Description:FIELD OF INVENTION
The present invention relates to the field of nonwoven composite materials, particularly to sustainable, high-performance acoustic and thermal insulating nonwovens. More specifically, the invention pertains to hybrid nonwoven composites comprising natural fibers obtained from agricultural waste, such as banana fibers, in combination with recycled thermoplastic fibers, including recycled polyester (PET) and optionally blended with low-melt PET fibers and other natural fibers like wool.
The invention further relates to optimized manufacturing processes, including fiber selection, blending, web formation via dry-laid carding, and bonding techniques such as thermal bonding and needle punching, aimed at achieving high noise reduction coefficient (NRC), thermal insulation (R-value), dimensional stability, and structural integrity, while maintaining recyclability, biodegradability, and industrial scalability.
BACKGROUND OF THE INVENTION
The background for the invention arises from the increasingly recognized environmental, industrial, and residential challenges associated with noise pollution and inefficient thermal insulation. Urban environments, industrial facilities, transportation systems, and residential buildings face high noise exposure levels, which can cause physiological and psychological harm, including hearing impairment, stress, and sleep disturbances. Existing materials for acoustic and thermal insulation, such as mineral wool, glass wool, polyurethane foams, and synthetic fiber mats, are associated with environmental drawbacks, health hazards, or trade-offs in performance. Mineral and glass wool, while effective in absorption, produce fibro genic dust and require careful handling, storage, and disposal. Polyurethane and polyester foams, though mechanically robust, rely on non-renewable petrochemical resources and are generally non-biodegradable and difficult to recycle, limiting their ecological acceptability. Natural fiber mats derived from coir, jute, or kenaf, while renewable, often suffer from poor dimensional stability, low tensile strength, and variable acoustic efficiency, rendering them unsuitable for demanding industrial and architectural applications.
Nonwoven fibrous materials are extensively employed for acoustic insulation in applications spanning the automotive, construction, HVAC, and appliance sectors. Conventional nonwoven acoustic materials predominantly utilize synthetic fibres such as polyethylene terephthalate (PET), polypropylene (PP), or glass wool. These materials, while effective in sound attenuation, suffer from inherent disadvantages including non-biodegradability, adverse environmental impact, flammability, and health hazards due to fibre dust and chemical additives.
Banana fibre, an underutilised lignocellulosic fibre extracted from agro-waste, exhibits inherent flame retardancy due to its phosphorus content, high porosity, and favourable sound absorption characteristics. However, the standalone use of banana fibre poses challenges such as poor structural integrity, limited durability, and compatibility issues with conventional bonding processes. There exists a technological void in leveraging banana fibre synergistically with thermoplastic binders to create high-performance acoustic insulation materials that are sustainable and compliant with modern environmental regulations.
Several studies and patents have explored the use of natural fibers and polymers in insulation materials:
WO2016110647A1 discloses a fibrous thermal insulating material comprising a homogeneous mixture of fibers derived from banana plant flowering stalks and a binder consisting of synthetic polyester fibers. The invention focuses on providing thermal insulation in building and industrial applications, emphasizing lightweight and eco-friendly characteristics derived from natural fibers. The patent describes processing steps including cleaning, drying, cutting, and mixing of banana fibers with polyester fibers, followed by formation into a fibrous mat through conventional web formation and bonding techniques. The resulting material demonstrates effective heat retention and reduced thermal conductivity, suitable for insulation panels, wall linings, and ceiling applications. However, the material primarily addresses thermal insulation and does not specifically disclose acoustic absorption or synergistic performance when combined with synthetic fibers for sound damping. Furthermore, mechanical strength and dimensional stability under varying environmental conditions are not emphasized. While this reference highlights the potential of banana fibers in insulation, it does not anticipate or suggest the hybridization with rPET fibers to simultaneously achieve high acoustic and thermal performance, which is the subject of the present invention.
AU2011251882B2 relates to a material used as thermal and/or sound insulation, comprising microfibers obtained from the stem fibers of banana fruit trees. The invention focuses on leveraging the natural cellular and porous structure of banana fibers to achieve both heat resistance and sound absorption, particularly in residential and industrial applications. The disclosed fibers are processed into mats or panels through mechanical alignment and bonding, producing a material that exhibits improved resistance to heat and cold fluctuations, along with moderate acoustic damping properties. While this invention is significant in highlighting the utility of banana fibers for dual insulation purposes, it does not describe the integration of recycled synthetic fibers such as rPET to enhance mechanical stability, density uniformity, or thermal bonding capability. Additionally, optimization of the fiber ratio, panel thickness, or density for maximizing NRC and R-values simultaneously is not disclosed. Therefore, while AU2011251882B2 contributes to the understanding of banana fiber utilization in insulation, it fails to provide a material with synergistic acoustic-thermal performance combined with structural robustness, which forms the basis of the present invention.
EP2628837A1 discloses a nonwoven structure comprising a scrim with a first surface and a second surface, where a polymeric coating is applied to enhance acoustic and thermal insulation properties. The invention focuses on achieving controlled sound absorption and thermal resistance through careful design of the nonwoven web, basis weight (from 8 gsm to 200 gsm), and polymeric overlays. The coated nonwoven exhibits improved mechanical stability and dimensional integrity, making it suitable for wall panels, ceiling liners, and other insulation applications. While this prior art teaches the utility of synthetic coatings to improve insulation, it relies on synthetic polymers alone and does not disclose the use of renewable natural fibers such as banana fibers in combination with recycled PET fibers. Moreover, the material lacks a discussion of synergistic effects arising from a hybrid natural-synthetic fiber web, especially in achieving high NRC alongside thermal insulation. Therefore, while EP2628837A1 demonstrates advances in coated nonwovens, it does not anticipate the eco-friendly, hybrid, high-performance composite of the present invention.
