Plastics Materials (Part 5): In-depth Analysis of PP-LGF
Time：2026-10-21 08:25:14 / Popularity： / Source：
For previous reading, please refer to Plastic Materials (Part 4): In-depth Analysis of PP-GF.
PP-LGF (Long Glass Fiber Reinforced Polypropylene) is the highest-performance modified PP variety. Compared to short glass fibers (SGF), long glass fibers form a three-dimensional interwoven fiber network structure in product, resulting in more than just increased strength—it doubles impact toughness, improves fatigue resistance by 2-3 times, significantly improves creep resistance, and greatly enhances low-temperature toughness. With these advantages, PP-LGF has transformed from an experimental material for "plastics replacing metal" into preferred material for core structural components such as automotive front-end modules, seat frames, tailgates, battery trays, making it one of the most cost-effective solutions for automotive lightweighting.
PP-LGF (Long Glass Fiber Reinforced Polypropylene) is the highest-performance modified PP variety. Compared to short glass fibers (SGF), long glass fibers form a three-dimensional interwoven fiber network structure in product, resulting in more than just increased strength—it doubles impact toughness, improves fatigue resistance by 2-3 times, significantly improves creep resistance, and greatly enhances low-temperature toughness. With these advantages, PP-LGF has transformed from an experimental material for "plastics replacing metal" into preferred material for core structural components such as automotive front-end modules, seat frames, tailgates, battery trays, making it one of the most cost-effective solutions for automotive lightweighting.
I. What is PP-LGF? A Visual Guide
PP-LGF = PP matrix + Long Glass Fiber reinforcement, representing a high-end form of fiber-reinforced composite materials:
| Components | Functions |
| PP | Matrius material, transfers load, protects fibers, provides processability |
| LGF (Long Glass Fiber) | Reinforcing phase, forms a three-dimensional network, bears main load |
Number after LGF = percentage of long glass fiber mass. LGF20 = 20% long glass fiber, LGF30 = 30% long glass fiber, LGF40 = 40% long glass fiber.
Long Glass Fiber vs. Short Glass Fiber: Fundamental difference lies in fiber length.
Long Glass Fiber vs. Short Glass Fiber: Fundamental difference lies in fiber length.
| Comparison Items | Short Glass Fiber (SGF) | Long Glass Fiber (LGF) |
| Initial Fiber Length | 0.2-0.5 mm | 10-15 mm |
| Fiber Length After Injection Molding | 0.2-0.5 mm | 1-3 mm |
| Fiber Structure | Dispersed Short Fiber | Three-Dimensional Interwoven Network |
| Load Transfer | Single Fiber Load Bearing | Fiber Network Cooperative Load Bearing |
| Fracturing Mode | Fiber Pull-out, Brittle Fracture | Fiber Bridging, Progressive Failure |
Reinforcement principle of long glass fiber – three-dimensional network load-bearing.
Long glass fibers intertwine and entwine in product, forming a continuous three-dimensional fiber network:
External forces are quickly dispersed throughout structure through network → significantly improved load-bearing capacity. Crack propagation is blocked by multiple fibers → significantly improved impact toughness. Fiber network restricts matrix creep → good long-term dimensional stability. Fiber bridging effect → significantly extended fatigue life.
LGF vs. SGF: How much difference in performance?
External forces are quickly dispersed throughout structure through network → significantly improved load-bearing capacity. Crack propagation is blocked by multiple fibers → significantly improved impact toughness. Fiber network restricts matrix creep → good long-term dimensional stability. Fiber bridging effect → significantly extended fatigue life.
