Isolation and characterization of novel bioplasticizers from rose (Rosa damascena Mill.) petals and its suitability investigation for poly (butylene adipate-co-terephthalate) biofilm applications

Abstract

The current growing environmental awareness has forced the use of biodegradable plasticizers, which are sustainable and abundant in plant resources. Rose petal plasticizers (RPP) act as an actual substitute for chemical plasticizers in this situation as they are biocompatible and biodegradable. Chemical procedures like amination, alkalization, and surface catalysis are used to extract the natural emollients from rose petals. XRD, FT-IR, and UV studies were used to understand the characteristics of the rose petal plasticizer. Based on the XRD data, the RPP's crystallinity size (CS) and crystallinity index (CI) values were determined to be 9.36 nm and 23.87%, respectively. The surface morphology of the isolated plasticizer is investigated using SEM, EDAX analysis and AFM. RPP surface pores with rough surfaces are visible in SEM images, which make them appropriate for plasticizing novel bioplastics with superior mechanical qualities. The plasticizer's heat degradation behaviour is investigated using thermogravimetric and differential thermogram analysis curves. Following the characterization of the synthesised molecules, the plasticization effect was examined using a biodegradable polymer matrix called poly (butylene adipate-co-terephthalate) (PBAT). The reinforcement interface was also examined using scanning electron microscopy analysis. RPP-reinforced films demonstrated greater flexibility and superior surface compatibility at a 5% loading compared to PBAT-only films. Based on a number of reported features, RPP could be a great plasticizer to address future environmental problems.

Introduction

Ecological issues have grown exacerbated as the state of our planet's natural resources has declined. To attain sustainability, these issues have compelled consumers and companies to adopt environmental economics. Governments and economists are becoming more interested in environmental economics, but the Sustainable Development Goals (SDGs) have also recently gained global attention (Setioningtyas et al. 2022).

In South Asia, around eight million metric tonnes of flowers are thrown into the rivers every year for religious purposes. Every day, people across the nation bring more than 800 million metric tonnes of flowers to temples to offer them to the god, wish for a good life, and celebrate. According to the TATA Energy Research Institute (TERI), waste production will increase by 260 million tonnes by 2047, creating unmanageable waste disposal challenges for urban centres. Flowers left in open landfills after being improperly disposed of could bring about a number of health risks. After a few days of storage, microorganisms begin to break down the waste from flowers, producing dangerous gases in the process (Ferronato and Torretta 2019). Methane (CH₄), carbon dioxide (CO₂) and ammonia (NH₃) are some of the gases that cause the foul odour and are also a major contributor to greenhouse gas emissions. Floral waste contains significant amounts of lignocellulose, cellulose, crude proteins, crude fibres, essential oils and other nitrogenous substances. Such components of floral waste can be used as a source of bioenergy (Khan et al. 2021).

The rose (Rosa damascena Mill.) belongs to the rose family (Rosaceae) and is known as the "king of flowers"." It is a woody and prickly shrub. It is portrayed as a symbol of love and beauty in both peace and conflict. It is a shrub plant with over 2000 cultivars and hundreds of species. While some species are native to Africa, North America and Europe, a large proportion of species originate from Asia. The plant can reach a height of up to 6 m (Leghari et al. 2016). In the Middle Ages, roses were used in a variety of medicinal preparations (Wang 2024), including rose syrup (tonic, anti-infectious), moist jam (astringent), rose honey (antiseptic, mouthwash), rose decoction (analgesic) and rose oil (antipyretic, antiseptic). Rose water was used internally to relieve weakness and nervousness, and it was also used as an anti-inflammatory eyewash.

The aim of modern research and development is to find suitable biodegradable, economically viable and environmentally friendly green materials that can replace harmful, non-disposable synthetic materials (Campano et al. 2022). Nowadays, there is a great interest in biopolymer-based composites as they are widely accepted in a variety of industries without compromising environmental requirements (Abbasi et al. 2023). While they reduce the hardness, softening temperature and embrittlement of polymers, plasticizers are generally used to increase their elasticity and stretchability. To obtain natural, biodegradable plasticizers, agricultural products and waste can be used, which are economical, environmentally friendly and available in large quantities. Agricultural products such as trees, oil plants, cereals, vegetables, flowers and fruits and their waste are the source of a number of natural plasticizers (Saini et al. 2015).

Generally, a plasticizer is described by the IUPAC council as "a substance or a material incorporated into a plastic to increase its flexibility, workability, or distensibility." Plasticizers main function is to make polymers more flexible and processable by lowering the glass transition temperature (Tg). It is widely accepted that a plasticizer's low molecular weight enables it to occupy intermolecular gaps, lowering the hydrogen bonding and weak van der Waals forces among the polymer groups. The 3D molecular organization of polymers is altered by plasticizers, which lowers the energy needed for molecular motion (Yin et al. 2022). The lubricity theory states that the plasticizer penetrates the matrix, settles inside the polymer chains, and reduces intermolecular frictions. The macromolecules slide over each other when a piece of plastic bends. To prevent the hard matrix from reforming, the plasticizer lubricates the movement of the molecules by reducing their internal sliding resistance. The amount of free volume in a rigid polymer is extremely small. By increasing the free space and giving the polymer a rubbery, pliable texture, plasticizers accelerate the movement of the polymer molecules (Daniels 2009).

Researchers are increasingly focusing on bio-based plasticizers made from vegetable oils, citrates and glucose derivatives, which are able to soften both fossil and bio-polymers. As an alternative to other organic plasticizers, there is a growing interest in plasticizers that cause less agitation and are less hazardous (Narayana Perumal et al. 2023). The key objective is to develop environmentally friendly macro- and molecular plasticizers that have the best plasticizer efficiency. In continuation of our interest (Sunesh et al. 2022) (Edayadulla et al. 2023), we have extracted the bioplasticizers from the waste of Rosa damascena flower petals. The physico-chemical parameters, thermal features, and surface morphology of the bioplasticizers were examined and contrasted with those of other recognised natural plasticizers. With a polybutylene adipate terephthalate (PBAT) matrix for the production of biofilm for cutting-edge applications, the plasticizing impact of these innovative bioplasticizers was examined.