JP5827980B2 describes non-woven materials for soundproofing, utilizing multicomponent fibers with reversible thermal properties. The invention focuses on providing effective acoustic damping in automotive interiors, industrial enclosures, and construction applications. The disclosed fibers are processed into nonwoven mats with controlled density and porosity, allowing absorption of a broad range of sound frequencies. While this patent addresses soundproofing effectively, the disclosed materials are primarily synthetic in nature and do not combine natural fibers such as banana fibers with recycled PET. Consequently, while mechanical stability and sound absorption are achieved, thermal insulation is not optimized, and environmental sustainability aspects, such as using agricultural waste or recycled fibers, are not considered. Therefore, JP5827980B2 provides relevant teaching on sound absorption using nonwoven mats but fails to provide a hybrid natural-synthetic material exhibiting simultaneous high thermal and acoustic performance.
The study Development of Recycled PET/comber Noil Nonwovens for Thermal Insulation Application explores the use of recycled PET fibers in nonwoven mats for thermal insulation applications, often combined with other natural or synthetic fibers. The research demonstrates that rPET-based nonwovens can achieve good thermal resistance and structural stability, while promoting recycling of post-consumer plastic waste. The process involves airlay or carding, web formation, and thermal bonding to produce panels with controlled GSM and thickness. However, the study focuses on thermal insulation and mechanical performance without exploring the unique acoustic properties imparted by hollow, porous natural fibers such as banana fibers. Furthermore, the possibility of synergistic performance arising from a hybrid combination of banana and rPET fibers is not discussed. While this reference contributes to the understanding of recycled PET fibers in insulation, it does not anticipate the novel hybrid, eco-friendly, acoustic-cum-thermal nonwoven composite provided by the present invention.
While the aforementioned prior arts demonstrate the potential of natural fibers and polymers in insulation materials, they exhibit certain limitations. Many prior art materials focus on either acoustic or thermal insulation but do not achieve a synergistic effect that enhances both properties simultaneously. Some materials rely on synthetic binders or non-renewable resources, limiting their sustainability and biodegradability. Natural fiber-based materials may suffer from mechanical instability, affecting their durability and performance over time.
There is a pressing need for an insulation material that simultaneously exhibits high acoustic and thermal insulation properties, achieving a synergistic effect that enhances both properties beyond the capabilities of individual materials, a material incorporating natural fibers and recycled polymers to reduce environmental impact, a material ensuring its performance over time under various environmental conditions.
The present invention addresses these limitations by providing a hybrid nonwoven composite that combines the unique acoustic and moisture-regulating properties of banana fibers with the structural and thermal advantages of recycled PET fibers. The combination yields a material that is lightweight, mechanically robust, flame-retardant, moisture-regulating, and environmentally sustainable, filling a gap in prior art by achieving simultaneous high-acoustic performance, mechanical integrity, thermal insulation, and eco-friendliness.
OBJECTIVES OF THE INVENTION
• The primary objective of the present invention is to provide a hybrid nonwoven composite material comprising banana fibers derived from agricultural waste and recycled polyethylene terephthalate (rPET) fibers, which exhibits simultaneously high acoustic absorption and thermal insulation properties.
• Another objective of the present invention is to develop a composite material that utilizes renewable natural fibers and recycled synthetic fibers, thereby contributing to environmental sustainability and circular economy practices.
• Yet another objective of the present invention is to achieve a material with enhanced Noise Reduction Coefficient (NRC) values, particularly in the frequency range of 100 Hz to 6300 Hz, suitable for industrial, automotive, building, and consumer applications.
• Yet another objective of the present invention is to provide a composite exhibiting improved mechanical strength and dimensional stability, overcoming the weaknesses of pure natural fiber mats, while maintaining lightweight characteristics for ease of handling and installation.
• Yet another objective of the present invention is to enable customization of composite panels in terms of thickness, grams per square meter (GSM), and fiber blend ratios, so as to tune acoustic and thermal properties for specific application requirements.
• Yet another objective of the present invention is to provide a manufacturing process for forming a homogeneous, mechanically stable web, through techniques such as carding, blending, web laying (dry-laid), thermal bonding, and optional needle punching, thereby ensuring consistent quality at industrial scale.
• Yet another objective of the present invention is to offer multi-layered composite embodiments, wherein inner and outer layers contain different fiber ratios, thereby optimizing low-frequency and high-frequency sound absorption without compromising thermal resistance.
• Yet another objective of the present invention is to provide a composite material with optional fire-retardant, moisture-resistant, and surface-finished features, making it suitable for automotive, building, industrial, and consumer applications requiring safety and durability.
• Yet another objective of the present invention is to reduce the environmental footprint associated with conventional acoustic and thermal insulation materials, by utilizing agricultural waste and post-consumer recycled fibers, and providing a fully recyclable or biodegradable product.
• Yet another objective of the present invention is to provide a versatile and cost-effective solution that can be used in automotive interiors, building panels, industrial enclosures, HVAC systems, consumer appliances, and decorative or acoustic textiles, thereby offering a high-performance, sustainable alternative to conventional mineral wool, glass wool, and synthetic foams.
SUMMARY OF THE INVENTION
The present invention relates generally to nonwoven composite materials and more particularly to hybrid composites comprising natural fibers derived from agricultural waste and synthetic fibers recycled from post-consumer waste, configured for high acoustic -performance, thermal insulation, mechanical robustness, and sustainability. Specifically, the invention concerns the development, composition, processing, and applications of natural fibers and recycled fibers hybrid nonwoven composite that exhibits exceptional noise reduction coefficients (NRC), dimensional stability, recyclability, and eco-friendliness.
