extra hanging space for the shelf. This notable improvement significantly amplifies the shelf’s adaptability, making it suitable for a variety of situations and capable of accommodating diverse storage requirements.

The storage rack is designed with practicality and user convenience in mind (Figure 7). Its adjustable form and stable construction make it an excellent solution for organizing and maximizing storage space. Incorporating safety features such as the knob fixing mode and anti-slip caps ensures the shelf is safe to use in various environments. The expandable support rods improve its adaptability and make it suitable for multiple storage applications.

4.2. Sustainable Product Life Cycle Design

Following the sustainable design principle of the whole life cycle, storage shelves are divided into six stages: material mining, manufacturing, use, maintenance, waste treatment and material recovery [41]. The modular design of the shelving allows easy adaptation to changing needs and environments. If parts break, they can be removed and reassembled, reducing waste. Bamboo is the primary material, recyclable into bamboo charcoal post-disposal. This charcoal can then be repurposed, improving recycling efficiency.

The sustainable evolution of the storage rack involves periodic design adjustments that extend its operational lifespan. Starting as a triple shelf (Figure 8), it can transform into a retractable shelf (Figure 9) and further develop into a desk shelf (Figure 10). This evolving process empowers the storage rack to adapt to changing requirements and dynamic environments, ultimately enhancing its overall durability. Even in cases of component damage, the shelf can remain functional by reconfiguring and reducing the affected components, eliminating the need for a complete shelf replacement. When a sustainability shelf is no longer used, its bamboo materials can be easily broken down, minimizing environmental impact. The shelf can also be burned to create bamboo charcoal for making tableware, soap, and other products.

A life cycle assessment is performed by comparing the environmental impact of the life cycle of a sustainable shelf with that of a hardwood shelf (

Table 16. Comparison of the environmental impact of the whole life cycle of sustainable shelving.

Stages	Sustainable Shelving	Hardwood Shelving
1. Material mining	The maturity cycle of raw materials is 3–5 years	The maturity cycle of raw materials is 60–100 years
2. Manufacturing phase	The manufacturing process is simple	The manufacturing process is more complex
3. Use phase	Damaged disassembly can be used normally	High scrap rate due to damage
4. Maintenance phase	Low maintenance cost	High maintenance cost
5. Scrap disposal	Lower incineration carbon emission	Higher incineration carbon emission
6. Material recycling	Bamboo charcoal can be made into economic products	The recycling rate of ash residue is low

). Bamboo materials absorb more carbon dioxide as they grow up. The growth cycle of bamboo materials is much shorter than that of wood and will not impact the ecosystem. At the manufacturing phase, sustainable shelving has fewer production steps than hardwood shelving due to its modular design. Sustainable shelving can be used by removing damaged parts to keep them in daily use. A sustainable, shelf-free combination design makes it easier to maintain. At the waste treatment stage, bamboo furniture is more easily degraded than traditional furniture materials (Figure 11), and less carbon dioxide is generated by incineration. Sustainable shelves made from bamboo can be burned to produce bamboo charcoal, which can be widely used as a raw material for everyday products. Compared with the recovery of hardwood after incineration, bamboo charcoal has a higher reuse value.

In summary, sustainable frame designs offer longer shelf life, reducing environmental impact and increasing recycling value compared to traditional hardwood shelves. This design approach significantly contributes to the favorable development of sustainable furniture.

4.3. Evaluation of Design Scheme

Based on the finalized design scheme, a comprehensive evaluation and summary are conducted to validate the implementation of the design. A questionnaire is used to gather insights from market consumers, and the obtained data is subjected to analysis. The design scheme’s effectiveness is measured using four key indicators: shape, product performance, function, and interaction. To gauge consumer responses, a Likert scale (Table 16) is constructed, utilizing a 1–5 rating system. We select 80 customers in the furniture market, evenly distributed in four age groups—teenagers, young adults, middle-aged, and elderly. In each age group, there are ten males and ten females. Their questionnaire responses underwent thorough collection and comprehensive analysis. The most frequently selected values determined final metric scores within each age bracket. These scores are meticulously presented in designated data tables (

Table 17. Likert statistical scale.

