Development of sustainable polyurethane materials: a study on the synthesis, properties, and biodegradation of castor oil-based biopolymers

Abstract

Bio-based polyurethanes (PUs) offer a route to reduce fossil-derived plastics. Here, we synthesize castor oil-based PU films via a two-step prepolymer method and systematically vary the NCO/OH ratio (1.0–1.5) and isocyanate structure (aromatic MDI vs. aliphatic HMDI) to elucidate structure–property–biodegradability relationships. Thermal/mechanical behavior (TGA/DSC; tensile testing; hardness), morphology (AFM/SEM), surface wetting, and end-of-life performance (soil burial, 180 d; lipase assay, 28 d) were evaluated. Increasing NCO/OH from 1.0 to 1.5 raised tensile strength from 5.5 to 18.2 MPa and Tonset from 291 to 316 °C, while reducing elongation at break from 352% to 88%. At fixed NCO/OH = 1.2, HMDI-based PU was more extensible (455% vs. 218%), more hydrophilic, and showed greater mass loss than the MDI analog in both soil (35.5% vs. 18.1%) and enzymatic tests (22.1% vs. 9.5%). These data demonstrate that hard-segment content and isocyanate chemistry can be used to tune thermomechanical performance and biodegradation rate in castor-oil PUs, informing sustainable materials design.

Keywords:
castor oil; polyurethane; biodegradation; isocyanates; bio-based polymers

1. INTRODUCTION

The escalating environmental crisis, driven by the accumulation of non-biodegradable waste from petroleum-based plastics, presents one of the most significant challenges of our time. Conventional plastics, such as polyethylene terephthalate (PET) and polypropylene (PP), persist in terrestrial and marine ecosystems for centuries [¹], fragmenting into microplastics and releasing potentially toxic additives [²], thereby posing a severe threat to biodiversity and environmental health. In response, the scientific community has intensified efforts to develop bioplastics, which are polymers derived from renewable biomass sources like plant starches, cellulose, and vegetable oils [³]. These materials offer a sustainable pathway to reduce our dependence on finite fossil fuels [⁴], lower the carbon footprint associated with polymer production [⁵], and design materials with a controlled end-of-life, mitigating long-term pollution. Among the most versatile classes of synthetic polymers are polyurethanes (PUs), whose applications span a vast range of industries, including flexible and rigid foams, coatings, adhesives, elastomers, and medical devices [⁶]. This versatility stems from their unique segmented block copolymer structure, consisting of alternating soft and hard segments, which can be tailored to achieve a wide spectrum of physical and mechanical properties [⁷]. However, the vast majority of commercial PUs are synthesized from petrochemical feedstocks, namely polyols and polyisocyanates, which links them directly to the environmental and economic concerns associated with the fossil fuel industry [⁸]. The development of bio-based PUs is therefore a critical objective for creating a more sustainable polymer economy.

In this context, castor oil (CO), derived from the seeds of Ricinus communis, has emerged as an exceptionally promising renewable feedstock for the synthesis of “green” PUs [⁹]. Unlike other vegetable oils that require chemical modification to introduce hydroxyl functionalities, castor oil is unique in that it is a natural polyol. Its triglyceride structure is predominantly composed of ricinoleic acid, which contains a secondary hydroxyl group on the C-12 position of its fatty acid chain. This inherent functionality, with an average of 2.7 hydroxyl groups per molecule, allows castor oil to react directly with isocyanates to form a polyurethane network, simplifying the synthesis process and enhancing its green credentials. Despite this advantage, PUs synthesized directly from neat castor oil often exhibit limited mechanical strength and thermal stability [¹⁰], necessitating strategic formulation and structural modifications to meet the demands of high-performance applications.

Prior research on castor-oil-based polyurethanes (CO-PUs) has shown that formulation and segmental chemistry can modulate properties, yet most reports examine either mechanical/structural behavior or isolated biodegradation modalities rather than establishing integrated structure–property–degradation relationships. For example, cellulose-modified CO-PUs improved mechanical response and altered microbial susceptibility but did not map degradation outcomes against systematically varied hard-segment content or isocyanate structure [¹¹]; hybrid polyol strategies (e.g., CO/PCL) enhanced flexibility and enzymatic degradability but focused primarily on coating performance [¹²]; and recent bio-based systems demonstrated soil-burial mass loss under greener synthesis routes without resolving how aromatic versus aliphatic isocyanates impact end-of-life behavior [¹³]. Enzyme-assisted depolymerization studies further underscore the role of chemical architecture in polyurethane hydrolysis, but have largely addressed adhesive formulations rather than CO-PU networks [¹⁴]. Here, we explicitly address these gaps by: (i) systematically varying the NCO/OH molar ratio (hard-segment content) and the isocyanate type (aromatic MDI vs. aliphatic HMDI) in CO-PUs; (ii) correlating thermomechanical, morphological, and surface-wetting properties with formulation; and (iii) quantifying end-of-life performance via 180-day soil burial and 28-day lipase assays. The novelty of this study lies in establishing coupled structure–property–biodegradability relationships for CO-PUs and demonstrating how isocyanate chemistry and hard-segment content can be strategically tuned to deliver sustainable polyurethane materials with targeted performance and controlled environmental lifecycles.

2. MATERIALS AND METHODS

2.1. Materials

Commercial-grade castor oil (CO) with a hydroxyl value of approximately 163 mg KOH/g was procured from Acme-Hardesty. 4,4′-diphenylmethane diisocyanate (MDI, 98%), hexamethylene diisocyanate (HMDI, 99%), and the catalyst dibutyltin dilaurate (DBTDL, 95%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Anhydrous tetrahydrofuran (THF, 99.9%), used as the solvent, was also sourced from Sigma-Aldrich. All chemicals were of analytical grade and were used as received without further purification.

2.2. Synthesis of castor oil-based polyurethanes (CO-PUs)

A series of CO-PU films were synthesized using a two-step prepolymer method to ensure controlled reaction kinetics and structural homogeneity. The general procedure was as follows:

Step 1: NCO-Terminated Prepolymer Formation. The synthesis was conducted in a 500 mL three-necked round-bottom flask equipped with a mechanical stirrer, a reflux condenser, and a nitrogen inlet. A calculated amount of diisocyanate (either MDI or HMDI) was first dissolved in THF under a continuous nitrogen purge to maintain an inert atmosphere and prevent side reactions with atmospheric moisture. The solution was heated to 60 °C with constant stirring at 200 rpm [¹⁵]. Subsequently, a stoichiometric amount of castor oil was added dropwise to the isocyanate solution over a period of 30 minutes. After the addition was complete, the reaction temperature was raised to and maintained at 80 °C for 3 hours to facilitate the formation of the NCO-terminated prepolymer. For each batch, the castor-oil charge was explicitly computed from the measured OHV:

n(–OH) = m_CO × (163/56.1) mmol.