LGF vs. SGF: How much difference in performance?
| Performance Dimensions | SGF30 (Short Glass Fiber) | LGF30 (Long Glass Fiber) | Improvement rate |
| Tensile Strength | 80~100MPa | 90~120 MPa | +20-30% |
| Flexural Modulus | 5000~6500MPa | 5500~7500MPa | +10-20% |
| Notched Impact Strength | 8~12 kJ/m² | 20~30 kJ/m² | +200-300% |
| Unnotched Impact Strength | 30~50 kJ/m² | 50~80 kJ/m2 | +50-100% |
| Low Temperature Impact (-30℃) | Significantly Decreased | No significant decrease | Significant improvement |
| Fatigue Life | Benchmark | 2-3 times | +200-300% |
| Creep Resistance | Average | Excellent | Remarkable improvement |
| Dimensional Stability | Good | Better | Lower shrinkage rate |
| Surface Quality | Average (Floating Fiber) | Poor (more severe fiber floating) | Decrease |
| Processing Difficulty | Medium | Higher | More difficult |
Core conclusion: The biggest advantage of long glass fiber is not strength, but impact toughness and fatigue resistance – precisely performance most needed for structural components. Short glass fiber PP is a brittle material, while long glass fiber PP is a "quasi-tough" material.
PP-LGF vs PP-GF vs PP-TD vs PP+EPDM-TD: Full Spectrum Comparison
PP-LGF vs PP-GF vs PP-TD vs PP+EPDM-TD: Full Spectrum Comparison
| Comparison Dimensions | PP-LGF (Long Glass Fiber) | PP-GF (Short Glass Fiber) | PP-TD (Talc) | PP+EPDM-TD (toughening filler) |
| Tensile Strength | 90-120 MPa | 70-100 MPa | 30-40 MPa | 20-30MPa |
| Flexural Modulus | 5500-7500 MPa | 4000-6500 MPa | 2200-2800 MPa | 1700-2100MPa |
| Notched Impact | 20-30 kJ/m² | 8-12 kJ/m² | 3-8 kJ/m² | 15-30 kJ/m2 |
| Heat Deflection Temperature | 150-165℃ | 130-160℃ | 110-125℃ | 95-105℃ |
| Fatigue Resistance | Excellent | Good | Poor | Average |
| Creep Resistance | Excellent | Good | Average | Poor |
| Anisotropy | Strong | Strong | Medium | Weak |
| Surface Quality | Poor | Fairly Poor | Good | Good |
| Cost | Highest | Higher | Lowest | Medium |
| Typical Applications | Structural Components, Skeletons, Modules | Structural Components, Supports | Appliance housings, lamp housings | Bumpers, dashboards |
Arranged by long glass fiber content from low to high
LGF20 (20% Long Glass Fiber): LGF20 is an entry-level long glass fiber PP, offering significantly better impact toughness and fatigue resistance than short glass fiber PP while maintaining good flowability. It is suitable for structural components with medium loads and toughness requirements.
L vs H: L = Low melt index (low flow), good strength retention; H = High melt index (high flow), suitable for complex molds and large thin-walled parts.
LGF30 (30% Long Glass Fiber) – Most Commonly Used Grade: LGF30 is mainstream grade of PP-LGF, offering the best balance of strength, rigidity, toughness, and cost. It is preferred material for replacing steel with plastic in automotive structural components. SABIC Stamax series is benchmark product for global automotive LGF-PP.
LGF40 (40% Long Glass Fiber) – High Load Capacity: LGF40 is a high load capacity material with rigidity and strength approaching that of engineering plastics, used to replace metal in high-load-bearing structural components. However, its high glass fiber content makes processing more difficult and results in poorer surface quality.
LGF20 (20% Long Glass Fiber): LGF20 is an entry-level long glass fiber PP, offering significantly better impact toughness and fatigue resistance than short glass fiber PP while maintaining good flowability. It is suitable for structural components with medium loads and toughness requirements.
L vs H: L = Low melt index (low flow), good strength retention; H = High melt index (high flow), suitable for complex molds and large thin-walled parts.
LGF30 (30% Long Glass Fiber) – Most Commonly Used Grade: LGF30 is mainstream grade of PP-LGF, offering the best balance of strength, rigidity, toughness, and cost. It is preferred material for replacing steel with plastic in automotive structural components. SABIC Stamax series is benchmark product for global automotive LGF-PP.
