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Insect trapped in resin
Cedar of Lebanon cone showing flecks of resin as used in the mummification of Egyptian Pharaohs

A resin is a solid or highly viscous liquid that can be converted into a polymer.[1] Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds insoluble in water, predominantly terpenes. Technically, resins should not be confused with gums, which consist predominantly of water-soluble polysaccharides, although these two terms are often interchangeable in the less formal context. Common resins include pine oleoresins, amber, hashish, frankincense, myrrh and the animal-derived resin, shellac. Resins are used in varnishes, adhesives, food additives, incenses and perfumes.

Resins protect plants from insects and pathogens, and are secreted in response to injury. Resins repel herbivores, insects, and pathogens, while the volatile phenolic compounds may attract benefactors such as predators of insects that attack the plant.[2]

Composition

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Most plant resins are composed of terpenes. Specific components are α-pinene, β-pinene, 3-carene, and sabinene, the monocyclic terpenes limonene and terpinolene, and smaller amounts of the tricyclic sesquiterpenes, longifolene, caryophyllene, and cadinene. Some resins also contain a high proportion of resin acids. Rosins on the other hand are less volatile and consist of diterpenes among other compounds.[citation needed]

Examples

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Examples of plant resins include amber, Balm of Gilead, balsam, Canada balsam, copal from trees of Protium copal and Hymenaea courbaril, dammar gum from trees of the family Dipterocarpaceae, dragon's blood from the dragon trees (Dracaena species), elemi, frankincense from Boswellia sacra, galbanum from Ferula gummosa, gum guaicum from the lignum vitae trees of the genus Guaiacum, kauri gum from trees of Agathis australis, hashish (Cannabis resin) from Cannabis indica, labdanum from mediterranean species of Cistus, mastic (plant resin) from the mastic tree Pistacia lentiscus, myrrh from shrubs of Commiphora, sandarac resin from Tetraclinis articulata, the national tree of Malta, styrax (a Benzoin resin from various Styrax species) and spinifex resin from Australian grasses.

Amber is fossil resin (also called resinite) from coniferous and other tree species. Copal, kauri gum, dammar and other resins may also be found as subfossil deposits. Subfossil copal can be distinguished from genuine fossil amber because it becomes tacky when a drop of a solvent such as acetone or chloroform is placed on it.[3] African copal and the kauri gum of New Zealand are also procured in a semi-fossil condition.

Rosin

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See also: Rosin
Extremely viscous resin extruding from the trunk of a mature Araucaria columnaris.

Rosin is a solidified resin from which the volatile terpenes have been removed by distillation. Typical rosin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-odorous or having only a slight turpentine odour and taste. Rosin is insoluble in water, mostly soluble in alcohol, essential oils, ether, and hot fatty oils. Rosin softens and melts when heated and burns with a bright but smoky flame.

Rosin consists of a complex mixture of different substances including organic acids named the resin acids. Related to the terpenes, resin acid is oxidized terpenes. Resin acids dissolve in alkalis to form resin soaps, from which the resin acids are regenerated upon treatment with acids. Examples of resin acids are abietic acid (sylvic acid), C20H30O2, plicatic acid contained in cedar, and pimaric acid, C20H30O2, a constituent of galipot resin. Abietic acid can also be extracted from rosin by means of hot alcohol.

Rosin is obtained from pines and some other plants, mostly conifers.[4] Plant resins are generally produced as stem secretions, but in some Central and South American species of Dalechampia and Clusia they are produced as pollination rewards, and used by some stingless bee species in nest construction.[5][6] Propolis, consisting largely of resins collected from plants such as poplars and conifers, is used by honey bees to seal small gaps in their hives, while larger gaps are filled with beeswax.[7]

Petroleum- and insect-derived resins

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Shellac is an example of an insect-derived resin.

Asphaltite and Utah resin are petroleum bitumens.

History and etymology

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The material dripping from an almond tree looks confusingly like resin, but actually is a gum or mucilage, and chemically very different.

Human use of plant resins has a long history that was documented in ancient Greece by Theophrastus, in ancient Rome by Pliny the Elder, and especially in the resins known as frankincense and myrrh, prized in ancient Egypt.[8] These were highly prized substances, and required as incense in some religious rites.