Materials and methods

Agro solid waste as a source for bioplasticizers:

The identification of a promising plant material for the separation of bio-plasticizers was the initial stage of the current investigation. As a result, it is reasonable to assume that discarded rose petals are an excellent resource for these macromolecular substances. The waste flower petals were collected from the Madurai flower market and near the famous ancient Meenakshi temple, in Madurai—South India.

Extraction of bio-plasticizers

The rose petals were first separated from the waste flowers. The collected petals were washed with Milli-Q water and shade-dried.

Phytoremediation

Approximately 0.5 kg of dried petals were treated with 1 L of ammonia and soaked for 3 h to remove traces of water, minerals and unwanted toxic content that may have clung to the surface of the raw material.

Slow pyrolysis

After phytoremediation, the isolated materials were taken separately and subjected to slow pyrolysis. About 50 g of potassium chloride and 0.5 L of hydrochloric acid were added and immersed for 4 h. The process of pyrolysis enabled the sample to be transformed into a semi-solid condition with a high carbon content and less liquid. The delignification process can take place and the biomass can be separated with the aid of an acid catalyst.

Alkylation process

The resulting solid residue was then subjected to an alkylation procedure using a 50% NaOH solution. During this process, the plasticizers floating on the surface of the supernatant were separated and purified by sodium hypochlorite mediated bleaching. The biomaterials from the recovered rose petals were then shade dried for 8 h to eliminate moisture. Finally, the separated plasticizers were reduced in size using the ball milling technique. Figure 1 illustrates the techniques used to extract plasticizers from rose petals.

Fig. 1.

Schematic representation for the extraction of plasticizers from Rose petals

Characterization of bio-plasticizers

To determine the unique characteristics of the bioplasticizer; the physico-chemical, thermal, and surface properties of the isolated bioplasticizers were examined in accordance with standard profile. To reveal the material's suitability as a bio-plasticizer for lightweight applications, physical investigation of the material is necessary to ascertain its particular density. The chemical analysis helped to determine the main chemical components, functional groups, and crystallinity nature of the substance. Thermal tests and surface morphological analysis were conducted to ascertain the surface characteristics and temperature endurance of the biopolymers extracted, hence determining their suitability for composite or biofilm development (Liu et al. 2020).

FT-IR analysis

For the purpose of identifying the various functional groups contained in the RPP, IR spectra were captured in KBr using a Jasco 4600 Fourier transform infrared spectrophotometer. The experiment was carried out in non-contact mode with a 4 cm⁻¹ resolution. Then, at room temperature, the FT-IR spectra were captured in the 4000–500 cm⁻¹ wavelength region. To confirm the suspicious material's chemical composition and plasticizing properties, the resulting spectrogram was also utilized to explain the chemical groups and related chemical components that were present in it.

Ultraviolet (UV) visible spectroscopy analysis

With the help of a Shimadzu UV-2101 PC spectrometer with an integrating sphere where the material was loaded, the UV visible spectroscopic examination of the isolated biopolymers was carried out. The visible spectrum that resulted was measured in the 200–700 nm wavelength range. The distinctive peaks seen in the spectra are used to confirm the presence of substances with plasticizing properties (Battegazzore et al. 2014).

Density analysis

Using an AccuPyc II 1340 model pycnometer and helium gas flow, the density of plasticizers isolated from rose petals was examined (Reshmy et al. 2021). The sample was dried at 105°F for 24 h before being exposed to remove any moisture. To ensure that all traces of water were removed, the samples were then maintained in a desiccator. Following the collection of five different measurements, the average density was estimated using the relation (1) while the density study was being done at a temperature of 27 °C.

$$\text{Density}=\text{mass}\left(\text{in grams}\right)/\text{volume}\left({\text{in , cm}}^3\right).$$ 1

X-ray diffraction analysis

The XRD technique was used to calculate the percentage of crystalline and amorphous fractions in the RPP. Equipment from the Bruker XRD line was used for this experiment. The extracted RPP was positioned inside the sample-holder, which was then put under an X-ray. Then, a moving X-ray detector from 2θ = 0°–100° was used to locate the diffracted X-ray. The detector moved in steps of 80 s each and at a speed of 0.020°. The wavelength of the X-ray produced by the X-ray generator was 1.54060 Å. The X-ray generator's current and voltage were set at 10.0 mA and 30.0 kV, respectively. The system was kept at its optimal temperature of 25 °C. Applying Eqs. (2) and (3), the Origin Pro 2021 software (Senthamaraikannan and Kathiresan 2018) was used to determine the crystallinity index (CI) and crystallite size (CS) of the biopolymers. A_crystalline represents the crystalline curve proportion in relation (2), whereas A_amorphous designates the amorphous curve fraction. The relationship (3) is Scherrer's formula, where K stands for the Scherrer's constant (0.89), specific wavelength is represented by λ, β is the Bragg's angle (CUKα = 1.5406 Å) which indicates the full-width at half-maximum wavelength of a line change and D is the crystallinity size (nm).

$$\text{CI}\left(\%\right)=\frac{A_{\text{crystalline}}}{A_{\text{crystalline}}+A_{\text{amorphous}}}\times 100$$ 2

$$D=\frac{k\lambda }{\beta \cos \theta }$$ 3

Thermal analysis

Thermogravimetric analysis

The extracted RPP underwent a thermogravimetric analysis (TGA) using a TG/DTA Exstar 6300 device. The thermal and dehydration characteristics of RPP are crucial for the development of bioplasticizers meant for high-temperature and high-performance applications (Vinod et al. 2021). The RPP can be used as a binding agent in polymers as well. Here, TGA was used to investigate the RPP's thermal stability and degradation characteristics. In a nitrogen environment, this analysis was done. The RPP sample was weighed (4.5 mg) before being placed into a room-temperature alumina furnace. The temperature of the sample increased from 30 to 900 °C at a steady rate of 20 °C per minute. The RPP sample lost weight for every 1 °C rise in temperature, and TGA plots showed the proportion of weight loss against temperature. Differential thermographic (DTG) analysis was performed on the RPP sample to use the peaks produced to determine the breakdown of the samples at certain temperatures. The TGA and DTG plots were used to forecast the suggested plasticizer's maximum degradation temperature limit.