The agricultural waste-derived banana fibers, due to their hollow cross section, micro-porous cellular structure, and natural hygroscopicity, provide exceptional sound absorption and moisture regulation, particularly in low- to mid-frequency acoustic ranges. However, pure banana fiber mats, although lightweight and sustainable, are inherently mechanically weak and prone to deformation, which limits their application in demanding acoustic and structural environments. To overcome this, the invention incorporates recycled polyethylene terephthalate (rPET) fibers, which are derived from post-consumer or post-industrial PET waste, providing dimensional stability, tensile strength, resilience, and thermal bonding capability.
In an embodiment, the invention synergistically blends 40–70% banana fibers by weight with 25–50% rPET fibers by weight, optimizing the ratio to balance acoustic efficiency, mechanical performance, and thermal properties. The resulting nonwoven composite demonstrates a Noise Reduction Coefficient (NRC) 0.50 to 0.98 across a frequency range of 250–6300 Hz, a level of acoustic performance that is comparable or superior to conventional synthetic and mineral fiber panels while maintaining lower density and improved environmental sustainability.
The banana fibers employed are mechanically extracted from banana pseudostem, washed, and dried to remove impurities, then cut to lengths ranging from 25–60 mm and denier of 10–70. The fibers possess a natural hollow Cross section, with micro-porous cell walls contributing to sound energy dissipation. The rPET fibers are obtained from recycled PET bottles or industrial PET waste, opened to staple lengths of 25–60 mm and deniers of 0.9–15, facilitating thermal bonding at 120–220 °C during composite formation.
Blend ratios are carefully optimized through experimental trials. A higher proportion of banana fibers enhances absorption of low - high frequencies and moisture regulation, whereas higher rPET content improves surface strength, dimensional stability, and thermal bonding efficiency. The composite web is formed with a grams-per-square-meter (GSM) ranging from 200–2500 g/m², and thickness adjustable between 9–80 mm, depending on application requirements. Porosity is controlled to maximize acoustic energy dissipation while maintaining mechanical integrity.
In another embodiment, the manufacturing process of the hybrid nonwoven composite comprises sequential steps:
• Fiber Opening and Cleaning: Banana fibers are mechanically opened, washed, and dried. rPET fibers are similarly opened to separate individual filaments.
• Carding and Blending: Individual fibers are aligned via carding and then blended in the predetermined ratio to form a homogenous web.
• Web Formation: The blended fibers are formed into a continuous web using air-laid, carding, or layered deposition techniques, ensuring uniform thickness and density.
• Bonding and Consolidation: The web is consolidated using thermal bonding where rPET fibers partially melt and interlock with banana fibers. Optional needle punching provides additional mechanical strength and flexibility.
• Finishing: Post-processing steps, including calendaring, trimming, lamination, coating, or flame-retardant treatment, are applied to meet application-specific performance requirements.
The manufacturing process is scalable, enabling consistent production of uniform composite panels suitable for automotive, construction, industrial, and consumer applications.
In yet another embodiment, the invention encompasses multiple technical variations and embodiments to tailor performance for specific applications:
In yet another embodiment, the invention employes thermal bonding for enhanced dimensional stability; needle punching for flexible panels.
In yet another embodiment, the invention employes composite panels with varied banana/rPET ratios across layers to optimize frequency-specific acoustic absorption and surface rigidity.
In yet another embodiment, the invention employs moisture conditioning or bio-based treatment to enhance fiber entanglement.
In yet another embodiment, the invention employs calendaring, lamination, coating, or chemical treatment to enhance surface smoothness, moisture resistance, fire safety, and aesthetic finish.
In yet another embodiment, the present invention provides a unique material that synergistically combines the intrinsic acoustic properties of natural banana fibers with the structural and thermal benefits of rPET fibers, resulting in enhanced overall acoustics and thermal performance that is unobtainable by either fiber alone or in any other combination. The synergistic performance of the composite extends to a variety of applications, including automotive interiors such as door panels, dashboards, headliners, and trunk liners; building interiors such as walls, ceilings, floors, and partitions; industrial applications including machinery enclosures, HVAC ducts, and acoustic barriers; as well as consumer appliances including air conditioners and washing machines. The composite can be tailored in thickness, GSM, and fiber composition to meet the specific acoustic and thermal requirements of each application, thereby providing a versatile, high-performance, and sustainable insulation solution.
BRIEF DESCRIPTION OF DRAWINGS:
For a complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:
Figure 1 illustrates a schematic flow diagram of the process for manufacturing the acoustic and thermal insulating nonwoven composite, showing stages including fiber blending, opening, carding, cross-lapping, bonding, calendaring, winding and cutting.
Figure 2 presents a graphical representation of acoustic performance (NRC) versus frequency for the composite material.
Figure 3 presents a graphical representation of thermal performance (R-value) versus composite thickness, demonstrating tunable thermal insulation properties.
Figure 4 depicts SEM images of composite material
Figure 5 illustrates sheet of nonwoven composite
Figure 6 illustrates applications of the nonwoven composite in architectural acoustics.
DETAILED DESCRIPTION OF THE INVENTION
The present invention shall now be described in detail with reference to numerous embodiments, examples, and optional variations, it being expressly understood that the scope of the invention is not limited to the embodiments so described, but extends to all modifications, equivalents, alternatives and adaptations that fall within the purview of a person skilled in the art. The purpose of this detailed description is to enable full and sufficient disclosure of the invention in the manner required under the Patents Act, 1970, and more particularly under Section 10(4) of the said Act, while simultaneously placing before the skilled artisan a disclosure that allows reproduction and practice of the invention at an industrial scale.
To facilitate the understanding of this invention, several terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as “a”, “an” and “the” are not intended to refer to only a singular entity but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not delimit the invention, except as outlined in the claims.
Natural fibers are fibrous raw materials directly from plant, animal, or mineral sources, used to create textiles, ropes, and other products by spinning them into yarns or forming them into nonwoven materials like paper or felt.