The word resin comes from French resine, from Latin resina "resin", which either derives from or is a cognate of the Greek ῥητίνη rhētínē "resin of the pine", of unknown earlier origin, though probably non-Indo-European.[9][10]

The word "resin" has been applied in the modern world to nearly any component of a liquid that will set into a hard lacquer or enamel-like finish. An example is nail polish. Certain "casting resins" and synthetic resins (such as epoxy resin) have also been given the name "resin".

Some naturally derived resins, when soft, are known as 'oleoresins', and when containing benzoic acid or cinnamic acid they are called balsams. Oleoresins are naturally occurring mixtures of an oil and a resin; they can be extracted from various plants. Other resinous products in their natural condition are a mix with gum or mucilaginous substances and known as gum resins. Several natural resins are used as ingredients in perfumes, e.g., balsams of Peru and tolu, elemi, styrax, and certain turpentines.[4]

Non-resinous exudates

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Other liquid compounds found inside plants or exuded by plants, such as sap, latex, or mucilage, are sometimes confused with resin but are not the same. Saps, in particular, serve a nutritive function that resins do not.

Resin of pine

Uses

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Plant resins

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Plant resins are valued for the production of varnishes, adhesives, and food glazing agents. They are also prized as raw materials for the synthesis of other organic compounds and provide constituents of incense and perfume. The oldest known use of plant resin comes from the late Middle Stone Age in Southern Africa where it was used as an adhesive for hafting stone tools.[11]

Lumps of dried frankincense resin
Caranna, a hard, brittle, resinous gum from species of Protium

The hard transparent resins, such as the copals, dammars, mastic, and sandarac, are principally used for varnishes and adhesives, while the softer odoriferous oleo-resins (frankincense, elemi, turpentine, copaiba), and gum resins containing essential oils (ammoniacum, asafoetida, gamboge, myrrh, and scammony) are more used for food and incense.[citation needed] The resin of the Aleppo pine is used to flavor retsina, a Greek resinated wine.[12]

Animal resins

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While animal resins are not as common as either plant or synthetic resins some animal resins like lac (obtained from Kerria lacca) are used for applications like sealing wax in India,[13] and lacquerware in Sri Lanka.[citation needed]

Synthetic resins

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Main article: Synthetic resin

Many materials are produced via the conversion of synthetic resins to solids, such as bisphenol A diglycidyl ether – a resin converted to epoxy glue upon the addition of a hardener. Silicones are often prepared from silicone resins via room temperature vulcanization. Alkyd resins are used in paints and varnishes and harden or cure by exposure to oxygen in the air.[14]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Resin

View on Grokipedia
from Grokipedia
Resin refers to a class of solid or highly viscous organic substances, either of or synthetic origin, that are typically amorphous and convertible into polymers through processes like curing or . resins are derived from exudates, such as the hardened of trees, forming water-insoluble mixtures of compounds primarily from and other , often exhibiting fusible, flammable, and translucent properties ranging from yellowish to brown in color. , in contrast, are industrially produced viscous materials that harden into rigid polymers, usually containing reactive end groups such as acrylates or epoxides, and are engineered to replicate or enhance the characteristics of their counterparts. Historically valued for their adhesive and protective qualities, natural resins like , , and dammar have been harvested for millennia and continue to be used in applications such as varnishes, lacquers, , and perfumes due to their in organic solvents and aromatic properties. These materials are noncrystalline and semi-solid, providing durability in traditional crafts and conservation efforts, including as materials for artworks and artifacts. Synthetic resins, developed in the early to meet industrial demands, dominate modern manufacturing and include types like , , and phenolic resins, which offer superior strength, chemical resistance, and versatility. The versatility of resins has made them indispensable across industries, with natural variants supporting sustainable and biodegradable alternatives in adhesives and coatings, while synthetic ones enable innovations in plastics, composites, , and biomedical applications such as systems and scaffolds. Their polymerization chemistry allows precise control over properties like hardness and flexibility, driving advancements in and environmental applications.