Activation energy analysis

The Coats-Redfern equation, which is as follows, was used to conduct the kinetic analysis of the RPP (Indran et al. 2022).

$$\text{ln}\left[\frac{g\left(x\right)}{T^2}\right]=ln\left[\frac{\mathit{AR}}{\beta E},\left(1,-,\frac{2RT}{E}\right)\right]-\frac{E}{R}\frac{1}{T}$$ 4

where t stands for duration (min) and β denotes for linear heating rate, T indicates absolute temperature in Kelvin scale, R represents universal gas constant (8.314 J mol⁻¹ K⁻¹), g(x) represents the integral form of the reaction dt/dx mechanism model.

Surface property analysis

It is essential to reveal the morphological properties of bio-plasticizers in terms of their surface fineness, components distribution, and surface parameters to prove the acceptability of the extracted material for composite or biofilm applications. The surface features of the bio-plasticizers were investigated using atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), and SEM–EDX techniques (Vijay et al. 2021).

SEM/ SEM–EDX analysis

The Σ version of Carl Zeiss, Germany, 5.07 Beta-Field Emission Scanning Electron Microscope (FESEM) is used to analyze the surface morphology of the extracted RPP sample. In this experiment, the working distance was set to around 12.2 mm, and the accelerating voltage was set to 15 kV. The photographs intensity was tuned to distinguish particles from the background. In all, 100×, 500× and 5.00 k× were used to magnify the photos in two separate shots. The particle size investigation used the ImageJ image processing program from the National Institutes of Health. 28 particles were looked at to determine the mean length (m) and shape descriptors (Grishkewich et al. 2017).

Energy dispersive X-ray spectroscopy

Energy dispersive X-ray spectroscopy (EDX) may be used to quantitatively count the elements (such as carbon, nitrogen, oxygen, magnesium, sodium, etc.) present on the extracted RPP. The distributions of elements for treated materials were measured five times with the help of an INCAPenta FETx3 model EDX analyzer linked to a TESCON VEGA (third generation) Scanning Electron Microscope. The average value was then recorded.

Atomic force microscopic (AFM) analysis

The Flex AFM 5 instrument was used to acquire the data from the RPP sample's surface. A scan head with a resolution of 0.1 nm is part of the apparatus. The data are transmitted back into a system, which creates topographical features. With the help of a nanoscale AFM, we measured roughness parameters like the total height of the roughness profile (R_t), the average roughness of the surface (R_a), the distance between the surface's tallest 'peak' and its deepest 'valley' (R_z), and the root mean square deviation value of the profile's departures from the mean line (R_q or R_rms). The ratio between the mean of the fourth power of the height values and the fourth power of R_q within the sample length (R_ku) was used to determine the sharpness of the surface height distribution. A surface that is spiky will have a high kurtosis value, whereas a surface that is bumpy would have a low kurtosis value. The average of the surface's first derivative, or the surface's deviation from symmetry, is referred to as skewness (R_sk).

Plasticizer effect analysis with PBAT

The investigation of the plasticizing effect of RPP reinforcement was made possible by the creation of a polybutylene adipate-co-terephthalate (PBAT) film. Tensile strength, elongation modulus and elongation break percentage of the biofilm's mechanical characteristics were assessed using a universal testing apparatus (QRS-S11H, Quro) at room temperature and 40% relative humidity. To verify RPP's plasticizing impact on PBAT matrix-based biofilm, a flexibility research involving unaided observation and SEM morphological analysis was conducted using a Thermo Scientific™ Axia™ ChemiSEM™ Scanning Electron Microscope., which operates at 5–10 keV and was manufactured by Thermo Fisher Scientific, Waltham, MA USA (gold coating, Edwards Sputter Coater, UK).

Results and discussion

Fourier transform infrared (FT-IR) spectroscopy

The FT-IR spectra of the newly isolated plasticizer RPP are shown in Fig. 2. Remarkable peaks identified are 3451 cm⁻¹, 1639 cm⁻¹, 1553 cm⁻¹, 1455 cm⁻¹, 1392 cm⁻¹, 1190 cm⁻¹, 842 cm⁻¹ and 649 cm⁻¹. Usually, the O–H or N–H stretching modes of proteins, carbohydrates, flavonoids, and adsorbed water are typically responsible for the strong broad bands in the 3700 to 3000 cm⁻¹ region. The broad peak at 3451 cm⁻¹ is due to the dimeric OH stretching frequency. Evidence for the existence of flavonoid compounds in the biomass is provided by the stretching bands of the carbonyl groups (C=O) and C=C, which are the cause of vibration in the range of 1639 cm⁻¹ and 1553 cm⁻¹, respectively (Hssaini et al. 2022). Sharp stretching vibration at 1639.81 cm⁻¹ confirms the presence of the following groups in the material: alkenes, organic nitriles, conjugated ketone, open-chain imino/azo group. The absence of a signal at 1739 cm⁻¹ further demonstrated that the ester carbonyl vibrations from the acetyl, feruloyl, and p-coumaryl groups of the lignin constituents have been removed during the delignification process (Nanthakumar et al. 2018). The peak at 1553 cm⁻¹ is due to the presence of secondary amine or N–O stretching of nitro compounds. Another sharp peak observed at 1455 cm⁻¹ is due to the presence of polymeric (-CH₂-) methylene group. C–C vibrations and methyl interactions are responsible for the peak at 1190 cm⁻¹. The minor peaks after 1400 (the fingerprint area) are caused by solvents, hydrohalogens at 842 cm⁻¹, or any other silicates found in the plasticizer. With the addition of NaOH, the structure underwent polymeric condensation and comprises a macromolecule with a high molecular weight. This includes both the polyphenol structure and the (CH₂)n head with the same polyphenlols.