Recycled fibers are textile materials derived from waste, transforming post-consumer or post-industrial waste into new usable fibers for products like clothing, home furnishings, and insulation. Common examples include recycled polyester (rPET) from plastic bottles and recycled cotton or wool from textile waste.
Banana fibres are lignocellulosic fibres obtained from the pseudostems of banana plants, typically comprising cellulose, hemicellulose, lignin, and minor phosphorus compounds; having a length of about 25–60 mm and denier ranging between 10–70.

Recycled PET fibres (rPET) are synthetic polyester fibres obtained by reprocessing post-consumer or post-industrial PET waste, including but not limited to PET bottles, films, or preform scraps; having a staple length of about 25–60 mm and denier of 0.9–15.
Low-melt PET fibres are modified polyester fibres characterised by a reduced melting temperature (typically 90 –150 °C), employed as thermal bonding fibres to achieve inter-fibre cohesion.
Nonwoven composite is fibrous structure produced without weaving or knitting, obtained by entanglement and bonding of fibres into a web; herein comprising banana fibres and rPET fibres in defined ratios.
Noise Reduction Coefficient (NRC) is the arithmetic average of the absorption coefficients at 250 Hz, 500 Hz, 1000 Hz, and 2000 Hz, representing the material’s ability to absorb sound.
Thermal Conductivity (k) is the rate at which heat passes through a material, expressed in W/m·K.
R-value is a measure of thermal resistance of a material, calculated as thickness divided by thermal conductivity (m²·K/W).
GSM (grams per square metre) is a real density of the nonwoven fabric.
Dimensional stability is ability of the nonwoven composite to retain its shape and structure under mechanical or thermal stress.
The invention relates to a sustainable nonwoven composite comprising natural fibres derived from agricultural waste such as banana, coir, jute, hemp, cotton, kapok, linen, sisal, pineapple, wool, mohair, alpaca in conjunction with recycled fibers such as polyethylene terephthalate (rPET), acrylic, polypropylene, nylon, polyethylene, cotton, wool, jute, coir, optionally further comprising low-melt binding fibers and/or other natural fibres such as wool, jute, coir, or cotton. The hybrid nonwoven composite of the present invention is specifically engineered for high acoustic absorption, thermal insulation, dimensional stability, and environmental sustainability, thereby addressing limitations prevalent in conventional insulating materials.
While numerous materials for insulation and noise attenuation exist in the prior art, these are often beset with disadvantages including environmental unsustainability, reliance on virgin petrochemical resources, health hazards, and recycling limitations. The present invention departs from the conventional approach by employing renewable banana fibres, which are otherwise discarded as agro-waste, in combination with post-consumer recycled fibres, thereby valorising two waste streams into a technically advanced product. The composite of the invention further integrates tailored manufacturing processes including fibre opening, blending, web formation, cross-lapping, thermal bonding, and/or needle punching, to produce a homogeneous, mechanically stable, and recyclable panel with tailored GSM, thickness, and acoustic-thermal properties.
The invention is thus simultaneously ecological and industrial in character: ecological, in the sense that it utilises waste streams and reduces carbon footprint; and industrial, in that it can be manufactured using established nonwoven technologies at scale, with predictable and reproducible results.
In one embodiment, the invention relates to a sustainable nonwoven composite material comprising a mixture of banana fibres derived from agricultural waste pseudostems and recycled polyethylene terephthalate (rPET) fibres obtained from post-consumer or post-industrial waste. The composite is engineered to deliver synergistic acoustic and thermal insulating performance, while also being lightweight, recyclable, partially biodegradable, and industrially scalable.
In another embodiment, the invention provides a hybrid fibrous web where the hollow, micro-porous, and flame-resistant banana fibres are intermingled with the mechanically resilient, thermally bondable rPET fibres to form a nonwoven structure that exhibits high noise reduction coefficient (NRC), excellent R-value, structural integrity, and environmental sustainability.
In yet another embodiment, the invention contemplates multi-layered composites exhibits different ratios of banana fibres, rPET fibres, and optionally low-melt PET fibres or other natural fibres such as wool, jute, coir, or cotton, thereby permitting frequency-specific sound absorption and application-tailored thermal insulation.
In one embodiment, the banana fibres are obtained from banana pseudostems, which are otherwise discarded as agricultural waste. The fibres are mechanically extracted, washed, dried, cut, and carded to yield material suitable for nonwoven formation.
Fibre length: about 25–60 mm; longer fibres improve entanglement and web cohesion.
Denier: about 10–70; influencing flexibility and surface area.
Moisture content: about 8–12% after processing, ensuring stability.
Cross-section: naturally hollow and micro-porous, facilitating acoustic energy dissipation.
Chemical composition: lignocellulosic, with natural phosphorus-containing compounds contributing to inherent flame retardancy.
In another embodiment, the banana fibres may be surface treated (for example by alkaline treatment, enzymatic treatment, or moisture conditioning) to improve compatibility with rPET fibres and to enhance fibre migration during carding.
In one embodiment, rPET fibres are obtained from recycled PET bottles, films, or industrial PET waste. These fibres impart dimensional stability, tensile strength, and resilience to the composite.
Fibre length: about 25-60 mm.
Denier: about 0.9–15.
Softening point: about 250°C, allowing for thermal bonding without chemical binders.
In yet another embodiment, rPET fibres serve as structural reinforcement while also enabling thermal fusion at bonding stages, thereby eliminating the need for synthetic adhesives.
In one embodiment, low-melt PET fibres are incorporated in the blend, typically in the range of 10–25% by weight. These fibres have a melting temperature between 90–150°C and facilitate inter-fibre cohesion during through-air or calendaring processes, improving dimensional stability, loft, and surface smoothness.