Definition and Composition

Chemical Structure

Resins encompass a diverse class of amorphous organic substances whose chemical structures vary by origin, but they generally consist of complex mixtures of hydrocarbons and oxygenated compounds. In natural resins, derived primarily from exudates, the molecular makeup is dominated by and terpenoids, which are isoprenoid-derived hydrocarbons built from C5 units, alongside phenolic compounds featuring aromatic rings with hydroxyl substitutions. Terpenoids in these resins include monoterpenes (C10, such as ), sesquiterpenes (C15, like cadinene), diterpenes (C20, e.g., ), and triterpenes (C30, such as ), often modified with functional groups to enhance stability and bioactivity. Phenolic components, including and simple phenols like derivatives, contribute to the resins' properties and rigidity through bonding. Petroleum-derived resins, a subset of synthetic variants, feature hydrocarbon-based structures primarily composed of aliphatic and aromatic chains polymerized from feedstocks. Aliphatic petroleum resins arise from C5 monomers like piperylene and , forming branched or linear polyolefin-like chains with molecular weights typically between 500 and 2000 Da. Aromatic variants, derived from C9 streams including styrene and indene, incorporate rings and fused aromatics, yielding more rigid structures due to π-π interactions and higher temperatures. Synthetic resins, engineered for specific applications, rely on long chains formed through or , often with cross-linking to achieve thermoset properties. resins, for instance, consist of ester linkages (-COO-) between diols and dicarboxylic acids, creating flexible yet durable chains; unsaturated variants include styrene for radical cross-linking. resins exemplify cross-linked structures, featuring rings (three-membered oxiranes) attached to backbones like diglycidyl ether of (DGEBA), where provides a phenolic core with two methyl bridges and hydroxyl groups (C15H16O2 unit). These groups react with hardeners to form extensive three-dimensional networks via ring-opening. Across resin types, functional groups such as hydroxyl (-OH) and carboxyl (-COOH) play pivotal roles in dictating reactivity, polarity, and intermolecular interactions. Hydroxyl groups enable hydrogen bonding, improving and in polar solvents, while carboxyl groups facilitate esterification or , influencing pH-dependent behaviors and cross-linking efficiency. In natural and synthetic contexts alike, these groups often terminate chains or pendant from backbones, modulating and thermal stability without altering the core framework.

Natural vs. Synthetic Distinctions

Natural resins are biogenic exudates secreted by or animals, functioning as protective barriers against injury or pathogens, and are typically composed of complex mixtures of compounds. These materials often include impurities such as waxes, volatile oils, and other organic residues that can affect their stability and processing. In contrast, are artificially produced polymers formed by linking monomers into chains, offering greater compositional uniformity and the ability to tailor properties like or heat resistance through controlled . A primary distinction lies in their renewability: natural resins derive from renewable biological sources, such as living plants and animals, contributing to a lower and biodegradability under certain conditions. , however, are predominantly manufactured from non-renewable feedstocks, raising concerns about and environmental persistence, though they provide superior consistency and scalability for industrial use. Emerging overlaps between the two categories include bio-based , which mimic resin behaviors by using renewable monomers like derived from processes to produce polymers such as poly(). These hybrid materials aim to combine the of origins with the engineered durability of synthetics, though they may still exhibit variability in purity similar to their biogenic counterparts.