LGF40 (40% Long Glass Fiber) – High Load Capacity: LGF40 is a high load capacity material with rigidity and strength approaching that of engineering plastics, used to replace metal in high-load-bearing structural components. However, its high glass fiber content makes processing more difficult and results in poorer surface quality.
II. Mechanical Property Characteristics and Yield-to-Trypance Ratio
Mechanical properties of PP-LGF show a regular variation with glass fiber content. Long glass fibers bring unique performance characteristics not found in short glass fibers.
Typical Performance Comparison of Different LGF Contents
Typical Performance Comparison of Different LGF Contents
| Properties | LGF20 | LGF30 | LGF40 | Testing Standards |
| Density | ~1.04 g/cm² | ~1.13 g/cm² | ~1.22 g/cm2 | ISO1183 |
| Tensile Strength | 80~95 MPa | 90~110 MPa | 110~130 MPa | ISO 527 |
| Tensile Modulus | 4000~5000MPa | 5500~77000Pa | 7000~8500MPa | ISO 527 |
| Elongation at Break | 3~5% | 2~4% | 2~3% | ISO 527 178 |
| Flexural Modulus | 3500~5000MPa | 5000~6500MPa | 7000~8000 MPa | ISO178 |
| Flexural Strength | 80~110 MPa | 110~140MPa | 150~180Pa | ISO178 |
| Notched Charpy Impact (23℃) | 15~20 kJ/m² | 20~30 kJ/m2 | 15~25 kJ/m2 | ISO179 |
| Notched Charpy Impact (-30℃) | 12~18 kJ/m² | 20~28 kJ/m2 | 12~20 kJ/m2 | ISO179 |
| Heat Deflection Temperature (0.45MPa) | 145~155℃ | 155~165℃ | 160~170℃ | ISO 75 |
| Heat Deflection Temperature (1.8MPa) | 120~140℃ | 145~160℃ | 155~165℃ | ISO 75 |
| Molding Shrinkage (Flow Direction) | 0.3~0.5% | 0.2~0.4% | 0.1~0.3% | ISO 294-4 |
Note: Above are typical ranges for materials of same grade. Specific values vary depending on fiber length retention, coupling agent type, and matrix type (homopolymer/copolymer). Impact strength of long glass fibers is very sensitive to fiber length.
Yield Strength Ratio Analysis
Yield strength ratio (yield strength / tensile strength) of PP-LGF has following characteristics: LGF20: High yield strength ratio (~0.85~0.9), close to brittle fracture. LGF30: Even higher yield strength ratio (~0.9~0.95), almost no obvious yield point. LGF40: Highest yield strength ratio (~0.95+), direct brittle fracture.
Engineering Conclusion: Although impact toughness of long glass fibers is much better than that of short glass fibers, static tensile testing still results in a brittle fracture mode (elongation at break is only 2~4%). "Toughness" of long glass fibers is mainly reflected in impact and dynamic loads, not in static tensile testing.
Unique Performance Advantages of Long Glass Fibers
Low Temperature Toughness: Impact strength of short glass fiber PP drops significantly at -30℃ (potentially by more than 50%), while low temperature impact strength of long glass fiber PP decreases very little or not at all—this is very important for northern regions and new energy vehicle battery packs. Fatigue Resistance: Fatigue life of long glass fibers is 2-3 times that of short glass fibers. Components subjected to repeated loads, such as seat frames and chassis parts, must use long glass fibers. Creep Resistance: Long glass fiber network structure effectively inhibits matrix creep, resulting in minimal deformation under long-term loads. This is particularly advantageous for high-temperature, long-term load-bearing components (such as engine components). Energy Absorption: During a collision, long glass fibers absorb energy through multiple mechanisms, including fiber pull-out, fiber breakage, and matrix cracking, achieving a much higher energy absorption efficiency than short glass fibers.
Molding process of PP-LGF is more complex than that of short glass fiber PP. Core challenge is maintaining fiber length and controlling anisotropy.