In certain embodiments, the invention further comprises other natural fibres such as:
i. Wool fibres for enhanced acoustic absorption and surface softness.
ii. Jute fibres for cost-effectiveness and bulk density adjustment.
iii. Coir fibres for resilience and elasticity.
iv. Cotton fibres for softness and hand feel.
These additional fibres may be present in amounts ranging from 5–30 wt% depending on the application.
In one embodiment, the blend comprises:
Banana fibres: 40–70 wt%
rPET fibres: 25–50 wt%
Optional low-melt PET fibres: 10–25 wt%
Optional other natural fibres: 5–30 wt%
In another embodiment, a preferred blend ratio of 1:4 to 4:1 (natural fibres and recycled fibres) exhibits an NRC of 0.98 and an R-value > 2.0, as determined by impedance tube and guarded hot plate testing.
In another embodiment, a preferred blend ratio of 45:30:25 (banana:rPET:low-melt PET) at 1500 GSM exhibits an NRC of 0.98 and an R-value up to 2.0, as determined by impedance tube and guarded hot plate testing.
In yet another embodiment, the composite may be tailored for specific end-use:
i. Higher banana fibre ratio: improved sound absorption at low–mid frequencies.
ii. Higher rPET ratio: improved structural rigidity and bonding strength.
iii. Higher low-melt PET ratio: improved surface finish and dimensional stability.
In one embodiment, the nonwoven composite comprises a single homogeneous web where banana fibres and rPET fibres are uniformly blended and bonded.
In yet another embodiment, the composite may comprise homogeneous fibre distribution across thickness, thereby optimising absorption at both low and high frequencies.
In one embodiment, the composite has:
Basis weight (GSM): 500–2000 g/m².
Thickness: 9–50 mm.
In another embodiment, thinner panels (9–20 mm) are suited for consumer appliances and interior trims, while thicker panels (30–80 mm) are suited for building insulation and industrial enclosures.
In yet another embodiment, multi-layer laminates can be constructed, where each layer is tailored in GSM and thickness for specific performance.
In one embodiment, the composite exhibits:
Noise Reduction Coefficient (NRC): 0.50 to 0.98 across 100-6300 Hz.
Thermal conductivity (k): 0.030–0.045 W/m·K.
R-value: 1.2–2.0 depending on thickness.
Dimensional stability: retained after repeated compression cycles.
Limiting oxygen index (LOI) of 20 to 28 providing fire retardancy of class-1 fire rating (IS-11871, EN 13501)
In another embodiment, the composite uses chemical free binder, for cohesion along with thermal bonding and/or needle punching to maintain structural integrity and thereby ensuring recyclability and eco-friendliness.
In yet another embodiment, the composite exhibits inherent antimicrobial activity with inhibition zones >25 mm against common microbial pathogens such as Escherichia coli and Aspergillus niger.
In one embodiment, the invention provides a dry-laid nonwoven manufacturing process, wherein banana fibres and recycled PET fibres are blended, carded, and formed into webs, followed by bonding and finishing operations to obtain composite panels of desired GSM and thickness.
In another embodiment, the invention contemplates industrial-scale carding, cross-lapping, and bonding techniques, enabling uniform fibre distribution and mechanical stability. The process is compatible with existing nonwoven production lines, thereby ensuring industrial scalability and cost-effectiveness.
In yet another embodiment, the invention contemplates multi-step processing sequences wherein fibres are first pre-treated, then opened and blended, before undergoing web formation and bonding.
In one embodiment, banana fibres are obtained from banana pseudostem by mechanical extraction. The fibres are then:
• Washed to remove residual pith, gums, and impurities.
• Dried under controlled conditions to achieve a moisture content of about 8–12%.
• Cut to desired length, typically 30–60 mm.
• Optionally subjected to alkaline treatment or enzyme treatment to improve surface roughness and compatibility with thermoplastic fibres.
In another embodiment, a wetting or moisture-conditioning step is performed prior to carding to enhance fibre migration, reduce fibre breakage, and improve entanglement with rPET fibres.
In one embodiment, recycled PET fibres are derived from post-consumer PET bottles. The process involves:
• Collection and sorting of PET waste.
• Washing and removal of labels and caps.
• Mechanical shredding and re-extrusion into PET chips.
• Fibre spinning into staple lengths of 25–35 mm.
• Bale formation for subsequent nonwoven processing.
In yet another embodiment, the rPET fibres are surface treated with dispersing agents to reduce static and improve compatibility with banana fibres.
In one embodiment, low-melt PET fibres are included at 10–25% by weight. These fibres are spun with modified polymer chemistry to reduce the softening temperature to 90–150 °C, enabling bonding without damaging natural fibres.
In one embodiment, fibres are opened in a two-stage opener system, comprising a pre-opener and a fine-opener.
• The pre-opener teases apart fibre clumps.
• The fine-opener separates fibres to near-individual state.
In another embodiment, banana fibres and rPET fibres are weighed and blended in predetermined ratios (e.g., 45:30:25 banana:rPET:low-melt PET). The blending may be performed:
• Manually, in small batches for laboratory trials.
• Mechanically, using hopper belnders and conveying systems for industrial runs.
In yet another embodiment, the invention contemplates continuous blending systems wherein fibres are metered and conveyed synchronously to maintain ratio uniformity throughout web formation.
In one embodiment, blended fibres are fed into carding machines where:
• Fibres are aligned.
• A uniform web is formed.
• GSM and thickness are controlled by doffer speed and feed roller speed.
In another embodiment, cross-lapping is employed to lay multiple layers of carded web transversely, thereby improving uniformity and isotropy of the final nonwoven.
In one embodiment, dry laid technology is used to disperse fibres pneumatically, yielding low-density, high-loft webs with superior acoustic absorption.