Physical and Chemical Properties

Solubility and Viscosity

The solubility of resins, defined as the ability to dissolve in a to form a homogeneous solution, varies significantly between natural and synthetic types and is fundamentally governed by the principle of "like dissolves like," where and solute polarities must align for effective dissolution. Natural resins, such as and dammar, which are non-polar or weakly polar due to their and compositions, exhibit high in non-polar organic s like and , but remain insoluble in ; for instance, dissolves readily in to form varnishes used in traditional applications. Synthetic resins, including uncured epoxies and polyesters, often display greater polarity from functional groups like or linkages, enabling in polar s such as acetone or methyl ethyl ketone (MEK); however, this is limited to the monomeric or low-molecular-weight forms before curing. Hansen Parameters (HSP), which quantify dispersion, polar, and hydrogen-bonding interactions, provide a predictive framework for resin- compatibility, with natural resins like dammar having HSP values around (δD 18.8, δP 5.5, δH 4.0) that match -like s, while synthetics like align with acetone (δD 15.5, δP 10.4, δH 7.0). Viscosity, the measure of a fluid's resistance to flow under , is a critical for resin processing, particularly in their uncured, states where many exhibit non-Newtonian behavior—meaning changes with applied rather than remaining constant as in Newtonian fluids. For example, uncured resins often display shear-thinning characteristics, where decreases under increasing shear, facilitating easier handling and during composite fabrication, with typical values ranging from 500 to 10,000 mPa·s at depending on formulation. This non-Newtonian flow arises from molecular entanglements and, in filled systems, particle interactions, contrasting with the more Newtonian behavior of low- natural resin solutions. Several factors influence resin solubility and viscosity, with temperature being paramount: elevated temperatures generally enhance solubility by increasing molecular mobility and reduce viscosity exponentially, following an Arrhenius-like dependence (viscosity η ∝ e^{E_a / RT}), though excessive heat can accelerate unwanted curing. Additives, such as fillers or reactive diluents, can increase viscosity by up to 2.5 times per volume fraction in dilute suspensions (per Einstein's relation) or decrease it to improve flow, while solvent choice modulates both properties through polarity matching. Rheometry serves as the standard measurement technique, employing rotational viscometers or oscillatory rheometers with parallel-plate geometries to quantify viscosity across shear rates; for thermosets, dynamic oscillatory tests track the evolution from viscous (storage modulus G' < loss modulus G'') to elastic dominance during curing, with disposable plates preventing contamination from reactive samples. Curing profoundly alters these properties by converting soluble, low- monomers into crosslinked, insoluble , dramatically increasing from processable levels (e.g., <1,000 mPa·s) to near-infinite at the gel point, where the material transitions to a solid network. This cross-linking reduces , as evidenced in resin composites where longer curing times and higher temperatures (e.g., 60°C for 40-60 seconds) decrease compared to shorter exposures at 10°C, minimizing unreacted leaching and enhancing dimensional stability. The resulting thermoset structure, with high density, renders the resistant to solvents that dissolved its precursors, a transformation essential for applications requiring durability.

Thermal and Mechanical Behaviors

Resins exhibit distinct thermal behaviors depending on whether they are natural or synthetic, influencing their processing and application limits. For synthetic resins, such as epoxies and polyesters, the glass transition temperature (Tg) marks the shift from a rigid, glassy state to a more flexible, rubbery state, typically ranging from 50°C to 150°C for common formulations, though high-performance variants can exceed 200°C. This property is critical for determining operational temperatures in composites and adhesives, where exceeding Tg can lead to diminished structural integrity. Natural resins, in contrast, often soften or melt at lower temperatures; for instance, colophony (rosin), derived from pine trees, has a softening point around 70–100°C, allowing it to flow under moderate heat for uses like varnishes. Mechanically, resins demonstrate a spectrum of strength and deformability tailored to their cross-linking and composition. Cured resins, widely used in structural applications, typically achieve tensile strengths of 50–100 MPa, providing robust load-bearing capacity while maintaining some elasticity to absorb impacts without fracturing. This elasticity, quantified by values often between 2–3 GPa for epoxies, enables resins to undergo reversible deformation under stress, though highly cross-linked variants tend toward . resins like exhibit greater flexibility in their uncured state but harden to a brittle form upon drying, with tensile strengths typically lower than synthetics (e.g., 5–25 MPa for ). Under elevated temperatures, resins undergo degradation primarily through oxidation and , compromising their mechanical properties over time. Oxidative degradation in , such as epoxies, initiates chain scission and cross-linking at temperatures above 200–300°C, leading to embrittlement and loss of elasticity as oxygen reacts with backbones. occurs in phenolic resins during , forming a protective carbon residue that enhances fire resistance, though post-exposure mechanical properties may be compromised. These mechanisms highlight the need for stabilizers in high-heat environments to mitigate volatile release and structural weakening.