Fig. 2.

FT-IR spectra of plasticizers isolated from Rose petals

UV–visible absorption spectra of RPP

The resulting spectra are shown in Fig. 3, which shows the bioplasticizer sample's UV–visible absorbance in the 200–700 nm wavelength range. Bioactive substances including flavonoids and other polyphenolic compounds are present in the absorbance range of 200–400 nm. Flavonoids often exist as glycosylated monomers or flavan-3-ol oligomers (proanthocyanidins = condensed tannins) in a variety of environments (Thilakarathna and Vasantha Rupasinghe 2013). In their UV spectra, most flavonoids show two substantial absorption maxima: band II, which is in the 200–285 nm range, and band I, which is in the 300–400 nm area (Mabry et al. 1970).

Fig. 3.

UV–Visible spectra of the newly isolated plasticizer from Rose petals

The absorbance at 227.4 nm and the other peaks in the range of 310 to 400 nm, which correspond to band I of flavonoids, may be attributed to band II of flavonoids in the UV spectrum of RPP biomass. The peak absorption in the region 256.2 nm is caused by the polyphenolic bioactive compounds and may possibly be influenced by the presence of polyphenolic acid (Sisa et al. 2010). The absorbance in the vicinity of 280.6 nm is related to saponins. The phenolic components like flavonoids and tannins are present in the L. sativum extract based on the absorbance in the 230–290 nm wavelength range (Malar et al. 2018). Different types of flavonoids distinctive UV absorption bands I and II have been observed elsewhere (Table 1). The fact that RPP contains the chemical fractions phenols, alkenes, alkyl halides, amines, aromatics, nitro-compounds, and alcohols, which are the major chemical fractions of phenolic derivatives that the plant synthesises as a defence mechanism, further supports the conclusion that RPP is a derivative of phenolic compounds.

Table 1.

UV absorption ranges for flavonoid compounds present in plant sources

Band II (nm)	Band I (nm)	Flavonoid class
220–280	300–355	Flavone
210–280	320–350	Flavonols (3-OH substituted)
205–280	340–380	Flavonols (3-OH free)
245–275	310–335 shoulder	Isoflavone
–	320 peak	Isoflavones
275–295	300–330 shoulder	Flavonones and dihydroflavonols
220–275	340–390	Chalcones
220–275	380–430	Aurones
265–285	465–560	Anthocyanidins and anthocyanins

X-ray diffraction analysis

The crystallinity of the bioplasticizers was assessed using XRD (Fig. 4). X-ray diffraction offers details on crystal textures, optimum orientations for crystals, and other structural factors like average grain size, crystallinity, strain, and crystal defects. The diffraction patterns were measured, noted, and plotted in relation to the scans of the diffraction angle (2θ) from 10° to 100°. Six RPP-specific diffraction peaks can be found in the XRD patterns at 2θ = 15.83°, 32.27°, 34.21°, 42.03°, 52.88°, and 67.12°. The Fig. 4 displayed three significant peaks in the crystallographic plane at 2θ = 15.83°, 32.27°, and 34.21° as well as three slender broad peaks in the amorphous plane at 2θ = 42.03°, 52.88°, and 67.12°.

Fig. 4.

X-ray diffractogram of plasticizers isolated from Rose petals

The amorphous part of the plasticizer leads to more disorganised structure. The abnormality causes a more flexible backbone, which consequently improves the mobility of charge carriers (Naiwi et al. 2018). On the basis of XRD curves, we have evaluated the crystallinity of the plasticizers. The RPP has crystallites that are 9.36 nm in size and a crystallinity index of 23.87%. To support the plasticizer's amorphous nature, the percentage of crystallinity has been computed.

The peak's extension suggests that the nature of the RPP is amorphous. The increased amorphous structure suggests that the bioplastizier is highly hydrated. The amorphous condition of the plasticizer was probably produced by RPP's greater molecular weight, which has a lower capacity for crystallisation. Its size may have also impeded the rearrangement (Domene-López et al. 2019). Another explanation for this can be because there are little or no hydrogen bond interactions between RPP molecules and the low crystallinity index of 23.87% (Singh et al. 2020). Additionally, the low crystallinity index and crystalline size are required to offer the plasticizing action that increases the material's flexibility, compatibility, and typically allows simple inclusion into polymer matrix possible. The following Table 2 can be used to compare the CI and CS values of various plant materials.

Table 2.

Crystalline index and crystalline size of RPP biomaterials in comparison to those of other sources

Bio material	CI (%)	CS (nm)	References
Ficus religiosa	42.92	5.18	Moshi et al. (2020)
Sida rhombifolia	56.6	2.75	Gopinath et al. (2015)
Flax	70	2.8	Moryganov et al. (2018)
Ferula communis	48	1.6	Seki et al. (2013)
Juncus effusus	33.4	3.6	Xia et al. (2020)
Epipremnum aureum	49.33	15	Maheshwaran et al. (2017)
Perotis indica	48.3	15	Prithiviraj et al. (2016)
Tridax procumbens	34.46	25.04	Ayyanar et al. (2022)
Ramie	58	16	Qu et al. (2020)
Furcraea foetida	52.6	28.36	Manimaran et al. (2018)
RPP	23.87	9.36	This work