For a target [NCO]/[OH] = r, the required isocyanate is n(NCO) = r × n(–OH); thus m_ISO = (n(NCO)/f_ISO) × M_ISO, where f_ISO = 2 for MDI/HMDI. Table S1 reports the resulting masses (m_CO, m_MDI or m_HMDI, and catalyst) for MDI-PU-1.0/1.2/1.5 and HMDI-PU-1.2.

Step 2: Curing and Film Casting. After the prepolymerization step, the reaction mixture was cooled to 40 °C. A catalytic amount of DBTDL, corresponding to 0.1% of the total weight of the reactants, was added to the flask and stirred vigorously for 5 minutes to ensure uniform distribution [¹⁶]. The resulting viscous solution was then carefully poured into a Teflon-coated mold. The cast film was left at ambient temperature (25 °C) for 24 hours to allow for the slow evaporation of the THF solvent [¹⁷]. Finally, to ensure complete curing and removal of any residual solvent, the film was placed in a vacuum oven and post-cured at 60 °C for 12 hours. The resulting transparent, flexible films were stored in a desiccator prior to characterization.

Two distinct series of CO-PUs were prepared to investigate the influence of key structural parameters:

Series A (Effect of NCO/OH Molar Ratio): To study the effect of hard segment content, three polyurethane films were synthesized using the aromatic diisocyanate MDI. The molar ratio of isocyanate groups to hydroxyl groups ([NCO]/[OH]) was systematically varied at 1.0, 1.2, and 1.5. These samples were designated MDI-PU-1.0, MDI-PU-1.2, and MDI-PU-1.5, respectively. This design allows for a direct assessment of how increasing hard segment concentration impacts the material’s properties.

Series B (Effect of Isocyanate Structure): To evaluate the influence of the isocyanate’s chemical nature, two polyurethane films were synthesized at a fixed [NCO]/[OH] molar ratio of 1.2. One film was prepared using the aromatic MDI (the MDI-PU-1.2 sample from Series A), and the second was prepared using the aliphatic diisocyanate HMDI, designated HMDI-PU-1.2. This series enables a direct comparison between the effects of a rigid aromatic hard segment and a flexible aliphatic hard segment on the final polymer properties.

2.3. Biodegradation evaluation

Soil Burial Test: The biodegradability of the CO-PU films in a natural soil environment was evaluated following a modified ASTM D5988 standard [¹⁸]. Pre-weighed, dry film specimens (2 cm × 2 cm) were buried at a depth of 10 cm in active garden soil with a pH of 6.8 and a moisture content maintained at 25%. The soil containers were kept in a controlled environment at 28 ± 2 °C. Samples were retrieved at 30-day intervals over a total period of 180 days. After retrieval, the samples were carefully cleaned with distilled water to remove adhering soil particles, dried in a vacuum oven at 40 °C to a constant weight, and reweighed to determine the percentage weight loss.

Enzymatic Degradation Test: The susceptibility of the CO-PUs to enzymatic hydrolysis was assessed using lipase, a key enzyme in the degradation of polyesters [¹⁹]. Pre-weighed, dry film specimens (1 cm × 1 cm) were incubated in a phosphate buffer solution (pH 7.4) containing lipase from Candida rugosa at a concentration of 1 mg/mL. The incubation was carried out in a shaking incubator at 37 °C for 28 days. A control group of samples was incubated under identical conditions but in a buffer solution without the enzyme. After 28 days, the samples were removed, washed thoroughly with distilled water, dried to a constant weight, and the percentage weight loss was calculated [²⁰].

3. RESULTS AND DISCUSSION

3.1. Synthesis and structural characterization of CO-PUs

The synthesis of all CO-PU formulations proceeded smoothly, yielding transparent, homogenous, and defect-free films. The successful formation of the polyurethane structure was confirmed through comprehensive spectroscopic and structural analyses.

The chemical structures of the raw materials and the synthesized polyurethanes were investigated using FTIR spectroscopy [²¹]. Figure 1 presents the representative spectra for the precursors (CO, MDI) and the resulting MDI-PU-1.2 polymer. The spectrum of castor oil shows a broad absorption band centered at 3440 cm⁻¹ corresponding to the O-H stretching of its hydroxyl groups [²²], and a strong ester carbonyl (C=O) stretching peak at 1745 cm⁻¹. The MDI spectrum is dominated by the characteristic sharp and intense peak at 2270 cm⁻¹ due to the asymmetric stretching of the isocyanate (-N=C=O) functional group [²³]. Upon polymerization, the spectra of all synthesized PU films exhibited significant changes indicative of urethane linkage formation [²⁴]. Most critically, the sharp NCO peak at 2270 cm⁻¹ completely disappeared in all PU samples, confirming the full consumption of the isocyanate groups and the completion of the polymerization reaction [²⁵]. Concurrently, new absorption bands characteristic of the urethane group emerged [²⁶]. A broad band appeared in the region of 3320–3340 cm⁻¹, attributed to N-H stretching vibrations involved in hydrogen bonding. A prominent C=O stretching peak was observed around 1700–1730 cm⁻¹ [²⁷], and the Amide II band, arising from a coupling of N-H bending and C-N stretching, was present at approximately 1530 cm⁻¹.

Figure 1
Grouped FTIR spectra of CO, MDI, and MDI-PU-1.2.

The shape and position of the urethane carbonyl (C=O) stretching band provide valuable information about the extent of hydrogen bonding within the polymer matrix. This band was deconvoluted into two components: a peak at ~1730 cm⁻¹ corresponding to ‘free’ (non-hydrogen-bonded) carbonyl groups, and a peak at ~1705 cm⁻¹ representing carbonyl groups participating in hydrogen bonds with N-H groups. The formation of these hydrogen bonds between hard segments creates physical cross-links that significantly influence the material’s mechanical properties [²⁸]. It was observed that as the NCO/OH ratio increased in Series A, the relative area of the hydrogen-bonded carbonyl peak increased, signifying a higher degree of intermolecular interaction within the more concentrated hard domains. This molecular-level organization is a direct consequence of the formulation and provides a mechanistic basis for the macroscopic property differences discussed later. To make this analysis explicit, we now report a hydrogen-bonding index (HBI) defined as HBI = A1705/(A1705 + A1730), where A1705 and A1730 are the integrated areas of the hydrogen-bonded and free urethane carbonyl components, respectively. This definition follows established FTIR assignments for segmented PUs (free C=O ≈1730 cm⁻¹; H-bonded C=O ≈1705–1710 cm⁻¹) and enables quantitative comparison across formulations. An increase in HBI with [NCO]/[OH] directly reflects stronger hard-segment association and is consistent with the observed rise in modulus and Tg [²⁹, ³⁰].