Natural Resins

Plant-Derived Resins

Plant-derived resins are amorphous, organic substances secreted by various trees as a defense mechanism against injury, pathogens, or herbivores, typically exuding from the bark, , or leaves and hardening upon exposure to air. These resins are primarily composed of compounds and are insoluble in but soluble in organic solvents. They are obtained from a wide range of woody plants, including and angiosperms, through methods such as , which involves making incisions in the trunk to collect the flowing , or to separate volatile components into balsams and gums. Oleoresin from pine trees (Pinus species), a prominent example of conifer-derived resin, is extracted via bark streaking or chipping techniques, where shallow cuts are made in the living tree trunk, often stimulated chemically to promote flow, and the exudate is collected in gutters or containers over several weeks. This crude oleoresin, a viscous mixture, is then processed by steam distillation to yield gum turpentine (volatile monoterpenes and sesquiterpenes) and gum rosin (nonvolatile diterpene acids). Conifer resins like pine oleoresin exhibit high terpene content, with monoterpenes such as α-pinene and β-pinene comprising up to 20-30% of the composition, alongside sesquiterpenes and diterpenoids that provide antimicrobial and antiherbivory properties. Resins from non-coniferous trees include , harvested from species () native to arid regions of and the , where incisions are made in the bark during the dry season to collect the milky that hardens into pale, translucent tears. However, overharvesting has resulted in declining populations, raising sustainability issues in production regions. This resin is rich in boswellic acids (triterpenoids) and can be further extracted via maceration in for bioactive compounds. resin originates from trees in the genus (), particularly in , obtained by tapping the trunks of species like Bursera copallifera, yielding a hard, aromatic used traditionally as ; its composition features α- and β-amyrin alongside sesquiterpenes. Dammar resin is sourced from trees, such as species in , through artificial wounding of the bark to collect the clear, hard , which contains dammarane triterpenoids and is valued for its varnish-forming properties. Amber represents a fossilized form of plant-derived resin, primarily from ancient in the Sciadopityaceae family during the Eocene , polymerized over millions of years into a hard, gem-like material often enclosing and inclusions. Unlike fresh resins, amber's composition is dominated by labdanoid diterpenes like communic acid, with contributing to its durability. , sometimes considered a semi-fossilized resin, shares similar origins but remains softer and more recent, bridging fresh exudates and fully fossilized types. These variations in composition, such as elevated levels in conifer resins versus triterpenoid dominance in angiosperm sources, reflect adaptations to specific ecological pressures.

Animal and Insect-Derived Resins

Animal and -derived resins are natural polymers primarily secreted or processed by , distinguishing them from direct plant exudates through their biological involvement in production. These resins often serve protective functions in the organisms' life cycles, such as encasing eggs or sealing habitats, and are harvested for human use in coatings, adhesives, and medicinal applications. Unlike plant resins, which form via mechanical injury or metabolic processes in trees, insect-derived varieties involve enzymatic modification or direct glandular secretion, resulting in unique compositions rich in esters, waxes, and bioactive compounds. Shellac, one of the most prominent insect-derived resins, is secreted by the female lac bug , a in the family , as a protective for its larvae and eggs while feeding on the sap of host trees like palas () and kusum ( oleosa). The resin forms a hard, encrusting layer on branches, which is harvested by scraping and processing into flakes or powder, yielding a composed mainly of esters of aleuritic, shellolic, and jalaric acids, along with minor amounts of butolic acid and free fatty acids. This composition imparts shellac's characteristic solubility in alcohol and use as a natural and polish in , pharmaceuticals, and food glazing, with global production centered in , which supplies more than 50% of the world's shellac. The lac bug's secretion process involves the metabolizing plant sugars into resinous polymers, highlighting the insect's role in bio-transforming plant-derived precursors into a distinct . Propolis, known as bee glue, is produced by honeybees (Apis mellifera) through the collection and modification of plant resins from buds, sap flows, and exudates of trees such as poplars and , which the bees masticate with salivary enzymes and mix with and to form a sticky, resinous substance. This processing alters the plant materials, incorporating bee-derived proteins and altering the phenolic and profiles, resulting in a heterogeneous mixture typically comprising 50% resins and balsams, 30% , 10% essential oils, 5% , and trace vitamins, , and minerals. Bees use propolis to seal hive cracks, embalm intruders, and inhibit microbial growth, leveraging its properties; in applications, it serves as a natural in tinctures and ointments due to its high content of bioactive like pinocembrin and galangin. The variability in propolis composition reflects regional , with European types often poplar-based and tropical variants drawing from diverse botanical sources. Rare examples of animal and -derived resins include the crimson pigments from lac scale insects, such as Kerria lacca, where the 's excretory products yield laccaic acids—polyketide-based metabolites that form a red pigment (lac dye) used in dyes, inks, and varnishes. These pigments originate from endosymbiotic fungi within the , which biosynthesize the compounds from plant-derived precursors, producing a vibrant red material distinct from plant-only resins. This insect-mediated production underscores the role of symbiotic interactions in generating unique resinous materials with applications in and art conservation.