Thermal analysis

Thermal stability of RPP

Thermogravimetric Analysis (TGA) was used to monitor temperature to evaluate the thermal property of the bioplasticizer. It was found that when the temperature increased, the weight of the bioplasticizer dropped. Inherent properties of the macromolecules as well as molecular interactions between the various molecules determine a polymeric material's heat stability. When the supplied thermal energy is greater than the bond dissociation energy of the individual chemical bonds, the macromolecules' chains or bonds going to break (Ray et al. 2009). Figure 5 displays the outcomes from the TG and DTG of RPP. The breakdown process in RPP is a three-step mechanism. The outcome demonstrated the great relative thermal strength of bioplasticizer. Between 30 and 100 °C, the first weight loss can be obtained by the adsorbed moisture evaporating at a rate of about 11.5%. The very light volatile matter chemicals are lost at this point, and the water evaporation-induced thermal breakdown process takes place (Amin et al. 2019). The mass did not decrease between 100 and 200 °C, as seen in Fig. 5. Between 200 and 400 °C, the second step of RPP's thermal degradation took place. The random breaking of the cellulose's glycosidic bond and the depolymerization of hemicellulose both occur at this stage (Poletto et al. 2014). Levoglucosan is formed when the hydroxyl group on the glucose ring is dehydrated. This is followed by the formation of the aldehyde group when the glucose ring is cleaved. As the temperature raises, aromatic rings such as benzene substituted and furans with –CH₂ or –CH₂-O-CH₂ as the primary chain are formed (Zaidar et al. 2021).

Fig. 5.

TGA/DTG curves of plasticizers isolated from Rose petals

Due to the breakage of the cellulose chain, the degradation of all biocomposites took place between 272 and 282 °C (Shen et al. 2013). Because a significant amount of material (45%) was lost, this second stage is the primary thermal decomposition stage. Stage 3 is the phase that follows the release of volatile material from the samples at temperatures between 400 and 900 °C. At 500 °C, lignin starts to degrade. It is extensively cross-linked and has three distinct kinds of benzene-propane units with a very high molecular weight. As a result, lignin is difficult to break down and has very high heat stability. The bioplasticizer's fixed carbon content was a meagre 19%. The charcoal is now flammable because of the volatile substance that surrounds it and the oxygen that has spread onto its surface, burning both the charcoal and the volatile materials at the same time. This step happens when volatile materials that either emit or create carbon are released (Wahyuningtiyas et al. 2017). The process of carbonising the sample, which begins at a temperature over 500 °C, was confirmed at this stage by a increase in the strength of the aromatic carbon resonance while a decline in the intensity of the aliphatic carbon resonance. Inorganic materials were produced by the pyrolysis of carbonated compounds over 500 °C and were found in the residual residue samples (Tan et al. 2022). The subsequent heat flow addressed the destruction of the stable constituents, such as tannins, saponins, and other non-ferrous components. This was the final step of degradation. 18% of the original residue was left behind. The weight loss at higher temperatures, as indicated by the TGA in Fig. 5, further supports the presence of a larger molecular weight crosslinked fraction in the reaction product (Stolp and Kodali 2019). Maximum deterioration, as indicated by the DTG curve, happened at 343 °C. The TGA pattern is unquestionably supported by the DTG curve. The degradation above this temperature, which can be explained by the oxidation and breakdown of the char to low molecular weight gaseous compounds, degradation of RPP at 343 °C was caused by depolymerization, dehydration, and decomposition of hydroxyl units followed by the production of char (Rahman et al. 2014). Thermal experiments of the same kind were also disclosed for various biopolymers, including epoxidized soybean oil (ESO) and epoxidized cardanol-myristate (ECD-MA) act as plasticizers in PVC/30ESO/5ECD-MA (314.4 °C) (Yang et al. 2023), T_max is displayed in films using arrowroot starch (AS) and glycerol (G) as plasticizer at 321.53 °C (Tarique et al. 2021), Triester-amide, a novel primary plasticizer for poly(vinyl chloride) displays, is based on thiophene and ricinoleic acid and decomposes between 311.83 and 413.83 °C (Mhaske and Argade 2006), the plasticizer and all other low-molecular components are broken down at 350 °C when bio-based plasticizers (epoxidized esters of glycerol derived from soybean and canola oil) are studied with natural rubber and thermal breakdown of flame-retardant bio-based co-plasticizer for PVC synthetic materials occurs at 300.2 °C (Xu et al. 2020).

Kinetic analysis

The Coats-Redfern method was used to calculate the kinetic energy based on the TGA data (Fig. 6), where every variable was covered by a single line. The activation energy (E) can be calculated using the slope of the straight line. The activation energy (E) was calculated to be around 25.35 kJ mol⁻¹. Reaction rate will decrease because it will be harder to start the reaction process with higher activation energy. The low activation energy demonstrates the weak bonds that exist between volatile chemicals and biomolecules. The activation energies obtained by RPP with various raw materials from the literature are compared in Table 3.

Fig. 6.

Coats–Redfern plot of rose petal’s plasticizers

Table 3.

Comparison of the RPP activation energies with various source materials from the literature

Sl. No.	Materials	E (kJ mol−1)	References
1	Cassava starch	22.62	Wahyuningtiyas et al. (2017)
2	Poly(3-hydoxyalkanoates)	85.3	Sin et al. (2010)
3	Ficus religiosa	68.02	Moshi et al. (2020)
4	Cymbopogon flexuosus	73.01	Raja et al. (2022)
5	RPP	25.34	This work

AFM

Using AFM imaging, the RPP's microstructure was also described on a smaller scale. Topographical contrast was used to capture the photographs. It has been utilized to provide qualitative and quantitative information about biomolecules at the nanoscale scale that is frequently not accessible by any other experimental technique. The AFM technique is a potent tool for researching surfaces. In Fig. 7, RPP AFM pictures with a two-dimensional and three-dimensional surface were shown. On the surface, a number of pointed peaks with deeper valleys are dispersed throughout the area. The plasticizer's morphology and roughness were examined using AFM. In Fig. 7a, b, respectively, the contrast mode microscopic operations created sizes of 10 × 10 μm and 2.5 × 2.5 μm for the three-dimensional image. The red line profile and the red power spectrum profile are shown on the X and Y axes in Fig. 7c, d. These line profiles and power spectra show the surface parameters for 2D movement. The roughness parameters (Rpv, Ra, Rq, Rz, Rsk, and Rku) are displayed in Fig. 7e, f.