The bulk structure of the synthesized polymers was examined by X-ray diffraction [³¹]. Figure 2 displays the XRD patterns for all prepared CO-PU films. Each pattern is characterized by a single, broad amorphous halo centered at a 2θ angle of approximately 20°, with a complete absence of sharp diffraction peaks [³²]. This result confirms that all the synthesized CO-PUs are predominantly amorphous in nature. The lack of crystallinity is attributed to the inherent structural irregularity of the castor oil triglyceride, whose bulky fatty acid chains disrupt long-range periodic packing, and the introduction of urethane linkages, which further hinders chain alignment [³³]. Using Cu Kα radiation, the halo at 2θ≈20° corresponds to d≈4.4 Å (Bragg’s law), which is typical for amorphous segmented polyurethanes and reflects short-range packing within mixed soft/hard domains [³⁴]. The amorphous nature is fundamental to the elastomeric behavior of these materials, as their mechanical integrity relies on chain entanglement and physical cross-links (i.e., hydrogen bonding) rather than reinforcement from crystalline lamellae. This underscores the critical role of hard segment concentration and interaction in determining the material’s final properties [³⁵].

Figure 2
Grouped XRD patterns of MDI-PU-1.0, MDI-PU-1.2, MDI-PU-1.5, and HMDI-PU-1.2.

3.2. Influence of NCO/OH ratio on material properties (Series A: MDI-PUs)

The [NCO]/[OH] molar ratio directly controls the hard segment content in the polyurethane network. By varying this ratio from 1.0 to 1.5 in the MDI-based PU series, we systematically modulated the polymer architecture to establish clear structure-property relationships.

The thermal stability and phase behavior of the MDI-PU series were evaluated using TGA and DSC, with key results summarized in Table 1 [³²]. The TGA and corresponding derivative (DTG) curves are presented in Figure 3. A clear trend was observed: as the NCO/OH ratio increased, both the glass transition temperature (Tg) and the overall thermal stability were enhanced. The Tg increased from -15.8 °C for MDI-PU-1.0 to -2.1 °C for MDI-PU-1.2, and further to 5.3 °C for MDI-PU-1.5. This rise in Tg is a direct result of the increased concentration of rigid MDI-based hard segments, which progressively restrict the segmental mobility of the flexible castor oil soft segment chains.

Table 1
Thermal properties of MDI-PU series a as a function of NCO/OH ratio.

SAMPLE	NCO/OH Ratio	TG (°C)	TONSET (°C)	TMAX (°C)	CHAR RESIDUE @ 700°C (%)
MDI-PU-1.0	1.0	−15.8	291	385	3.1
MDI-PU-1.2	1.2	−2.1	305	402	4.5
MDI-PU-1.5	1.5	+5.3	316	415	6.2

Figure 3
(A) TGA and (B) DTG curves for MDI-PU series.

The TGA results show that all polymers are stable up to approximately 290 °C [³⁶]. The onset degradation temperature (Tonset, defined at 5% weight loss) increased from 291 °C for MDI-PU-1.0 to 316 °C for MDI-PU-1.5. These Tonset values (291–316 °C) fall within the range reported for castor-oil-based PUs: SAHA et al. [³⁷] observed T10% of 272–305 °C depending on composition, while ZULIANI et al. [³⁸] reported three-step degradation with soft-segment decomposition near 400–480 °C and slightly lower stability when PHB segments were present. This improvement in thermal stability is attributed to two factors: the higher density of thermally robust urethane linkages and the more extensive network of hydrogen bonds at higher hard segment contents, which requires greater thermal energy to disrupt [³⁹]. The degradation process occurred in two main stages, corresponding to the breakdown of the urethane hard segments followed by the decomposition of the castor oil soft segments at higher temperatures.

The mechanical performance of the MDI-PU series was evaluated through tensile and hardness testing, with representative stress-strain curves shown in Figure 4 and key data compiled in Table 2. The results reveal a classic trade-off between strength and flexibility, governed by the hard segment content [⁴⁰]. As the NCO/OH ratio increased from 1.0 to 1.5, the material transitioned from a soft, ductile elastomer to a rigid, high-strength plastic. Tensile strength increased dramatically from 5.5 MPa to 18.2 MPa [⁴¹], Young’s modulus rose from 15.3 MPa to 81.6 MPa [⁴²], and Shore D hardness increased from 25 to 48. This enhancement in stiffness and strength is due to the increased density of hard segments, which act as physical cross-links and reinforcing domains within the soft matrix. However, this rigidity came at the cost of flexibility, as the elongation at break plummeted from 352% for MDI-PU-1.0 to just 88% for MDI-PU-1.5 [⁴³]. For context, SAHA et al. [³⁷] reported tensile strengths of 10.8–15.3 MPa with 17–29% elongation for HMDI-crosslinked castor-oil/PHB-diol PUs at NCO/OH = 2.0–4.0; our CO-PU (MDI, NCO/OH = 1.2–1.5) attains comparable strength (11.5–18.2 MPa) but far greater extensibility (88–218%), consistent with the absence of crystalline PHB domains and higher soft-segment mobility.

Figure 4
Grouped stress-strain curves for MDI-PU series.

Table 2
Mechanical properties of MDI-PU series A as a function of NCO/OH ratio.

SAMPLE	NCO/OH RATIO	TENSILE STRENGTH (MPa)	YOUNG’S MODULUS (MPa)	ELONGATION AT BREAK (%)	SHORE D HARDNESS
MDI-PU-1.0	1.0	5.5 ± 0.4	15.3 ± 1.1	352 ± 25	25 ± 2
MDI-PU-1.2	1.2	11.5 ± 0.8	42.1 ± 2.5	218 ± 18	36 ± 2
MDI-PU-1.5	1.5	18.2 ± 1.1	81.6 ± 4.3	88 ± 10	48 ± 3

To visualize the structural origin of these mechanical differences, the surface morphology and phase separation were investigated using AFM. Figure 5 presents the AFM topography and phase images for the MDI-PU series. For the MDI-PU-1.0 sample, the phase image shows a relatively uniform morphology, indicating a high degree of phase mixing between the soft and hard segments. As the NCO/OH ratio increases to 1.2 and 1.5, a distinct nanophase-separated morphology becomes evident. The phase images for MDI-PU-1.5 clearly show discrete, brighter (stiffer) hard-segment-rich domains dispersed within a continuous, darker (softer) soft-segment matrix. The increased concentration and connectivity of these reinforcing hard domains directly explain the observed increase in modulus and tensile strength. This provides compelling visual evidence that the macroscopic mechanical properties are directly governed by the nanoscale phase separation, which is in turn controlled by the initial NCO/OH formulation. In addition to qualitative images, we now report AFM phase-contrast metrics (Δφ between hard- and soft-segment domains, and a two-peak histogram separation) and surface roughness (R_a) extracted from identical scan areas; larger Δφ with increasing [NCO]/[OH] indicates stronger nanophase contrast, aligning with literature that correlates phase-contrast growth with hard-segment association and modulus increase in PUs [³⁴, ⁴⁴].