In another embodiment, wet-laid processing is contemplated for shorter banana fibres (<20 mm), where fibres are suspended in an aqueous medium, deposited on a screen, and dewatered to form a mat.
In one embodiment, thermal bonding is achieved using:
• Through-air bonding: hot air is circulated through the fibre web, melting the low-melt PET component while retaining rPET and banana fibre structure.
• Calendar bonding: heated rollers compress the web under pressure, imparting smoothness and compactness.
In another embodiment, bonding parameters such as temperature (120–220°C), dwell time, and airflow rate are precisely controlled to achieve sufficient inter-fibre cohesion without degradation of banana fibres.
In one embodiment, needle punching is employed as an alternative or supplementary bonding method.
• Barbed needles entangle fibres mechanically.
• Webs achieve dimensional resilience and tensile strength.
• Particularly useful where low GSM (200–1000) composites are required.
In yet another embodiment, a hybrid bonding method combines thermal bonding and needle punching, yielding a balance of softness, stability, and porosity.
In one embodiment, the bonded composite may be subjected to calendaring to adjust surface density and smoothness.
In another embodiment, lamination with films or fabrics may be employed for decorative or protective applications.
In yet another embodiment, coatings or surface treatments may be applied, including:
• Fire-retardant coatings (optional, since banana fibres have inherent resistance).
• Hydrophobic finishes for moisture resistance.
• Antimicrobial coatings to augment inherent activity.
Optional Process Variations
• In one embodiment, multi-layer composites are produced by sequential deposition of different fibre blends, each optimized for acoustic, thermal, or mechanical properties.
• In another embodiment, embossing or patterning is applied during calendaring to improve aesthetic appeal and airflow resistance tuning.
• In yet another embodiment, bio-based resins or binders (such as polylactic acid) may be optionally introduced, provided recyclability is maintained.
In one embodiment, quality control is achieved by monitoring:
• Web uniformity using optical scanning.
• Basis weight consistency via gravimetric checks.
• Bonding adequacy through tensile and peel strength tests.
In another embodiment, process data such as airflow, roller temperature, and needle density are digitally logged, allowing traceability and repeatability.
Examples:
The following examples illustrate the embodiments of the present invention and the methods for preparing and testing the sustainable nonwoven composite comprising banana fibres and recycled polyethylene terephthalate (rPET) fibres. These examples are provided for explanatory purposes only, and it shall be expressly understood that the scope of the invention is not limited thereby. Variations in raw material selection, fibre length, denier, blending ratios, bonding methods, and finishing steps are all contemplated as falling within the scope of the invention.
Example 1 – Selection and Preparation of Banana Fibres
In one embodiment, banana fibres were mechanically extracted from pseudostems collected as agricultural waste after harvesting of the crop.
• Extraction: Performed by mechanical decortication, yielding long continuous fibres.
• Cleaning: Fibres washed in alkaline solution (2% NaOH) to remove waxes and pectins, followed by rinsing in water.
• Drying: Oven-dried at 60 °C until moisture content reduced to about 8–12%.
• Cutting: Long fibres cut into staple lengths ranging from 25–60 mm.
• Carding: Pre-carded to facilitate blending with synthetic fibres.
The banana fibres exhibited hollow structures and micro-porous cell walls, providing excellent potential for sound energy absorption.
Example 2 – Preparation of Recycled PET Fibres
In another embodiment, rPET fibres were obtained from post-consumer PET bottles.
• Bottles were collected, sorted, washed, and shredded.
• Shredded flakes were dried and re-extruded into PET chips.
• PET chips were spun into staple fibres of 25–35 mm length and 0.9–15 denier.
• Bale packing ensured ease of handling.
The rPET fibres demonstrated tensile resilience and softening temperature around 250 °C, making them ideal for thermal bonding with banana fibres.
Example 3 – Blend Optimisation Trials
A series of blend compositions were prepared to determine optimum ratios for acoustic and thermal performance.
• Trial A: 20–25 mm banana fibres blended with 25–35 mm rPET fibres.
o Result: Poor fibre entanglement, irregular web GSM.
o Carding efficiency: ~34%.
• Trial B: 30–35 mm banana fibres blended with 25–35 mm rPET fibres.
o Result: Improved bulk, moderate web uniformity.
o Carding efficiency: ~51%.
• Trial C: 40–60 mm banana fibres blended with 25–35 mm rPET fibres.
o Result: Excellent fibre entanglement, high processing efficiency.
o Carding efficiency: ~67%.
The data confirmed that longer banana fibres (40–60 mm) improved web cohesion and overall dimensional stability.
Example 4 – Nonwoven Process Finalisation
In one embodiment, dry-laid carding and cross-lapping was selected as the most suitable web formation process.
• Alternative methods such as spunbond, melt-blown, and wet-laid were tested but found less compatible with long banana fibres.
• Bonding techniques compared:
o Through-air thermal bonding: yielded soft, lofted composites.
o Calendaring: imparted surface smoothness.
o Needle punching: enhanced mechanical strength at lower GSM.
The optimal process was identified as dry-laid carding + cross-lapping + thermal bonding, optionally supplemented by needle punching.
Example 5 – Optimised Blend Ratio
Multiple blend ratios were tested at different GSM values.
• Blend 60:20:20 (Banana:rPET:Low-melt PET): Good stability, NRC ~0.80.
• Blend 35:40:25: Balanced performance, NRC ~0.85.
• Blend 45:30:25 at 1500 GSM: Outstanding results, NRC 0.50 - 0.98, R-value >2.0.
Thus, the preferred embodiment was identified as 45:30:25 at 1500 GSM for high-performance acoustic and thermal insulation.
Example 6 – Incorporation of Other Natural Fibres
In one embodiment, banana fibres were blended with wool and low-melt PET.
• Blend ratios tested: 30:30:40, 0:40:60, 50:15:35.