Fig. 7.

AFM image of Rose petals plasticizers a horizontal—3D and 2D profile, b vertical—3D and 2D profile

At the nanoscale, the peak values' maximum, minimum, midpoint, and mean are reported. In directions (X and Y), the average profile peak height and valley depth are R_pv = 47.042 nm and 31.698 nm, respectively. According to predictions, the average R_a (surface roughness) values for RPP would be 4.278 nm and 3.155 nm, respectively. Similar to this, the expected average R_q (Root Mean Square Surface Roughness) values for RPP were 6.771 nm and 5.060 nm, respectively. Due to the presence of lignin, hemicellulose, and wax-like components in the plasticizer, the lower values indicated that the surface of RPP was smooth. The difference between the highest and minimum peak heights is used to calculate the average absolute height roughness (R_z) value. The smooth areas of the plasticizer surface were, therefore, indicated by greater values of R_z 34.898 nm and 22.790 nm. Surface skewness (R_sk) and coefficient of kurtosis (R_ku) values both describe the symmetry of the surface profiles and the distribution of spikes above and below the mean line, respectively.

The porosity and load capacity of the surfaces are determined by the skew profile, and the negative sign of skewness is the ideal standard for good bearing surfaces (Yerramathi et al. 2021). A negative skewness (−2.289 and −2.619) was found in the current investigation, which indicates that the plasticizer's surface area has low peaks spread over it with a high carrying capacity. The surface of the plasticizer is porous when the skewness value is negative (Raja et al. 2022). Similar to how the spiky character of the surfaces is identified based on R_ku values, the values (9.045 and 11.548) in the current study are R_ku > 3 as a result of their spiky nature. This displays a few sparse low peaks and a deep valley and jerky surfaces with wax-like contents. The preceding result, therefore, supports the claim that an RPP with a smoother surface.

Morphological analysis by SEM

For the purpose of conducting the morphological investigation, micro structure pictures were created using a scanning electron microscope (SEM) at various magnifications, including 100×, 500×, and 5 k×. The significance of this study lies in its ability to determine if the plasticizer may be used in a particular polymer matrix application as an efficient reinforcing agent. It was also applied to investigate the morphology of the aggregation of RPP particles. SEM images show the shape and size of the particles. Figure 8 depicts images of the surface morphology of the RPP. The results showed that the shape of the RPP particle size is not uniform. At a 100× magnification, RPP shows randomly scattered, somewhat uneven surface particles. There were porous parts visible on the surface. Additionally, the RPP surface is not as rough. Granules make up surface characteristics. The black patch in Fig. 8a, which can be observed on the image, is recognised to be cavities in the concrete. The black patches between the particles in the photos are the material's open pores, which are evident from the images.

Fig. 8.

a–d Scanning electron microscopic images of Rose petals plasticizers at different magnification

RPP analyses have a ridged and grooved structure that is asymmetrical. Insufficient bonding between the components is indicated by the figure's few crack propagations. Poor interfacial adhesion, few voids, edges, and holes were found in the surface morphologies (Amin et al. 2019). The absence of agglomeration and the similar increase in surface area, which results in a significant number of active sites for binding with future polymers, are clearly visible. RPP's low molecular weight makes it easy for it to reach the interfaces between the components of biocomposite materials, allowing for compatibility and producing a surface that is overall smoother. Paul et al.'s findings and these results are fairly consistent (Paul et al. 2021).

A portion of the surface in Fig. 8b is rough and has a spiky appearance, which unquestionably favours the AFM analysis's findings. The partially rough surface and fissures in the RPP in Fig. 8c may be caused by the presence of hemicellulose and wax components, which are visible as white layers in the image. Although the presence of holes and debris reduces the fiber's tensile strength, it increases the surface roughness, which improves the interfacial attachment of the fibre to the matrix polymer. Despite the fact that this RPP has all the aforementioned benefits, which include easy plastic deformation and low brittleness, it is recommended that you use it as a bioplasticizer. ImageJ software was used to estimate the average size of the plasticizer particles, whose sizes varied. The average particle size was calculated using measurements taken of a total of 25 particles in micrometres. The average particle size was then calculated to be 17.08 ± 12.97 μm.

Thresholds can be established as monochromatic images to determine the size of the particles in the segmented image. Figure 9a shows the threshold capture of individual microplasticizer particles with a red–orange tint. Figure 9b displays the data for the plasticizer's particle size (mean and standard deviation values). The histogram plots in Fig. 9c display the size distribution analysis of particle size (μm) in relation to count. 40% of the plasticizer is between 0 and 10 μm in size, while the remaining plasticizer is made up of particles between 10 and 20 μm (24%), 20 μm and 30 μm (16%), 30 μm and 40 μm (12%), and 40 μand 50 μm (12%), respectively. The plasticizer has an average size of 17.079 μm and a standard deviation of 12.968 μm.

Fig. 9.

a Threshold capture of plasticizers, b particle size data, and c histogram plots of size distribution

EDX spectroscopy analysis

The elemental composition fingerprints and high resolution particle surface structure characteristics of the material were best obtained using SEM/EDS. The distribution of chemical elements on the surface of the RPP is shown in Fig. 10a, b in proportion to weight and atomic percent. It was possible to see the big peaks of oxygen and carbon. The RPP also includes trace amounts of sodium (16.05 wt%) and aluminium (3.89 wt%), as well as calcium and chlorine (~ 1 wt%). The greater non-cellulosic material content in RPP may be the cause of this. However, the percentage of oxygen and carbon was determined to be (47.99 and 28.95 wt%) and oxygen were discovered to be the major elements, which indicates the RPP is organic in origin. Six components that are non-toxic to living things were discovered in the manufactured plasticizer, according to a SEM/EDX investigation.