Figure 5
Grouped AFM topography and phase images for MDI-PU-1.0, MDI-PU-1.2, and MDI-PU-1.5.

3.3. Influence of isocyanate structure (Series B: MDI vs. HMDI)

To understand the role of the hard segment’s chemical nature, the properties of the aromatic MDI-PU-1.2 were compared with those of the aliphatic HMDI-PU-1.2 at a constant NCO/OH ratio of 1.2. The results, summarized in Table 3, reveal that the isocyanate structure has a profound impact on the material’s performance and surface characteristics.

Table 3
Comparative properties of aromatic (MDI-PU-1.2) and aliphatic (HMDI-PU-1.2) polyurethanes.

PROPERTY	MDI-PU-1.2 (AROMATIC)	HMDI-PU-1.2 (ALIPHATIC)
Tg (°C)	−2.1	−25.4
Tonset (°C)	305	284
Tensile strength (MPa)	11.5 ± 0.8	7.0 ± 0.5
Elongation at break (%)	218 ± 18	455 ± 30
Water contact angle (°)	88 ± 2	75 ± 3
Water uptake (%, 72h)	1.5	3.1

The TGA curves and stress-strain curves demonstrate the significant differences between the two polymers [⁴⁵]. The MDI-based PU exhibited superior thermal stability (Tonset of 305 °C) [⁴⁶] and higher tensile strength (11.5 MPa) compared to the HMDI-based PU (Tonset of 284 °C, tensile strength of 7.0 MPa). This is attributed to the rigid, planar structure of the MDI’s aromatic rings, which promotes more efficient packing and stronger intermolecular interactions (including π-π stacking) within the hard domains, leading to a stiffer and more thermally stable network.17 In contrast, the cycloaliphatic structure of HMDI is more flexible and less sterically hindered, resulting in weaker hard-segment interactions [⁴⁷]. This leads to a much lower Tg (−25.4 °C) and a significantly more flexible material, as evidenced by its much higher elongation at break (455%).

The chemical nature of the isocyanate also directly influenced the surface properties of the polymers [⁴⁸]. As shown in Figure 6 and Table 3, the MDI-PU-1.2 film displayed a higher water contact angle of 110°, indicating a relatively hydrophobic surface [⁴⁹]. Conversely, the HMDI-PU-1.2 film had a lower contact angle of 82°, signifying a more hydrophilic character. This difference is a direct consequence of the molecular structure: the nonpolar aromatic rings of MDI contribute to a more water-repellent surface, whereas the aliphatic structure of HMDI results in a surface with higher polarity. This was further confirmed by the water uptake measurements, where the more hydrophilic HMDI-PU-1.2 absorbed more than twice the amount of water (3.1%) compared to the MDI-PU-1.2 (1.5%) over 72 hours [⁵⁰]. This difference in hydrophilicity is not merely a surface property; it has profound implications for the materials’ biodegradability [⁵¹]. The initial step of microbial degradation involves the adhesion of microorganisms and the action of extracellular enzymes on the polymer surface [⁵²]. A more hydrophilic surface is more readily wetted and colonized by microbes in an aqueous environment, and it allows for better access for hydrolytic enzymes. Therefore, it was hypothesized that the more hydrophilic HMDI-based polyurethane would exhibit a faster rate of biodegradation.

Figure 6
Water contact angle measurements for MDI-PU-1.2 and HMDI-PU-1.2.

3.4. Biodegradability and degradation mechanism

The end-of-life performance of the synthesized CO-PUs was assessed through soil burial and enzymatic degradation tests. The results, presented as weight loss over time in Figure 7 and summarized in Table 4, confirm that these bio-based materials are indeed biodegradable and that their degradation rate can be controlled by their chemical structure.

Figure 7
Weight loss curves of CO-PU films during the 180-day soil burial test.

Table 4
Percentage weight loss of CO-PU films after biodegradation tests.

SAMPLE	NCO/OH RATIO	ISOCYANATE TYPE	SOIL BURIAL WEIGHT LOSS (%, 180 DAYS)	ENZYMATIC DEGRADATION WEIGHT LOSS (%, 28 DAYS)
MDI-PU-1.0	1.0	Aromatic (MDI)	25.3 ± 2.1	14.8 ± 1.2
MDI-PU-1.2	1.2	Aromatic (MDI)	18.1 ± 1.5	9.5 ± 0.8
MDI-PU-1.5	1.5	Aromatic (MDI)	9.8 ± 0.9	4.2 ± 0.5
HMDI-PU-1.2	1.2	Aliphatic (HMDI)	35.5 ± 2.8	22.1 ± 1.9

The primary mechanism of degradation for these polyester-based PUs is the hydrolytic cleavage of the ester bonds within the castor oil soft segments by microbial enzymes (e.g., lipases, esterases) present in the soil [⁵³]. The data reveal two distinct trends. First, within the MDI-PU series, the rate of biodegradation decreased significantly as the NCO/OH ratio increased [⁵⁴]. After 180 days in soil, MDI-PU-1.0 lost over 25% of its initial weight, whereas MDI-PU-1.5 lost less than 10%.26 This is because a higher NCO/OH ratio leads to a higher cross-link density and a more rigid, compact polymer network. This dense structure physically hinders the diffusion of water and extracellular enzymes into the polymer matrix, thereby protecting the susceptible ester linkages and slowing the rate of degradation. Second, the structure of the isocyanate had a dramatic effect on biodegradability [⁵⁵]. The aliphatic HMDI-PU-1.2 exhibited the highest rate of degradation, with over 35% weight loss in the soil burial test and 22% in the enzymatic test. This was nearly double the degradation observed for its aromatic counterpart, MDI-PU-1.2 (18% and 9.5%, respectively). These 180-day values align with recent literature: ZULIANI et al. [³⁸] recorded up to ~25% mass loss in 150 days for a hydrophilic, bio-derived PDI-based CO-PU versus minimal change for a less hydrophilic PolyHDI analogue; they also observed decreased water contact angle after burial, supporting our hydrophilicity–degradability correlation. More broadly, reports on CO-based PU composites show enhanced fungal/soil degradation when polar or biodegradable co-segments are introduced, though often at the expense of tensile strength [¹⁴]. This result directly confirms the hypothesis derived from the surface property analysis. The greater hydrophilicity of the HMDI-based polymer facilitates more efficient surface colonization by microorganisms and provides better access for hydrolytic enzymes, leading to accelerated degradation [⁵⁶].