Key Process Parameters
Yield Strength Ratio Analysis
Yield strength ratio (yield strength / tensile strength) of PP-LGF has following characteristics: LGF20: High yield strength ratio (~0.85~0.9), close to brittle fracture. LGF30: Even higher yield strength ratio (~0.9~0.95), almost no obvious yield point. LGF40: Highest yield strength ratio (~0.95+), direct brittle fracture.
Engineering Conclusion: Although impact toughness of long glass fibers is much better than that of short glass fibers, static tensile testing still results in a brittle fracture mode (elongation at break is only 2~4%). "Toughness" of long glass fibers is mainly reflected in impact and dynamic loads, not in static tensile testing.
Unique Performance Advantages of Long Glass Fibers
Low Temperature Toughness: Impact strength of short glass fiber PP drops significantly at -30℃ (potentially by more than 50%), while low temperature impact strength of long glass fiber PP decreases very little or not at all—this is very important for northern regions and new energy vehicle battery packs. Fatigue Resistance: Fatigue life of long glass fibers is 2-3 times that of short glass fibers. Components subjected to repeated loads, such as seat frames and chassis parts, must use long glass fibers. Creep Resistance: Long glass fiber network structure effectively inhibits matrix creep, resulting in minimal deformation under long-term loads. This is particularly advantageous for high-temperature, long-term load-bearing components (such as engine components). Energy Absorption: During a collision, long glass fibers absorb energy through multiple mechanisms, including fiber pull-out, fiber breakage, and matrix cracking, achieving a much higher energy absorption efficiency than short glass fibers.
Molding process of PP-LGF is more complex than that of short glass fiber PP. Core challenge is maintaining fiber length and controlling anisotropy.
Key Process Parameters
| Parameters | Recommended Range | Description |
| Barrel Temperature | 220-260℃ | Segmented heating, 20-40℃ higher than ordinary PP |
| Mold Temperature | 60-100℃ | High mold temperature improves surface quality and reduces fiber floating |
| Injection Pressure | 80-150MPa | Long glass fiber materials have poor flowability and require higher pressure |
| Screw Speed | 30-80 rpm | Low speed reduces fiber breakage |
| Back Pressure | 3-10 MPa | Low back pressure reduces fiber shearing |
| Injection Speed | Medium-High Speed | Fast mold filling reduces fiber orientation time |
III. Application Overview
Core value of PP-LGF is its high-end structural components that "replace steel with plastic"—using plastic to replace metal load-bearing structural components, achieving significant weight reduction and cost reduction.
Automotive Applications
Automotive Applications
| Components | Common grades | Key Requirements | Alternative Materials | Weight Reduction Effect |
| Front-end module | LGF30 / LGF40 | High rigidity, high impact, integrated design, dimensional stability | Steel stamping and welding components | 30~40% |
| Seat frame/backrest | LGF30 / LGF40 | High strength, fatigue resistance, collision safety | Steel seat frame | 20~30% |
| Dashboard frame | LGF20 / LGF30 | High rigidity, low VOC, dimensional stability | Steel plate frame | 30~40% |
| Tailgate inner panel | LGF30 / LGF40 | High strength, high rigidity, dimensional stability, creep resistance | Steel tailgate | 25~35% |
| Battery tray/bracket | LGF30 / LGF40 | High rigidity, insulation, corrosion resistance, impact resistance | Aluminum/steel structure | 30~50% |
| Door module/door base plate | LGF20 / LGF30 | High rigidity, integrated function, low warpage | Steel plate + plastic | 25~35% |
| Engine underbody protection plate | LGF30 / LGF40 | Stone impact resistance, heat resistance, fatigue resistance | Metal skid plate | 40~50% |
| Engine hood | LGF30 / LGF40 | Heat resistance, vibration resistance, oil resistance | Metal cover | 30~40% |
| Step bracket | LGF30 / LGF40 | High strength, fatigue resistance, safety | Metal bracket | 30~40% |
Why use LGF30 for front-end module? Front-end module integrates more than 10 metal parts, including a heat sink, speaker, condenser, and bracket, all injection molded from PP-LGF30, resulting in a 30-40% weight reduction, fewer assembly steps, and significant cost reduction. It also offers corrosion resistance and high design freedom. High impact and fatigue resistance of long glass fiber ensures safety during collisions and long-term use.