Synthetic Resins

Polymerization Processes

Synthetic resins are primarily produced through two main polymerization mechanisms: chain-growth and step-growth polymerization. Chain-growth polymerization, also known as addition polymerization, involves the sequential addition of monomers to a growing polymer chain, typically without the release of byproducts, and is commonly used for resins like polyacrylates. In contrast, step-growth polymerization, or condensation polymerization, proceeds through stepwise reactions between functional groups on monomers, often eliminating small molecules such as water or alcohol, and is exemplified by polyester resins. These processes allow for the controlled synthesis of resins with tailored properties for industrial applications. Addition for polyacrylate resins relies on a free radical mechanism, where an initiator generates radicals that add to the double bonds of monomers, such as or , propagating the chain until termination occurs. This process typically employs , like benzoyl peroxide, as initiators to start the reaction by decomposing into free radicals under or light. The resulting polyacrylates exhibit high clarity and , making them suitable for coatings and adhesives. Free radical addition of acrylates is characterized by rapid propagation and can achieve high molecular weights, though it may lead to broad molecular weight distributions due to reactions. Condensation polymerization for resins involves the reaction between diols and dicarboxylic acids or their derivatives, forming linkages while releasing water or alcohol as byproducts. For instance, reacts with to produce (PET), a common polyester resin, through esterification and steps. Catalysts such as metal acetates or acids accelerate the reaction by facilitating proton transfer. This step-growth mechanism results in polymers with linear or branched structures, depending on functionality, and is often conducted under to remove byproducts and drive equilibrium toward higher molecular weights. In chain-growth processes like polymerization, the polymer chain extends rapidly from an active center, with concentration remaining high until late stages, whereas step-growth involves random of oligomers, leading to a broader distribution of chain lengths early on. Peroxides serve as versatile catalysts primarily in chain-growth mechanisms but can also influence reactions indirectly. These mechanistic differences affect resin processing, with chain-growth favoring bulk or techniques for uniform products. Post-2020 advancements in bio-based synthesis have integrated plant-derived monomers, such as itaconic acid from fermentation of glucose or sorbitol from corn, into both addition and condensation polymerizations to enhance sustainability. For example, radical polymerization of bio-based acrylates in aqueous media has yielded resins with comparable performance to petroleum-derived ones, reducing carbon footprints by up to 40% in some formulations. These developments emphasize renewable feedstocks like vegetable oils or lignin derivatives, enabling scalable production of eco-friendly polyesters and polyacrylates through modified chain- and step-growth routes. As of January 2025, new bio-based acrylic binders with up to 30% bio-content achieve up to 40% carbon footprint reduction compared to traditional resins.

Common Types and Formulations

Synthetic resins are broadly classified into thermosetting and thermoplastic types based on their response to heat during processing. Thermosetting resins undergo irreversible cross-linking upon curing, forming rigid networks, while thermoplastics soften upon heating and can be reshaped multiple times. Among thermosetting resins, epoxies are widely used due to their excellent and mechanical strength, with the most common formulation being diglycidyl ether of (DGEBA), synthesized from and . DGEBA is typically cured with hardeners, such as , to form a cross-linked network suitable for structural applications. Phenolic resins, another key thermosetting category, are produced by the of phenol and , yielding resole (one-stage) or novolac (two-stage) formulations. Resole phenolics are self-curing under and base catalysis, while novolacs require a hardener like for cross-linking, providing high thermal stability. Thermoplastic resins include acrylics, which are chain-growth polymers derived primarily from (MMA) monomers, often copolymerized with other for tailored properties like clarity and weather resistance. , which can be formulated as or thermosets, form another major group, synthesized from diisocyanates (e.g., isophorone diisocyanate) and polyols, resulting in flexible or rigid formulations depending on the chain extenders used. UV-curable variants of these thermoplastics, such as polyurethane acrylates (PUAs), incorporate acrylate end-groups for rapid photopolymerization, enabling formulations with low viscosity and high-speed curing under UV light, as seen in coatings derived from itaconic acid-based polyols. Specialty formulations of often involve nanocomposites, where nanofillers like silica (SiO₂) or carbon nanotubes are dispersed in an matrix to enhance strength without significantly increasing weight. For instance, adding 1-5 wt% multi-walled carbon nanotubes or nanofibers to resins can improve tensile strength by up to 30% through better load transfer and crack deflection mechanisms. These hybrid systems leverage the high surface area of nanofillers for superior interfacial bonding. Recent developments in the have focused on recyclable thermoset resins to address end-of-life challenges, incorporating dynamic covalent bonds like vitrimers in formulations for reprocessability while maintaining mechanical performance. Bio-based UV-curable thermosets from vegetable oils, such as , represent sustainable alternatives with recyclability via , reducing reliance on petroleum-derived monomers.