To visually support these findings, Figure 8 presents a schematic illustration of the degradation mechanism and the key structural factors influencing the biodegradation rate of CO-PUs. In the left panel, enzymatic hydrolysis of ester bonds by soil-residing lipases and esterases is depicted as the primary degradation pathway. The middle panel contrasts MDI-PU-1.2 and HMDI-PU-1.2, highlighting how the aliphatic HMDI-based polymer features a more hydrophilic and loosely crosslinked network, which facilitates microbial access and accelerates degradation. The right panel illustrates the inverse relationship between the NCO/OH ratio and soil burial degradation performance, wherein increased crosslinking density leads to reduced enzymatic and water penetration and consequently, slower degradation rates.

Figure 8
Schematic illustration of the degradation mechanism and structure-dependent biodegradation of CO-PUs.

The macroscopic weight loss observed after soil burial degradation was strongly supported by changes in the microstructure of the polyurethane films, as revealed by scanning electron microscopy (SEM). Figures 9 and 10 provide comparative SEM images of the four principal CO-PU samples—MDI-PU-1.0, MDI-PU-1.2, MDI-PU-1.5, and HMDI-PU-1.2—before and after 180 days of burial in soil. These images provide direct visual evidence of degradation phenomena and highlight the distinct stability profiles associated with variations in the polymer composition. In Figure 9A, the MDI-PU-1.0 sample initially exhibited a smooth, featureless surface. However, after 180 days of burial, severe degradation features emerged, including large erosion pits, significant surface cracking, and the presence of microbial colonies within these damaged zones. These observations align with the higher weight loss reported for this sample and indicate extensive microbial colonization and enzymatic hydrolysis at the surface. The presence of erosion pits suggests localized breakdown of the polymer matrix, possibly initiated at sites of lower crosslink density or phase-separated soft segments. The microbial colonies further confirm the role of biological agents in the deterioration process. In Figure 9B, MDI-PU-1.2 showed similar trends, albeit to a lesser extent. Cracks were still present, though smaller and less pervasive. The surface damage is evident, but microbial colonization is less apparent compared to MDI-PU-1.0, reflecting improved but still limited resistance to biodegradation.

Figure 9
(A) SEM images of MDI-PU-1.0 before and after soil burial. (B) SEM images of MDI-PU-1.2 before and after soil burial.

Figure 10A focuses on the MDI-PU-1.5 sample, which displayed only minor morphological changes after degradation. The “after” image shows a surface that is largely intact, with very slight roughening and no visible microbial features. This suggests that the higher NCO/OH ratio and increased hard segment content significantly enhanced the polymer’s resistance to microbial attack and hydrolysis. Conversely, Figure 10B shows the HMDI-PU-1.2 sample, which suffered extensive structural damage. The post-burial image reveals deep surface cracks and fungal hyphae penetrating the material, indicating advanced biodegradation driven by fungal invasion. The irregular surface and hyphal infiltration highlight the susceptibility of aliphatic-based PUs to microbial degradation, which is consistent with their more hydrophilic nature and lower crosslink density. Overall, the SEM evidence underscores the critical influence of both isocyanate type and NCO/OH ratio on the environmental durability of CO-PUs.

Figure 10
(A) SEM images of MDI-PU-1.5 before and after soil burial. (B) SEM images of HMDI-PU-1.2 before and after soil burial.

4. CONCLUSION

This research has successfully demonstrated the synthesis of a series of sustainable polyurethane biopolymers derived entirely from castor oil as the polyol source. Through a controlled two-step polymerization process, we have established clear and predictable structure-property-degradability relationships, providing a valuable framework for the design of eco-friendly materials. The study systematically revealed that the thermomechanical and biodegradation properties of these CO-PUs can be precisely tuned by adjusting key synthesis parameters. Increasing the [NCO]/[OH] molar ratio from 1.0 to 1.5 resulted in a significant enhancement of mechanical strength, modulus, hardness, and thermal stability. This improvement is directly linked to the increased hard segment content, which promotes greater microphase separation and a more robust network of physical cross-links via hydrogen bonding. However, this increased rigidity comes at the cost of reduced flexibility and, critically, a lower rate of biodegradation. Furthermore, the chemical nature of the diisocyanate was shown to be a powerful tool for controlling material properties. The use of an aromatic diisocyanate (MDI) produced a stiffer, stronger, and more thermally stable polymer, whereas an aliphatic diisocyanate (HMDI) yielded a more flexible and extensible material. Most importantly, the aliphatic HMDI-based polyurethane exhibited significantly enhanced hydrophilicity and, consequently, a much faster rate of degradation in both soil burial and enzymatic tests compared to its aromatic counterpart. This highlights a direct link between molecular structure, surface properties, and end-of-life performance. In conclusion, this work provides a comprehensive blueprint for developing castor oil-based polyurethanes with tailored performance profiles and controlled biodegradability. These materials represent a viable and sustainable alternative to conventional petroleum-based plastics. Future research should focus on exploring other novel bio-based diisocyanates and the incorporation of natural fillers or functional additives to further expand the property spectrum of these promising biopolymers, moving closer to a circular materials economy.

5. ACKNOWLEDGEMENTS

This work was supported by Key project of science and technology research program of Chongqing Education Commission of China (No. KJZD-K202403601).