Fig. 10.

a Energy-dispersive X-ray spectrogram of plasticizers isolated from rose petals and b weight/atomic percentage of diverse elements of RPP

SEM with biofilm

Figure 11 shows the chemical bonding for this specific RPP plasticizer’s plasticization effect with PBAT—poly(butylene adipate-co-terephthalate) matrix. In Fig. 12a–h, the surface morphology of the biofilm enhanced with RPP/PBAT plasticizer is depicted. Figure 12a–d provides a concise and convincing explanation of the flexibility and transparency of the RPP plasticizer-reinforced biofilm. To visually assess the dispersion of RPPs in the matrix PBAT, the fracture surface of bio-nanocomposite films containing 5 wt% RPPs was examined using SEM, and should be visible in Fig. 12e–h. According to the microscopic pictures prior to the replenishment of bioplasticizers, pure PBAT biofilms had increased porosity, as seen by the yellow circle in Fig. 12e, g. Biofilms after the reinforcement of bioplasticizers are depicted in Fig. 12f, h. Table 4 denotes the properties of PBAT with and without reinforcement materials.

Fig. 11.

The plasticization effect of RPP plasticizer in PBAT matrix

Fig. 12.

a–h SEM images of RPP plasticizer-reinforced biofilm: a pure PBAT film, b PBAT/5% RPP plasticizer-reinforced biofilm, c flexibility confirmation of pure PBAT film, d flexibility confirmation of PBAT/5% RPP plasticizer-reinforced biofilm, e, g PBAT biofilm at ×100  and ×500  magnification, f, h PBAT/5% RPP plasticizer-reinforced biofilm at ×100  and ×500  magnification

Table 4.

Properties of PBAT with and without reinforcement materials

Polymer	Filler	Treatment	Filler loading (wt %)	Mechanical properties			References
				Tensile strength (MPa)	Young’s modulus (MPa)	Elongation at break (%)
PBAT	Native starch	Acetylation	20 40	7.28 15.47	101.01 95.30	107.5 170.81	Perumal et al. (2023)
PBAT	Thermoplastic starch	Acetylation	40	11.19	110.05	114.62	Perumal et al. (2023)
PBAT	Thermoplastic starch	Acetylation (DS 0.06)	20 50 100	6.7 6.7 2.7	N/A	188 22 96	Ivanič et al. (2019)
PBAT	Neat-			15.3	136	508	Ludwiczak et al. (2021)

Since RPP was well distributed throughout the PBAT matrix, its observation was more challenging overall, with the exception of the areas marked in the image. The RPP particles in Fig. 12h are shown by yellow circles, which are thought to be filled in porous areas of the surface without clearly showing any signs of aggregation. Films had no visible pores or cracks. RPP was used to fill the PBAT biofilm porous to reduce surface porosity and boost plasticizing effects. Surfaces of plasticized PBAT films with RPP were comparatively homogeneous (Bodîrlǎu et al. 2012), indicating that the combination of plasticizers RPP is completely miscible and compatible with the polymer matrix (Jun et al. 2020). The decreased interfacial gaps observed in the Fig. 12f, h following reinforcing is proof that the polymer and the fillers are compatible with one another.

The surface of the object appears to have some filled RPP, and the SEM photos show that the surface is uniform and comparatively smooth. The absence of pores and microcracks in significant portions of the surfaces of biofilms showed that they are more uniform, cogent, and smooth. Overall, the surface structure of PBAT films was improved by the addition of plasticizers at the proper concentrations, which also improved the coherence and integrity of the film. The homogeneity of the reinforced biofilms is an excellent indicator of their structural stability (Abotbina et al. 2021). The results of the current study show that the bio-plasticizers produced have good plasticizing qualities, biocompatible and biodegradable (Urbizo-Reyes et al. 2020). The effects of the different plasticizers on the production of biofilms are listed with their properties in Table 5. The plasticizing samples are an excellent substitute for conventional, non-biodegradable plasticizers because they are composed of natural, environmentally friendly building blocks. Although this study has several benefits, there are some restrictions to achieve our goal of applications. In the upcoming phase of our research, biodegradability tests and a life-cycle evaluation will be carried out to determine the precise use of food packaging materials. The yield of the bioplasticizer isolated from waste rose petals is relatively low while using the current methodologies, and the costs of producing bioplasticizers are significantly higher than those of synthetic plasticizers. To address these issues, efforts are being made to improve the methodology to reduce costs and increase yields of bioplasticizers.

Table 5.

Effect of various plasticizers reinforcement on biofilm properties with different matrix

