dk-4202 for improved weather resistance in plastics

introduction

the durability and longevity of plastic materials exposed to outdoor environments are critical concerns across multiple industries, including automotive, construction, packaging, and consumer goods. ultraviolet (uv) radiation, temperature fluctuations, moisture, and atmospheric pollutants can cause significant degradation in polymers, leading to discoloration, loss of mechanical strength, surface cracking, and embrittlement. to combat these effects, the use of advanced weathering stabilizers has become essential in formulating high-performance plastics. among these, dk-4202—a high-efficiency light stabilizer based on hindered amine light stabilizer (hals) chemistry—has emerged as a leading additive for enhancing the weather resistance of a wide range of plastic materials.

this article provides a comprehensive overview of dk-4202, detailing its chemical structure, mechanism of action, technical specifications, and performance benefits in various polymer systems. drawing on both international and domestic research, the discussion includes comparative studies, real-world applications, and formulation guidelines. the aim is to offer material scientists, engineers, and product developers a detailed understanding of how dk-4202 contributes to extended service life and improved aesthetics in outdoor-exposed plastic products.

chemical structure and mechanism of action

dk-4202 belongs to the class of hindered amine light stabilizers (hals), which are among the most effective additives for protecting polymers against photo-oxidative degradation. unlike uv absorbers that function by screening or absorbing harmful uv radiation, hals compounds operate through a catalytic mechanism that interrupts the radical chain reactions responsible for polymer breakn.

the active moiety in dk-4202 is a tetramethylpiperidine derivative, which undergoes oxidation in the presence of free radicals (such as alkyl, alkoxy, and peroxy radicals) generated during uv exposure. the resulting nitroxyl radical (no•) acts as a scavenger, deactivating destructive radicals and regenerating itself in a cyclic process. this catalytic regeneration allows dk-4202 to provide long-term protection even at low concentrations.

key steps in the stabilization mechanism:

1. formation of nitroxyl radical:
   r2n−h+roo•→r2n•+roohr2​n−h+roo•→r2​n•+rooh
2. radical scavenging:
   r2n•+r′•→r2n−r′r2​n•+r′•→r2​n−r′
3. regeneration via secondary reactions:
   the stabilized amine is continuously regenerated, enabling sustained protection.

this mechanism is particularly effective in polyolefins (pp, hdpe, ldpe), polyurethanes (pu), and engineering plastics such as polycarbonate (pc) and abs.

technical specifications and product parameters

dk-4202 is typically supplied as a white to off-white free-flowing powder with excellent thermal stability and compatibility with a broad range of polymers. below is a detailed table of its key physical and chemical properties:

parameter	value/range
chemical name	bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate
cas number	52843-67-7
molecular weight	569.96 g/mol
appearance	white to off-white powder
melting point	85–92°c
solubility in water	<0.1 g/l (practically insoluble)
solubility in organic solvents	soluble in toluene, chloroform, thf
thermal stability	stable up to 280°c
recommended dosage	0.1–0.5 phr (parts per hundred resin)
volatility	low
regulatory status	compliant with fda 21 cfr 178.2010 (indirect food contact), reach, rohs

table 1: technical parameters of dk-4202

the low volatility and high thermal stability make dk-4202 suitable for high-temperature processing methods such as extrusion, injection molding, and blow molding without significant loss of activity.

performance benefits in polymer systems

1. polyolefins (pp, pe)

polyolefins are widely used in outdoor applications such as agricultural films, geomembranes, and automotive components. however, they are highly susceptible to uv-induced degradation due to the presence of tertiary carbon atoms in their backbone.

dk-4202 significantly enhances the outdoor durability of polyolefins. a study by wang et al. (2020) demonstrated that ldpe films containing 0.3 phr of dk-4202 retained over 85% of their tensile strength after 2,000 hours of xenon arc weathering, compared to only 50% retention in unstabilized samples.

polymer	additive loading (phr)	tensile strength retention (%) after 2000h quv	color change (δe)
ldpe	0	50	8.2
ldpe	0.3 dk-4202	85	2.1
pp	0	45	9.5
pp	0.4 dk-4202	80	2.8

table 2: weathering performance of dk-4202 in polyolefins (data adapted from wang et al., 2020)

2. engineering plastics (pc, abs, pa)

in engineering plastics, uv exposure can lead to yellowing and loss of impact strength. dk-4202 is effective in maintaining color stability and mechanical integrity. for example, in abs used for automotive grilles, the addition of 0.2 phr dk-4202 reduced yellowing index (yi) by 70% after accelerated aging (1,500 h, 60°c, 70% rh).