6. BIBLIOGRAPHY

• ^[1] FINAYEVA, N., KRISTANTI, R.A., RACHANA, K., et al, “Biodegradation of microplastics: mechanisms, challenges, and future prospects for environmental remediation”, Tropical Aquatic and Soil Pollution, v. 5, n. 1, pp. 53–70, Jun. 2025. doi: http://doi.org/10.53623/tasp.v5i1.671.
  » https://doi.org/10.53623/tasp.v5i1.671
• ^[2] ARREDONDO-NAVARRO, A., DRONJAK, L., ROVIRA SOLANO, J., et al, “A review for prioritizing microplastic regulation and research: an integral approach”, Air, Soil and Water Research, v. 17, pp. 11786221241257367, Jan. 2024. doi: http://doi.org/10.1177/11786221241257367.
  » https://doi.org/10.1177/11786221241257367
• ^[3] ASIH, D.R., HANDAYANI, W., ANANDA, A.Z., et al, “An insight into potential phosphate bioremediation and renewable energy from agricultural waste via integrated wastewater treatment systems in Indonesia”, Environmental Research Communications, v. 6, n. 4, pp. 42001, Apr. 2024. doi: http://doi.org/10.1088/2515-7620/ad359c.
  » https://doi.org/10.1088/2515-7620/ad359c
• ^[4] SYNANI, K., ABELIOTIS, K., VELONIA, K., et al, “Environmental impact and sustainability of bioplastic production from food waste”, Sustainability, v. 16, n. 13, pp. 5529, Jun. 2024. doi: http://doi.org/10.3390/su16135529.
  » https://doi.org/10.3390/su16135529
• ^[5] SWETHA, T.A., BORA, A., ANANTHY, V., et al, “A review of bioplastics as an alternative to petrochemical plastics: Its types, structure, characteristics, degradation, standards, and feedstocks”, Polymers for Advanced Technologies, v. 35, n. 6, e6482, Jun. 2024. doi: http://doi.org/10.1002/pat.6482.
  » https://doi.org/10.1002/pat.6482
• ^[6] MIRI, Z., FARÈ, S., MA, Q., et al, “Updates on polyurethane and its multifunctional applications in biomedical engineering”, Progress in Biomedical Engineering, v. 5, n. 4, pp. 42001, Oct. 2023. doi: http://doi.org/10.1088/2516-1091/acef84.
  » https://doi.org/10.1088/2516-1091/acef84
• ^[7] ZHENG, X., CHEN, S., WANG, Y., “Analysis of mechanical properties of polyurethane concrete and its bond slip characteristics with rebar”, Matéria, v. 30, e20240712, 2025. doi: http://doi.org/10.1590/1517-7076-rmat-2024-0712.
  » https://doi.org/10.1590/1517-7076-rmat-2024-0712
• ^[8] PAN, Y., YIN, C., FERNANDEZ, C., et al, “A systematic review and bibliometric analysis of flame-retardant rigid polyurethane foam from 1963 to 2021”, Polymers, v. 14, n. 15, pp. 3011, Jan. 2022. doi: http://doi.org/10.3390/polym14153011. PubMed PMID: 35893975.
  » https://doi.org/10.3390/polym14153011
• ^[9] MA, Y., WANG, R., LI, Q., et al, “Castor oil as a platform for preparing bio-based chemicals and polymer materials”, Green Materials, v. 10, n. 3, pp. 99–109, Sep. 2022. doi: http://doi.org/10.1680/jgrma.20.00085.
  » https://doi.org/10.1680/jgrma.20.00085
• ^[10] LEE, J.H., KIM, S.H., “Fabrication of silane-grafted graphene oxide and its effect on the structural, thermal, mechanical, and hysteretic behavior of polyurethane”, Scientific Reports, v. 10, n. 1, pp. 19152, Nov. 2020. doi: http://doi.org/10.1038/s41598-020-76153-8. PubMed PMID: 33154454.
  » https://doi.org/10.1038/s41598-020-76153-8
• ^[11] OPREA, S., GRADINARIU, P., OPREA, V., “Properties and fungal biodegradation of the different cellulose derivatives structure included into castor oil-based polyurethane composites”, Journal of Composite Materials, v. 53, n. 25, pp. 3535–3548, Oct. 2019. doi: http://doi.org/10.1177/0021998319843334.
  » https://doi.org/10.1177/0021998319843334
• ^[12] LIAO, Y.-H., SU, Y.-L., CHEN, Y.-C., “The influence of neem oil and its glyceride on the structure and characterization of castor oil-based polyurethane foam”, Polymers, v. 13, n. 12, pp. 2020, Jun. 2021. doi: http://doi.org/10.3390/polym13122020. PubMed PMID: 34205593.
  » https://doi.org/10.3390/polym13122020
• ^[13] CHOI, K.K., PARK, S.H., OH, K.W., et al, “Effect of castor oil/polycaprolactone hybrid polyols on the properties of biopolyurethane”, Macromolecular Research, v. 23, n. 4, pp. 333–340, Apr. 2015. doi: http://doi.org/10.1007/s13233-015-3052-y.
  » https://doi.org/10.1007/s13233-015-3052-y
• ^[14] OPREA, S., GRADINARIU, P., OPREA, V., “Properties and fungal biodegradation of the different cellulose derivatives structure included into castor oil-based polyurethane composites”, Journal of Composite Materials, v. 53, n. 25, pp. 3535–3548, Oct. 2019. doi: http://doi.org/10.1177/0021998319843334.
  » https://doi.org/10.1177/0021998319843334
• ^[15] CARRERO, D.M., MORALES, J.M., GARCIA, A.C., et al, “Comparative analysis for three different immobilisation strategies in the hexavalent chromium biosorption process using Bacillus sphaericus S-layer”, Canadian Journal of Chemical Engineering, v. 89, n. 5, pp. 1281–1287, Oct. 2011. doi: http://doi.org/10.1002/cjce.20515.
  » https://doi.org/10.1002/cjce.20515
• ^[16] FIORI, S., MARIANI, A., RICCO, L., et al, “First synthesis of a polyurethane by frontal polymerization”, Macromolecules, v. 36, n. 8, pp. 2674–2679, Apr. 2003. doi: http://doi.org/10.1021/ma0211941.
  » https://doi.org/10.1021/ma0211941
• ^[17] DANE, T.G., BARTENSTEIN, J.E., SIRONI, B., et al, “Influence of solvent polarity on the structure of drop-cast electroactive tetra(aniline)-surfactant thin films”, Physical Chemistry Chemical Physics, v. 18, n. 35, pp. 24498–24505, 2016. doi: http://doi.org/10.1039/C6CP05221E. PubMed PMID: 27539382.
  » https://doi.org/10.1039/C6CP05221E
• ^[18] AL-SALEM, S.M., SULTAN, H.H., KARAM, H.J., et al, “Determination of biodegradation rate of commercial oxo-biodegradable polyethylene film products using ASTM D 5988”, Journal of Polymer Research, v. 26, n. 7, pp. 157, Jul. 2019. doi: http://doi.org/10.1007/s10965-019-1813-3.
  » https://doi.org/10.1007/s10965-019-1813-3
• ^[19] ROMANO, A., ROSATO, A., SISTI, L., et al, “Enzyme-catalyzed polyurethane adhesive degradation”, Reaction Chemistry & Engineering, v. 9, n. 12, pp. 3133–3145, 2024. doi: http://doi.org/10.1039/D4RE00253A.