• GSM: 1000.
• Thickness: ~40 mm.
The resulting nonwovens exhibited NRC values of 0.50 - 0.98 in mid to high frequency ranges (100–6300 Hz), and an R-value of >2, suitable for interior textile applications.
Example 7 – Comparative Results
The performance of various composites is tabulated below:
S.N. Material Bonding Method GSM Noise Reduction Coefficient Thickness(mm) Thermal Conductivity
(w/mk)
1 Banana+R-PET Thermal Bonding 1000 0.725 30.68 0.037
2 Banana+R-PET Thermal Bonding 1500 0.8975 34.62 0.034
3 Banana+R-PET Thermal Bonding 500 0.5722 14.77 0.042
4 Wool Thermal Bonding 1000 0.6525 41 0.038
5 Wool Thermal Bonding 1500 0.7525 47.08 0.038
6 Wool + Banana Thermal Bonding 1000 0.6925 35.4 0.037
7 Wool + Banana Thermal Bonding 1500 0.83 45.22 0.039
8 Banana +R-PET Thermal Bonding 2000 0.857 31.78 0.034
9 Banana+R-PET Needle punched + Thermal Bonded 1000 0.4775 6.076 0.050
10 Banana+R-PET Needle punched + Thermal Bonded 1500 0.7275 9.396 0.038
11 Wool Needle punched + Thermal Bonded 1000 0.565 8.646 0.038
12 Wool Needle punched + Thermal Bonded 1500 0.765 11.38 0.041
13 Wool+R-PET Needle punched + Thermal Bonded 500 0.5782 13.95 0.039
14 Wool+R-PET Needle punched + Thermal Bonded 2000 0.8261 28.64 0.035
15 Wool + Banana Needle punched + Thermal Bonded 1000 0.5225 7.706 0.038
16 Wool + Banana Needle punched + Thermal Bonded 1500 0.75 10.916 0.040

The data establishes that the Banana:rPET:Low-melt PET blend at 1500 GSM achieved superior NRC and thermal insulation properties compared to wool-based or needle-punched variants.
Example 8 – Product Specification
In one embodiment, composite panels were produced with the following specifications:
• Dimensions: 8 × 4 feet (customisable).
• Composition: Banana fibre + rPET fibre (optionally with wool).
• GSM: 500–2000.
• Thickness: 9, 20, 30, 40, 50 mm.
• Light fastness (ISO 105-B02-1994): >7.
• Fire protection (EN 13501 / IS-11871): Class 1 non-flammable.
• Antimicrobial index: >25 mm zone of inhibition.
• NRC: 0.50 - 0.98.
• Thermal conductivity: 0.030–0.045 W/m·K.
• R-value: up to 2.0.
• Limiting oxygen index (LOI): of 20 to 28 providing fire retardancy of class-1 fire rating (IS-11871, EN 13501)
In one embodiment, the invention provides a sustainable, high-performance nonwoven composite suitable for applications where noise control, thermal insulation, and structural stability are simultaneously required. The material is lightweight, easy to handle, chemical binder free, and recyclable, making it particularly attractive for industries seeking compliance with environmental sustainability goals.
In another embodiment, the invention contemplates use across automotive, architectural, industrial, HVAC, and consumer appliance sectors, wherein the hybrid structure of banana fibres and recycled PET fibres yield a versatile alternative to conventional mineral wool, glass wool, polyurethane foams, or virgin polyester mats.
In one embodiment, the nonwoven composite is employed in door panels, dashboards, roof headliners, floor insulations, trunk liners, and wheel arch covers. The composite demonstrates NRC values 0.50 - 0.98, reducing cabin noise from engine, road, and wind sources. The lightweight nature reduces overall vehicle weight, contributing to fuel efficiency and reduced emissions.
In another embodiment, the composite improves thermal insulation inside the passenger cabin, maintaining cooler interiors in hot climates and reducing air-conditioning loads. Fire safety is enhanced due to the inherent flame-resistant nature of banana fibres, thereby reducing reliance on toxic flame retardants. The composite remains stable under vibration and repeated compression, suitable for long-term automotive usage.
In yet another embodiment, the composite can be processed into pre-cut panels compatible with existing automotive moulding and lamination lines. Adhesive-free bonding allows easy recycling of end-of-life vehicles, aligning with Extended Producer Responsibility (EPR) regulations.
In one embodiment, the composite is configured into acoustic wall panels, ceiling tiles, baffles, and room partitions. NRC values 0.50 to 0.98 make it suitable for theatres, auditoriums, conference halls, and recording studios. The bio-based fibre structure provides a warm aesthetic and tactile quality, differentiating it from synthetic acoustic foams.
In another embodiment, the composite serves as thermal insulation boards in walls, roofs, and floors. R-values up to 2.0 is achieved to enable energy savings in HVAC usage. The composite resists sagging and compression, unlike glass wool or PU foam.
In yet another embodiment, the composite exhibits limiting oxygen index (LOI) of 20 to 28 providing fire retardancy of class-1 fire rating (IS-11871, EN 13501). This makes it appropriate for public buildings, schools, hospitals, and offices, where fire safety standards are mandatory.
In one embodiment, the composite is employed in noise control enclosures for industrial machinery such as compressors, generators, and stamping presses. The composite dampens both low-frequency vibrations and high-frequency noise. Panels remain dimensionally stable even under elevated operating temperatures.
In another embodiment, the composite is integrated into air-handling units, duct liners, and diffusers. It provides sound attenuation in ductwork. Thermal resistance improves energy efficiency by reducing losses in cooled or heated air. The antimicrobial index >25 mm ensures resistance against microbial growth in moist HVAC environments.