Plasticizer	Polymer	Filler loading (wt %)	Mechanical properties			Physical properties		Solubility parameters		References
			Tensile strength (MPa)	Young’s modulus (MPa)	Elongation at break (%)	Thickness (µm)	Density (g/cm3)	Moisture content (%)	Solubility (%)
Fructose	Wheat starch-based films	15 25 35	18.99 12 7.6	822.22 435.83 152.54	9.41 17.2 47.5	156.40 177.60 200.20	1.59 1.47 1.39	8.70 8.17 9.15	14.92 22.62 29.02	Mohammed et al. (2022)
Glycerol		15 25 35	22.8 6.35	1119 199.19 68.76	4.4 46.1 47.2	176.60 205.20 207.60	1.55 1.37 1.34	12.14 13.67 20.58	12.92 19.27 20.00
Sorbitol		15 25 35	25.3 6.35	1230.35 310.23 121	3.3 34.1, 60.7	155.0 175.20 189.60	1.55 1.49 1.48	10.38 10.47 9.90	15.19 22.06 28.00
Urea		15 25 35	5.64 1.12	224.14 12.367 6.56	32.3 50.4 54.1	170.20 190.40 207.60	1.48 1.45 1.07	11.48 16.98 21.53	13.29 17.81 20.42
Without plasticizer		–	–	–	–	170.20	1.32	11.86	2.54%
Glycerol	Chitosan	5 20 40	59.5 31.8 22.0	NA	19.1 45.7 84.2	NA	NA	13.7 15.8 24.3	NA	Suyatma et al. (2005)
Ethylene glycol		5 20 40	53.7 34.0 33.2	NA	16.8 38.1 67.0	NA	NA	13.9 14.5 14.0	NA
Polyethylene glycol		5 20 40	65.1 40.6 36.6	NA	12.1 42.2 79.7	NA	NA	13.2 21.9 22.1	NA
Propylene glycol		5 20 40	74.2 44.6 36.3	NA	6.4 36.6 44.3	NA	NA	14.9 15.5 14.9	NA
Without plasticizer		–	63.1	–	7.2	–	–	14.4	–
Triethyl citrate	PLA-microcrystalline cellulose (1:1)	5 10 15	11.80	2495 563 22	1.70 25.97 299.78	NA	NA	NA	NA	Paul et al. (2021)
Triethyl citrate	PLA	5 10 15	NA	1553 1368 161	9.74 13.00 595.19	NA	NA	NA	NA
Ferulic acid	Sodium alginate films	FA 150 FA 210 FA 270	22.22 28.38 29.67	NA	7.46 6.60 6.13	276 273 276	NA	87.60 87.20 87.00	68.35 61.50 57.32	Yerramathi et al. (2021)
Glycerol	Arrowroot starch	15 30 45	9.34 2.42 1.95	620.79 52.26 36.08	2.41 46.62 57.33	156 163 208	1.43 1.33 1.32	9.60 9.77 13.03	14.86 21.62 29.50	Tarique et al. (2021)
Triester-amide thiophene	Poly(vinyl chloride)	10 20 30 40 50	45.92 44.72 42.60 27.48 19.27	1771.58 1426.91 1091.61 851.76 561.40	2.52 5.40 28.68 89.2 143.92	NA	NA	NA	NA	Satavalekar et al. (2016)
Fructose	Cornstarch-based films	25 40 55	6.8 NA 3.8	61 30 28	NA	195 395 419	1.56 1.22 0.99	11.13 20.60 24.02	21.38 33.92 42.98	Ibrahim et al. (2019)
Sorbitol		25 40 55	4.52 NA 3.04	32 28 17	NA	295 314 317	1.147 1.483 1.657	17.28 18.01 17.88	40.07 44.14 47.68
Urea		25 40 55	0.62 NA 0.04	1.2 0.05 0.01	NA	297 298 334	1.459 1.888 5.454	21.05 26.08 27.86	24.48 63.99 90.67

Conclusions

Biopolymer-based composites are very popular today as they are widely used in a number of sectors without compromising environmental standards. The use of biodegradable polymers, which are sustainable and have abundant plant resources, has been encouraged by the current improved environmental awareness. A suitable chemical and environmentally safe approach was adopted to separate the natural plasticizers from rose petals for this study. Chemical investigation of IR spectral analysis confirmed the existence of specific functional groups such as carbonyl (1639 cm⁻¹), hydroxyl (broad peak at 3451 cm⁻¹), indicating the presence of a secondary phenolic derivative such as flavonides in the RPP biomass. The absorbance at 227.4 nm and the other peaks in the range of 310 to 400 nm corresponding to band I of flavonoids can be attributed to band II of flavonoids in the UV spectrum of RPP biomass. The crystallinity size (CS) and crystallinity index (CI) values for the RPP are determined as 9.36 nm and 23.87%, respectively, from the XRD data. The weight loss at higher temperatures, as shown by the TGA, and the maximum degradation, as shown by the DTG curve, occurred at 343 °C. The degradation above this temperature, which can be explained by the oxidation and decomposition of char to low molecular weight gaseous compounds, was caused at 343 °C by depolymerization, dehydration and decomposition of hydroxyl units followed by char production. Thermal experiments of the same type were also carried out for various biopolymers. The average Ra values (surface roughness) for RPP are 4.278 nm and 3.155 nm, respectively. The above result, therefore, supports the claim that an RPP has a smoother surface. The absence of agglomeration and the similar increase in surface area leading to a considerable number of active sites for binding with future polymers are clearly visible. The low molecular weight of RPP facilitates reaching the interfaces between the components of biocomposite materials, ensuring compatibility and providing an overall smoother surface. a biofilm reinforced with 5% RPP and a pure PBAT film were formulated and characterized to determine the plasticization and film-forming ability of RPP. RPP-reinforced films showed good surface compatibility and more flexibility than PBAT-only films. The ability of the new bioplastics to be plasticized was demonstrated when they were reinforced with a biodegradable PBAT polymer matrix for biofilm applications. It was found that the properties of RPP indicate that it could be a good plasticizer for overcoming upcoming environmental problems. As the current study suggests that the bio-plasticizer obtained is a better alternative to synthetic, harmful plasticizers for future lightweight packaging applications.

Author contributions

All authors are equally contributed to Conceptualization, Methodology, Writing—original draft, Writing—review & editing.

Funding

This research was funded by the National Science, Research and Innovation Fund (NSRF), and King Mongkut’s University of Technology North Bangkok with Contract no. KMUTNB-FF-67-B-56.

Data availability

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Declarations

Conflict of interest

The author(s) declared no competing interest with respect to the research, authorship, and/or publication of this article. The authors have no conflicts of interest to declare that are relevant to the content of this article.

Ethical approval

Not applicable.