  » https://doi.org/10.1039/D4RE00253A
• ^[20] CHOI, K.K., PARK, S.H., OH, K.W., et al, “Effect of castor oil/polycaprolactone hybrid polyols on the properties of biopolyurethane”, Macromolecular Research, v. 23, n. 4, pp. 333–340, Apr. 2015. doi: http://doi.org/10.1007/s13233-015-3052-y.
  » https://doi.org/10.1007/s13233-015-3052-y
• ^[21] KIM, M.-G., JO, K.-I., KIM, E., et al, “Preparation of polydimethylsiloxane-modified waterborne polyurethane coatings for marine applications”, Polymers, v. 13, n. 24, pp. 4283, Dec. 2021. doi: http://doi.org/10.3390/polym13244283. PubMed PMID: 34960833.
  » https://doi.org/10.3390/polym13244283
• ^[22] HASSAN, M.U., USMAN, M., BASHIR, R., et al, “Tribological analysis of molybdenum disulfide (mos2) additivated in the castor and mineral oil used in diesel engine”, Sustainability, v. 14, n. 17, pp. 10485, Aug. 2022. doi: http://doi.org/10.3390/su141710485.
  » https://doi.org/10.3390/su141710485
• ^[23] NGA, N.T.T., MINH, T.Q., THONG, P.Q., et al, “An experimental study on the influence of fine and coarse aggregates on the strength of polyurethane concrete for highway maintenance”, Matéria, v. 30, e20250269, 2025. doi: http://doi.org/10.1590/1517-7076-rmat-2025-0269.
  » https://doi.org/10.1590/1517-7076-rmat-2025-0269
• ^[24] ARISTRI, M.A., LUBIS, M.A.R., LAKSANA, R.P.B., et al, “Thermal and mechanical performance of ramie fibers modified with polyurethane resins derived from acacia mangium bark tannin”, Journal of Materials Research and Technology, v. 18, pp. 2413–2427, May. 2022. doi: http://doi.org/10.1016/j.jmrt.2022.03.131.
  » https://doi.org/10.1016/j.jmrt.2022.03.131
• ^[25] PAN, Y., FU, L., ZHOU, Q., et al, “Flammability, thermal stability and mechanical properties of polyvinyl alcohol nanocomposites reinforced with delaminated Ti3C2Tx (MXene)”, Polymer Composites, v. 41, n. 1, pp. 210–218, 2020. doi: http://doi.org/10.1002/pc.25361.
  » https://doi.org/10.1002/pc.25361
• ^[26] MASYKURI, M., NOFITASARI, H., RAHMAWATI, R.D., “Eco-friendly of sound-absorbing material based on polyurethane-urea with natural fiber waste”, Nano Hybrids and Composites, v. 41, pp. 9–19, Oct. 2023. doi: http://doi.org/10.4028/p-cpix3A.
  » https://doi.org/10.4028/p-cpix3A
• ^[27] KIM, J.-H., CHOI, S.H., PARK, M.G., et al, “Biodegradation of polyurethane by Japanese carpenter bee gut-associated symbionts Xanthomonas sp. HY-71, and its potential application on bioconversion”, Environmental Technology & Innovation, v. 28, pp. 102822, Nov. 2022. doi: http://doi.org/10.1016/j.eti.2022.102822.
  » https://doi.org/10.1016/j.eti.2022.102822
• ^[28] LI, X., YANG, F., LI, Y., et al, “Diselenide as a dual functional mechanophore capable of stress self-reporting and self-strengthening in polyurethane elastomers”, CCS Chemistry, v. 5, n. 4, pp. 925–933, Mar. 2023. doi: http://doi.org/10.31635/ccschem.022.202201874.
  » https://doi.org/10.31635/ccschem.022.202201874
• ^[29] YAMAMOTO, T., SHIBAYAMA, M., NOMURA, S., “Structure and properties of fatigued segmented poly (urethaneurea)s III. Quantitative analyses of hydrogen bond”, Polymer Journal, v. 21, n. 11, pp. 895–903, 1989. doi: http://doi.org/10.1295/polymj.21.895.
  » https://doi.org/10.1295/polymj.21.895
• ^[30] DULYANSKA, Y., CRUZ-LOPES, L., ESTEVES, B., et al, “FTIR monitoring of polyurethane foams derived from acid-liquefied and base-liquefied polyols”, Polymers, v. 16, n. 15, pp. 2214, Aug. 2024. doi: http://doi.org/10.3390/polym16152214. PubMed PMID: 39125240.
  » https://doi.org/10.3390/polym16152214
• ^[31] LI, Z., ZHOU, W., ZHANG, X., et al, “High-efficiency, flexibility and lead-free X-ray shielding multilayered polymer composites: layered structure design and shielding mechanism”, Scientific Reports, v. 11, n. 1, pp. 4384, Feb. 2021. doi: http://doi.org/10.1038/s41598-021-83031-4. PubMed PMID: 33623062.
  » https://doi.org/10.1038/s41598-021-83031-4
• ^[32] AKKOYUN, B.D., WIS, A.A., YILDIRIM, R., et al, “Enhanced crystallinity through melt annealing of thermoplastic polyurethanes”, Journal of Applied Polymer Science, v. 142, n. 11, e56593, Mar. 2025. doi: http://doi.org/10.1002/app.56593.
  » https://doi.org/10.1002/app.56593
• ^[33] TIAN, Y., LIU, Y., SU, Z., et al, “Biomimetic brushlike slippery coatings with mechanically robust, self-cleaning, and icephobic properties”, ACS Applied Materials & Interfaces, v. 12, n. 48, pp. 54041–54052, Dec. 2020. doi: http://doi.org/10.1021/acsami.0c14042. PubMed PMID: 33201670.
  » https://doi.org/10.1021/acsami.0c14042
• ^[34] CHENG, B.-X., GAO, W.-C., REN, X.-M., et al, “A review of microphase separation of polyurethane: characterization and applications”, Polymer Testing, v. 107, pp. 107489, Mar. 2022. doi: http://doi.org/10.1016/j.polymertesting.2022.107489.
  » https://doi.org/10.1016/j.polymertesting.2022.107489
• ^[35] KRISHNADAS, G., KARUPPASAMY, R., SELVAM, S., MANICKARAJ, K., “Evolving sandwich composites through structural modifications with polyurethane foam and glass fiber”, Matéria, v. 29, e20240507. 2024.
• ^[36] SILVA NETO, J.S., QUEIROZ, H.F.M., AGUIAR, R.A.A., et al, “A review on the thermal characterisation of natural and hybrid fiber composites”, Polymers, v. 13, n. 24, pp. 4425, Dec. 2021. doi: http://doi.org/10.3390/polym13244425. PubMed PMID: 34960977.
  » https://doi.org/10.3390/polym13244425
• ^[37] SAHA, P., KHOMLAEM, C., ALOUI, H., et al, “Biodegradable polyurethanes based on castor oil and poly (3-hydroxybutyrate)”, Polymers, v. 13, n. 9, pp. 1387, Apr. 2021. doi: http://doi.org/10.3390/polym13091387. PubMed PMID: 33923329.
  » https://doi.org/10.3390/polym13091387
• ^[38] ZULIANI, A., RAPISARDA, M., CHELAZZI, D., et al, “Synthesis, characterization, and soil burial degradation of biobased polyurethanes”, Polymers, v. 14, n. 22, pp. 4948, Nov. 2022. doi: http://doi.org/10.3390/polym14224948. PubMed PMID: 36433074.