In one embodiment, the composite is incorporated into washing machines, dishwashers, refrigerators, and microwave ovens. In washing machines, it reduces operational vibration and acoustic emission. In dishwashers, it provides thermal insulation to improve energy efficiency. In refrigerators, it maintains temperature stability and reduces compressor noise. In microwave ovens, it provides acoustic damping for quieter operation.
In another embodiment, the composite is shaped into removable insulation panels for appliances, allowing recyclability and ease of maintenance.
In one embodiment, the composite is suitable for railway carriages, buses, and ships, where noise reduction and thermal comfort are critical. In railway applications, it reduces rolling noise and cabin vibration. In buses, it acts as roof liners, wall panels, and floor insulation, improving passenger comfort. In ships and marine vessels, the composite provides acoustic insulation, leveraging the inherent hydrophobicity of PET fibres.
In another embodiment, aerospace interior panels may utilise the composite due to its lightweight structure and fire-resistant nature, reducing reliance on hazardous foams.
The composite of the present invention demonstrates multiple advantages over conventional materials across applications:
• Unlike glass wool, it does not produce harmful fibrogenic dust.
• Unlike polyurethane foams, it is partially biodegradable, recyclable and fire retardant.
• Unlike pure natural fibres, it retains dimensional stability and tensile strength.
• Unlike adhesive-based composites, it can be recycled easily since bonding is physical and not chemical.
In one embodiment, the invention provides an industrially scalable process that leverages agro-waste (banana pseudostem) and post-consumer plastics (PET bottles).
• The process is compatible with existing nonwoven manufacturing lines with only minor modifications.
• The resulting product is cost-competitive while offering superior NRC and R-values.
• It contributes to the circular economy by diverting waste from landfills and providing new revenue streams for farmers.
In another embodiment, the invention directly addresses global environmental regulations concerning plastics recycling, carbon footprint reduction, and sustainable practices.
Thus, the invention possesses clear industrial applicability in accordance with the requirements of Section 2(1)(ac) of the Indian Patents Act, 1970.
, C , Claims:We Claim:
1. A sustainable nonwoven composite material for high acoustic and thermal insulation comprising natural fibres and recycled fibres.
2. The composite material as claimed in claim 1, wherein the natural fibers are selected from banana, coir, jute, hemp, cotton, kapok, linen, sisal, pineapple, wool, mohair, alpaca, and recycled fibres are selected from polyethylene terephthalate (rPET), acrylic, polypropylene, nylon, polyethylene, cotton, wool, jute, coir.
3. The composite material as claimed in claim 1, wherein the natural fibres are present in the range of 20–70 wt.% and recycled fibres are present in the range of 25–50 wt.%.
4. The composite material as claimed in claim 1, wherein the composite exhibits a noise reduction coefficient (NRC) 0.50 to 0.98 and a thermal conductivity in the range of 0.030–0.045 W/m·K.
5. The composite material as claimed in claim 1, wherein the composite material optionally comprising low-melt recyclable binder present in the range of 10–25% by weight of the total blend to facilitate thermal bonding and dimensional stability.
6. The composite material as claimed in any of the preceding claims, wherein the basis weight of the nonwoven composite is in the range of 500–2500 g/m² and thickness is in the range of 9–80 mm.
7. The composite material as claimed in any of the preceding claims, wherein the material is configured as a multilayer structure having homogenously blended recycled fibres for dimensional stability and natural fibres for acoustic and thermal absorption.
8. The composite material as claimed in claim 1, wherein the natural fibres have a length of 25–60 mm and a denier of 10–70.
9. The composite material as claimed in claim 1, wherein the recycled fibres have a length of 25–60 mm and a denier of 0.9–15.
10. The composite material as claimed in claim 1-8, wherein the composite blend ratio is 1:4 to 4:1 of natural fibres and recycled fibres respectively.
11. The composite material as claimed in claim 1, wherein the composite exhibits antimicrobial activity with an inhibition zone greater than 25 mm to ensure resistance against microbial growth in moist HVAC environments.
12. The composite material as claimed in claim 1, wherein the composite exhibits limiting oxygen index (LOI) of 20 to 28 providing fire retardancy of class-1 fire rating (IS-11871, EN 13501) suitable for public buildings, schools, hospitals, and offices, where fire safety standards are mandatory.
13. A process for preparing a sustainable nonwoven composite material from banana fibers and recycled polyethene terephthalate (rPET), comprising:
• extracting banana fibres from pseudostem, washing, drying, and cutting the fibres into staple lengths of 25–60 mm;
• obtaining recycled PET fibres from post-consumer PET bottles and apparel and cutting them into staple lengths of 25–60 mm;
• blending the banana fibres and rPET fibres in predetermined proportions;
• forming a fibrous web by carding and cross-lapping; and
• bonding the web thermally and/or by needle punching to obtain the nonwoven composite material.
14. The process as claimed in claim 10, wherein the blend further comprises low-melt PET fibres having a melting temperature of 90–150 °C to achieve thermal bonding.
15. The process as claimed in any of claims 10–11, wherein the bonding is performed by thermal bonding at 120–220 °C or calendaring under pressure.
16. The process as claimed in claim 10, wherein the banana fibres are subjected to alkaline or enzymatic surface treatment prior to blending to improve fibre compatibility and adhesion.
17. The process as claimed in claim 10, wherein the blending is carried out in a continuous industrial-scale blow room blending system ensuring uniform weight ratios across the web.
18. The process as claimed in claim 10, wherein the carded web is subjected to cross-lapping to produce a multilayer composite with homogenous distribution of banana and rPET fibres.
19. The process as claimed in claim 10, wherein the web is consolidated by hybrid bonding comprising both thermal bonding and needle punching.
20. The process as claimed in claim 10, wherein finishing operations such as calendaring, coating, embossing, or lamination are applied to improve surface smoothness, dimensional stability, or aesthetics.