No.	Appearance	Structure	Functions	Interaction
Adolescent males	4	5	3	5
Adolescent females	4	4	5	4
Young males	3	4	4	5
Young females	5	5	5	4
Middle-aged males	5	3	4	3
Middle-aged females	3	5	3	5
Elderly males	5	3	5	4
Elderly females	5	3	5	5

). Significantly, most scores cluster within the “3, 4, 5” range, with no instances of lower scores “1 or 2.” This pattern provides compelling evidence of our program’s smooth implementation and remarkable alignment with market demands.

4.4. Discussions

This paper introduces a novel approach to sustainable furniture product development, aiming to overcome challenges often encountered in conventional sustainable design practices. While the typical focus of sustainable furniture design is integrating eco-friendly materials, this approach extends its scope to consider the entire product usage lifecycle. Additionally, using newly introduced recyclable waste materials requires ongoing research to ensure stability and hardness. Insufficient strength and hardness can render furniture susceptible to damage in various environments. Developing sustainable furniture requires a delicate balance between addressing user needs and upholding sustainable design principles. To address this challenge, the study integrates the AHP-QFD-AD model, offering a unique methodology for product development.

Previous studies combined the QFD method with techniques of AHP and KANO models to prioritize user demands. This aids in establishing weighted rankings for user needs, which are then integrated into HoQ to form the relationship matrix between user needs and design requirements. Practical design solutions are formulated by determining the weight ranking of design requirements, culminating in product development aligned with user expectations.

Previous studies obtained user requirements by AHP and then translated them into functional requirements by substituting QFD. On this basis, this study integrates the AD design method. AD axiomatic design maps these functional requirements into design parameters and proposes tailored technical solutions to meet user expectations precisely. The verification of the independence axiom ensures the feasibility of the design scheme, provides reliable support for the successful implementation of the design, and enables the smooth realization of the final product.

Integrating the AHP-QFD-AD model empowers designers to make well-informed design decisions, strengthening the efficacy of sustainable furniture products and enhancing user satisfaction. This innovative approach extends the product lifecycle of sustainable furniture, embodying the principles of sustainable development. By addressing the potential adverse environmental impacts of furniture usage, this methodology contributes to a greener and more sustainable future.

However, it must be admitted that this method also has certain limitations. The research method of user demand needs to be improved, and the application of the analytic hierarchy process has a particular subjectivity. This research focuses on developing and studying new sustainable furniture products and has yet to form a mature framework for sustainable furniture recycling. The assessment of the life cycle of furniture needs to be strengthened. The role of computer-aided in the research of sustainable design is becoming more and more significant. The application of the BP neural network, convolutional neural network model, and other technical means in the research of sustainable furniture design remains to be explored. The study will continue as to the following research question.

5. Conclusions

This study integrates sustainable development concepts in furniture design, comprehensively analyzing research methodologies and sustainable design’s current status. It navigates the product development process of sustainable furniture and concludes with the following findings:

• Enhanced Durability and Material Firmness: Sustainable design bolsters furniture product durability and material firmness. Leveraging diverse, sustainable materials while considering their characteristics increases stability and firmness. This resilience enables products to adapt to environments, extending their service life.
• Reduced Environmental Impact via Whole Life Cycle Integration: Integrating the whole life cycle concept mitigates furniture products’ environmental impact. The sustainable design prioritizes material sustainability and uses product life cycle theory to address loss, usage time, and environmental factors. Modular design removes damaged components, reducing waste, promoting eco-friendliness, and extending product lifespan.
• Integrated AHP-QFD-AD Model for Targeted Development: Applying the AHP-QFD-AD model transforms user needs into functional demands and maps them onto design parameters. This systematic approach uses targeted technologies and axiom verification to align with user needs effectively.
• Scientific Design Evaluation and Consumer Assessment: Including the independence axiom in design evaluation and consumer feedback substantiates the design scheme’s feasibility. This approach expedites innovative, sustainable product development.

While this study proficiently explores sustainable furniture development and integrates the product life cycle theory, some areas need refinement. Research on damaged component recyclability needs attention. User research should aim for specificity and objectivity to guide precise development decisions. The sustainable furniture development system requires ongoing refinement for a streamlined framework. This research underscores sustainable development’s growing importance amid environmental challenges, aligning with societal trends and environmental preservation. It plays a pivotal role in harmonizing humanity and nature. Ultimately, this study serves as a foundational resource, paving the way for enhancing the sustainable furniture development framework.