3. polyurethanes (pu)

coatings and elastomers based on pu are prone to chalking and cracking under uv exposure. dk-4202 helps preserve surface gloss and flexibility. a european study (schmidt & müller, 2019) showed that pu coatings with dk-4202 maintained 90% gloss retention after 3,000 hours of florida weathering, outperforming benzotriazole-based uv absorbers.

synergistic effects with other additives

dk-4202 exhibits excellent compatibility and synergy with other stabilizers, enhancing overall performance:

• with uv absorbers (e.g., benzophenones, benzotriazoles): while hals like dk-4202 do not absorb uv light, combining them with uv absorbers provides a dual-defense mechanism—absorption at the surface and radical scavenging throughout the bulk.
• with antioxidants (e.g., irganox 1010): primary antioxidants prevent initial oxidation, while dk-4202 handles subsequent radical propagation, offering comprehensive protection.
• with pigments (e.g., tio₂, carbon black): these pigments provide physical uv shielding, and dk-4202 complements them by stabilizing the polymer matrix.

a typical synergistic formulation for outdoor pp fibers:

• 0.2 phr dk-4202
• 0.1 phr tinuvin 328 (uv absorber)
• 0.1 phr irganox 1076 (antioxidant)
• 2.0 phr rutile tio₂

this combination extended the service life of the fibers by over 300% in accelerated weathering tests.

applications across industries

1. automotive

in exterior components such as bumpers, mirror housings, and trim, dk-4202 helps maintain color and mechanical properties over extended periods. oems like toyota and volkswagen have adopted dk-4202-containing formulations in their material specifications for improved durability.

2. construction

pvc win profiles, roofing membranes, and cladding materials benefit from dk-4202’s ability to resist yellowing and embrittlement. in china, major pvc profile manufacturers such as kingfa and sinochem have incorporated dk-4202 into their premium product lines.

3. agriculture

greenhouse films and mulch films require long-term uv resistance. dk-4202 extends the functional life of these films, reducing replacement frequency and environmental impact.

4. consumer goods

outdoor furniture, garden tools, and electronic housings rely on dk-4202 to maintain aesthetic appeal and structural integrity under prolonged sun exposure.

comparative analysis with other stabilizers

stabilizer type	mechanism	advantages	limitations	compatibility with dk-4202
benzotriazole uvas	uv absorption	immediate surface protection	can migrate; limited depth protection	high (synergistic)
benzophenone uvas	uv absorption	broad uv spectrum coverage	yellowing at high loadings	high
nickel quenchers	energy transfer	effective in thin films	toxicity concerns; dark color	low (antagonistic)
other hals (e.g., tinuvin 770)	radical scavenging	similar mechanism	may have higher volatility	high

table 3: comparison of light stabilizers

dk-4202 stands out for its low volatility, high efficiency at low dosages, and broad compatibility, making it a preferred choice in modern stabilization packages.

regulatory and environmental considerations

dk-4202 complies with major global regulations:

• reach (eu): registered and evaluated for safe use.
• rohs directive: free of restricted heavy metals.
• fda 21 cfr: permitted for indirect food contact applications.
• china gb standards: compliant with gb/t 26394-2011 for light stabilizers in plastics.

environmental studies indicate that dk-4202 has low aquatic toxicity and is not bioaccumulative, supporting its use in sustainable product designs.

challenges and future outlook

despite its advantages, challenges remain:

• acidic environment sensitivity: hals can be deactivated by acidic components (e.g., certain flame retardants or pigments).
• cost: higher than basic antioxidants, though justified by performance gains.

future research is focusing on:

• microencapsulation to improve compatibility and reduce interactions.
• hybrid molecules combining hals and uv absorber functionalities.
• recyclability studies to ensure performance retention in recycled plastics.

conclusion

dk-4202 represents a significant advancement in the stabilization of plastics for outdoor applications. its hindered amine chemistry provides long-term, catalytic protection against uv-induced degradation, preserving both mechanical and aesthetic properties. supported by extensive research and industrial validation, dk-4202 has proven effective in polyolefins, engineering plastics, and coatings, offering a reliable solution for manufacturers seeking durable, high-performance materials. as environmental and performance demands continue to rise, additives like dk-4202 will play an increasingly vital role in the evolution of sustainable polymer technologies.

references

1. wang, l., zhang, y., & liu, h. (2020). “performance evaluation of hindered amine light stabilizers in polyethylene films under accelerated weathering.” polymer degradation and stability, 178, 109185.
2. schmidt, a., & müller, k. (2019). “long-term outdoor durability of polyurethane coatings: a field and laboratory study.” progress in organic coatings, 135, 123–131.
3. li, x., chen, j., & zhou, m. (2021). “application of dk-4202 in automotive plastics: a case study from chinese oems.” china plastics, 35(4), 45–52.
4. karlsson, a., & hedenberg, ö. (2018). “synergistic effects of hals and uv absorbers in polypropylene.” journal of vinyl and additive technology, 24(3), 201–209.
5. iso 4892-2:2013. plastics — methods of exposure to laboratory light sources — part 2: xenon-arc lamps.
6. astm g154-17. standard practice for operating fluorescent ultraviolet (uv) lamp apparatus for exposure of nonmetallic materials.
7. gb/t 26394-2011. light stabilizers for plastics — classification and naming.
8. technical bulletin. (2022). tinuvin and chimassorb product guide. ludwigshafen: se.
9. cytec industries inc. (2020). hals technology: mechanisms and applications in polymer stabilization. west paterson, nj.
10. european chemicals agency (echa). (2023). reach registration dossier for cas 52843-67-7. https://echa.europa.eu/