Historical Development

Ancient and Traditional Uses

The term "resin" derives from the Latin resina, which in turn traces back to the Greek rhētinē, referring specifically to the resinous exudates from pine trees. In , around 3000 BCE, resins played a crucial role in mummification processes, where gum resins such as and were employed for their preservative and aromatic properties to treat the body and wrappings. These materials, often imported from regions like the and , were mixed with other substances like cedar or pine resin to inhibit decomposition and imbue the deceased with a sacred scent believed to aid their journey to the . Resins were also integral to religious and practical applications in and , dating back to approximately 2000 BCE. In Mesopotamian cultures, such as those in during the Old Babylonian period, aromatic resins served as in temple rituals to honor deities and purify spaces, while birch and other resins functioned as early adhesives for tools and sealing . Similarly, in , resins like mastic and pitch were burned as in household and public ceremonies, and applied as adhesives in and artifact repair, reflecting their widespread utility in both sacred and everyday contexts. Traditional medicinal uses of resins, particularly resin, have been documented among various indigenous cultures for and treating skin ailments. For instance, Native American groups, including the Lakota, applied resin salves to sores, burns, and infections due to its and sticky properties that promoted closure and prevented further contamination. These practices, rooted in oral traditions and ethnobotanical knowledge, highlight resins' role as natural remedies long before formal .

Modern Synthesis and Advancements

The invention of in 1907 by Belgian-born chemist Leo Hendrik Baekeland marked the advent of fully , created through the of phenol and to produce a heat-resistant, moldable material that retained its shape after heating. This breakthrough, patented as the first thermosetting plastic, enabled of electrical insulators, jewelry, and household items, laying the foundation for the synthetic resin industry by replacing natural alternatives like . Baekeland's process, developed in his New York laboratory, emphasized controlled reaction conditions to avoid brittleness, influencing subsequent resin formulations. Following , synthetic resin production surged due to wartime innovations and postwar economic expansion, with global output growing from about 2 million tons in 1950 to over 15 million tons by 1970, driven by applications in consumer goods and . (PVC), first polymerized in the 1920s but scaled commercially in the 1940s, became a staple for pipes, flooring, and packaging due to its versatility and low cost, while polyesters like (PET) gained prominence in fibers and bottles through processes refined during the war for synthetic textiles. This era's boom, fueled by feedstocks and , transformed resins from niche materials to ubiquitous components in automobiles and appliances, with annual growth rates exceeding 15% in the 1950s. In the , research since 2015 has advanced biodegradable synthetic resins, such as (PHAs) and (PLA) derivatives, engineered via microbial fermentation and chemical modifications to degrade in soil or marine environments within months, addressing plastic waste accumulation. These innovations, including starch-blended polyesters with enhanced tensile strength up to 50 MPa, stem from of for higher yields and have been commercialized for and biomedical scaffolds. Concurrently, 3D-printing resins have evolved rapidly from 2020 to 2025, with (SLA) formulations incorporating biocompatible photopolymers like methacrylated that achieve resolutions below 50 microns and support applications. High-performance variants, such as flexible polyurethane-acrylate hybrids, now enable with elongation at break exceeding 200%, driven by UV-curable systems integrated into multi-material printers. Environmental concerns have prompted stringent regulations, including the European Union's REACH framework expansions in the 2020s, which restricted four additional (DEHP, DBP, BBP, and DIBP) in consumer plastics to 0.1% by weight starting in 2020, aiming to mitigate endocrine disruption risks. The EU further delayed but upheld a DEHP ban in medical devices until 2030, spurring development of phthalate-free alternatives like bio-based plasticizers in PVC resins. These measures, alongside global efforts to phase out persistent additives, have accelerated innovation in low-toxicity resins.