  » https://doi.org/10.3390/polym14224948
• ^[39] DZULKIFLI, M.H., YAHYA, M.Y., MAJID, R.A., “Fire retardancy, thermal, and physico-mechanical properties of semi-rigid water-blown polyurethane foam from palm oil-based polyol”, Cellular Polymers, v. 41, n. 3, pp. 103–118, May. 2022. doi: http://doi.org/10.1177/02624893211061633.
  » https://doi.org/10.1177/02624893211061633
• ^[40] LI, S., LIN, X., GONG, S., “High strength, high stiffness and toughness, defect‐tolerant waterborne polyurethane with healing and antibacterial abilities”, Journal of Polymer Science, v. 62, n. 2, pp. 388–400, Jan. 2024. doi: http://doi.org/10.1002/pol.20230423.
  » https://doi.org/10.1002/pol.20230423
• ^[41] LUBIS, M.A.R., HANDIKA, S.O., SARI, R.K., et al, “Modification of ramie fiber via impregnation with low viscosity bio-polyurethane resins derived from lignin”, Polymers, v. 14, n. 11, pp. 2165, May. 2022. doi: http://doi.org/10.3390/polym14112165. PubMed PMID: 35683838.
  » https://doi.org/10.3390/polym14112165
• ^[42] LI, H., CHENG, H., ZHAO, F., “Thermoplastic polyureas with excellent mechanical properties synthesized from CO₂ ‐based oligourea”, Macromolecular Rapid Communications, v. 46, n. 15, pp. 2500139, 2025. doi: http://doi.org/10.1002/marc.202500139.
  » https://doi.org/10.1002/marc.202500139
• ^[43] KASPRZYK, P., GŁOWIŃSKA, E., PARCHETA-SZWINDOWSKA, P., et al, “Green TPUs from prepolymer mixtures designed by controlling the chemical structure of flexible segments”, International Journal of Molecular Sciences, v. 22, n. 14, pp. 7438, Jul. 2021. doi: http://doi.org/10.3390/ijms22147438. PubMed PMID: 34299058.
  » https://doi.org/10.3390/ijms22147438
• ^[44] SAKAMOTO, H., ASAKAWA, H., FUKUMA, T., et al, “Atomic force microscopy visualization of hard segment alignment in stretched polyurethane nanofibers prepared by electrospinning”, Science and Technology of Advanced Materials, v. 15, n. 1, pp. 015008, Feb. 2014. doi: http://doi.org/10.1088/1468-6996/15/1/015008. PubMed PMID: 27877650.
  » https://doi.org/10.1088/1468-6996/15/1/015008
• ^[45] SUN, L., HUANG, H., GUAN, Q., et al, “Cooperative chemical coupling and physical lubrication effects construct highly dynamic ionic covalent adaptable network for high-performance wearable electronics”, CCS Chemistry, v. 5, n. 5, pp. 1096–1107, May. 2023. doi: http://doi.org/10.31635/ccschem.022.202202037.
  » https://doi.org/10.31635/ccschem.022.202202037
• ^[46] OH, J., KIM, Y.K., HWANG, S.-H., et al, “Synthesis of thermoplastic polyurethanes containing bio-based polyester polyol and their fiber property”, Polymers, v. 14, n. 10, pp. 2033, May. 2022. doi: http://doi.org/10.3390/polym14102033. PubMed PMID: 35631915.
  » https://doi.org/10.3390/polym14102033
• ^[47] OPREA, S., POTOLINCA, V.O., “Synthesis and properties of water‐dispersible polyurethanes based on various diisocyanates and PEG as the hard segment”, Journal of Applied Polymer Science, v. 140, n. 24, e53948, Jun. 2023. doi: http://doi.org/10.1002/app.53948.
  » https://doi.org/10.1002/app.53948
• ^[48] ZHANG, S., ANDRE, J.S., HSU, L., et al, “Nondestructive in situ detection of chemical reactions at the buried interface between polyurethane and isocyanate-based primer”, Macromolecules, v. 53, n. 22, pp. 10189–10197, Nov. 2020. doi: http://doi.org/10.1021/acs.macromol.0c01862.
  » https://doi.org/10.1021/acs.macromol.0c01862
• ^[49] ZONG, H., ZHAO, X., WU, C., et al, “Synthesis and characterization of castor oil-based polyols with fluorine-containing pendant groups”, Journal of Adhesion Science and Technology, v. 38, n. 5, pp. 795–814, Mar. 2024. doi: http://doi.org/10.1080/01694243.2023.2243677.
  » https://doi.org/10.1080/01694243.2023.2243677
• ^[50] BRATASYUK, N.A., OSTANIN, S.A., MOKEEV, M.V., et al, “Water transport in epoxy/polyurethane interpenetrating networks”, Polymers for Advanced Technologies, v. 33, n. 10, pp. 3173–3191, Oct. 2022. doi: http://doi.org/10.1002/pat.5769.
  » https://doi.org/10.1002/pat.5769
• ^[51] KAMACI, M., KAYA, İ., “Fabrication of biodegradable hydrogels based on chitosan and poly(azomethine‐urethane) containing phenyl triazine for drug delivery”, Polymers for Advanced Technologies, v. 33, n. 9, pp. 2645–2655, Sep. 2022. doi: http://doi.org/10.1002/pat.5720.
  » https://doi.org/10.1002/pat.5720
• ^[52] SCHNEIER, A., MELAUGH, G., SADLER, J.C., “Engineered plastic-associated bacteria for biodegradation and bioremediation”, Biotechnology for the Environment, v. 1, n. 1, pp. 7, Jul. 2024. doi: http://doi.org/10.1186/s44314-024-00007-0. PubMed PMID: 39026535.
  » https://doi.org/10.1186/s44314-024-00007-0
• ^[53] ZHU, B., WANG, D., WEI, N., “Enzyme discovery and engineering for sustainable plastic recycling”, Trends in Biotechnology, v. 40, n. 1, pp. 22–37, Jan. 2022. doi: http://doi.org/10.1016/j.tibtech.2021.02.008. PubMed PMID: 33676748.
  » https://doi.org/10.1016/j.tibtech.2021.02.008
• ^[54] HILMI, N.H.A., LODIN, V., JESUET, M.S.G., et al, “Biodegradability properties of polyurethane film made from Eucalyptus pellita wood polyol.”, Borneo International Journal of Biotechnology, v. 3, pp. 147–158, 2023.
• ^[55] SERRANO, L., RINCÓN, E., GARCÍA, A., et al, “Bio-degradable polyurethane foams produced by liquefied polyol from wheat straw biomass”, Polymers, v. 12, n. 11, pp. 2646, Nov. 2020. doi: http://doi.org/10.3390/polym12112646. PubMed PMID: 33182792.
  » https://doi.org/10.3390/polym12112646
• ^[56] SUN, Y., WU, M., ZANG, J., et al, “Plastisphere microbiome: methodology, diversity, and functionality”, Imeta, v. 2, n. 2, e101, May. 2023. doi: http://doi.org/10.1002/imt2.101. PubMed PMID: 38868423.
  » https://doi.org/10.1002/imt2.101

Publication Dates

• Publication in this collection
  31 Oct 2025
• Date of issue
  2025

History

• Received
  03 July 2025
• Accepted
  12 Sept 2025