Applications and Uses

Industrial and Manufacturing Roles

Resins play a pivotal role in industrial and processes, particularly synthetic varieties like epoxies, alkyds, and silicones, which enable the production of durable, high-performance materials essential for modern applications. Increasingly, bio-based resins derived from renewable sources are being adopted in these sectors for their environmental benefits while maintaining high performance in composites and coatings. These materials are integral to large-scale due to their versatility in , , and structural enhancement, contributing significantly to sectors such as , automotive, and . The global resin market, encompassing both synthetic and processed natural types, is projected to reach approximately $623 billion by , with growth largely driven by demand from the automotive sector for lightweight components and advanced coatings. In manufacturing, resins are widely used as adhesives in composite materials, notably with carbon fiber reinforcements, to create lightweight yet strong structures for components. These provide superior adhesion, high strength-to-weight ratios, and resistance to environmental stresses, making them ideal for applications like fuselages and wings where performance under extreme conditions is critical. For instance, carbon fiber composites enhance fuel efficiency and structural integrity in . For coatings and paints, resins dominate industrial formulations, serving as the primary binder in a substantial portion of global production due to their excellent film-forming properties, durability, and cost-effectiveness. Alkyds, which are oil-modified polyesters, are employed in protective coatings for metals, automotive finishes, and architectural surfaces, offering good adhesion and weather resistance. They represent one of the most extensively used synthetic polymers in the coatings industry, facilitating efficient large-scale application in manufacturing lines. In electronics manufacturing, resins are crucial for encapsulation and potting, providing protective barriers around circuits and components to shield against moisture, dust, chemicals, and extremes. These resins to form flexible, insulating layers that maintain electrical integrity while accommodating component expansion, making them essential for devices in harsh environments like and consumer gadgets. Silicone encapsulants are particularly valued for their high stability and low stress on delicate parts.

Artistic, Medicinal, and Other Uses

In the realm of fine arts, resins have long served as essential components in and enamels for oil paintings, providing protective coatings that enhance color saturation and gloss while shielding surfaces from environmental damage. During the , artists employed natural tree resins such as mastic and , often combined with oils, to create durable mediums that allowed for glazing techniques and luminous effects in works by masters like . By the , dammar resin became a preferred varnish material in due to its clarity and reversibility, dissolving easily in to form thin, non-yellowing films that preserved the vibrancy of oil paintings. In modern practice, synthetic acrylic resins, particularly methacrylates and acrylates, have largely supplanted natural alternatives in varnishes, offering superior stability, UV resistance, and removability for conservation purposes without altering the artwork's appearance over time. Medicinally, resins derived from and have found applications in pharmaceuticals and supplements, leveraging their natural properties for and therapeutic benefits. , a resin secreted by the lac bug, is widely used as an for tablets, protecting sensitive medications from stomach acid and enabling targeted release in the intestines, a practice established since the early 20th century. , a bee-produced resinous mixture rich in , is incorporated into modern dietary supplements for its antimicrobial effects, particularly against like , supporting its use in oral health products and immune boosters. Beyond art and medicine, resins hold cultural significance in jewelry and ritual practices. , fossilized tree resin, has been crafted into beads and pendants since the , with artifacts from 8,000 BCE gravesites demonstrating its role as both adornment and amulet in ancient European and Mediterranean societies. resin, harvested from trees, is burned as in religious ceremonies across , , symbolizing and purification through its aromatic smoke that rises during rituals. In emerging applications, formulated for have revolutionized by enabling intricate sculptures and installations that blend digital design with physical form, as seen in works by artists like Morehshin Allahyari in the 2020s. More recent examples include Formlabs' November 2025 launch of Tough 1000 Resin and Tough 2000 Resin V2, which offer high impact strength and elongation for creating durable, functional pieces and installations. Natural resins also feature in , where and extracts provide anti-inflammatory and scent-stabilizing properties in perfumes and skincare formulations.

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