New Energy Vehicle Battery Tray: Battery tray is a core structural component of new energy vehicles, requiring high rigidity, insulation, corrosion resistance, and bottom impact resistance. PP-LGF30/40, with its advantages of lightweight (30-50% lighter than aluminum), insulation, corrosion resistance, high molding freedom, is rapidly replacing aluminum and steel structures.
Home Appliance Applications
Home Appliance Applications
| Components | Common grades | Key requirements |
| Washing machine inner drum/tripod | LGF30 / LGF40 | High rigidity, water resistance, fatigue resistance, detergent resistance |
| Air conditioner fan/duct | LGF20 / LGF30 | High rigidity, low noise, heat resistance |
| Dishwasher components | LGF30 | Hot water resistance, detergent resistance, fatigue resistance |
Industrial and Other Applications
| Applications | Typical Products | Core Advantages |
| Power Tools | Drill Housings, Angle Grinder Housings | High Strength, Impact Resistance, Fatigue Resistance |
| Sports Equipment | Skiboards, Bicycle Components | Lightweight, High Strength |
| Building Materials | Door and Window Reinforcing Profiles, Pipes | High Strength, Corrosion Resistance |
| Logistics | Takeout Boxes, Pallets | High Load Capacity, Impact Resistance, Durability |
Typical Simulation Scenarios
| Simulation Types | Model Used | Results to Consider |
| Static Stiffness | Anisotropic Elastic-Plastic | Displacement, Stress Distribution |
| Modal/NVH | Orthotropic Elastic | Natural Frequency, Mode Shape |
| Collision/Impact | Elastic-Plastic + Asymptotic Damage | Energy Absorption, Penetration, Failure Mode |
| Creep (Long-Term Load) | Viscoelastic/Creep Model | Long-Term Deformation, Stress Relaxation |
| Vibration Fatigue | Elastic-Plastic + Fatigue Criterion | Fatigue Life, Safety Factor |
| Warpage Prediction | Thermo-Elastic-Plastic + Orientation | Warpage, Residual Stress |
| Stone Impact/Falling Hammer | Rate-Related Elastic-Plastic + Damage | Damage Range, Penetration |
Failure modes of PP-LGF are similar to those of short glass fiber PP, but it also has failure characteristics unique to long glass fiber.
Impact Fracture
Problem: Fracture under impact load. Although long glass fibers exhibit significantly better impact toughness than short glass fibers, they can still fail under high-energy impacts. Failure modes include fiber pull-out, fiber breakage, and matrix cracking.
Common scenarios: Collisions, stone impacts, drops, low-temperature impacts.
Solutions:
Impact Fracture
Problem: Fracture under impact load. Although long glass fibers exhibit significantly better impact toughness than short glass fibers, they can still fail under high-energy impacts. Failure modes include fiber pull-out, fiber breakage, and matrix cracking.
Common scenarios: Collisions, stone impacts, drops, low-temperature impacts.
Solutions:
| Direction | Specific Practices |
| Materials | Increase glass fiber content (from LGF20 to LGF30) |
| Materials | Select high-impact grade (toughened LGF) |
| Materials | Optimize fiber length retention (low-shear process) |
| Design | Enlarge corner radius to avoid sharp corners and notches |
| Design | Reinforce to increase rigidity and energy absorption capacity |
| Design | Avoid weld lines in high-stress areas |
| Process | Optimize process to maintain fiber length |
Fatigue Failure
Problem: Under repeated loading, the fiber-matrix interface debonds, fibers gradually break, and eventually fatigue failure occurs. Long glass fibers have 2-3 times better fatigue performance than short glass fibers, but fatigue failure still occurs under high loads and high frequencies.
Common scenarios: Seat vibration fatigue, chassis component road surface fatigue, fan blade rotation fatigue.
How to solve:
Problem: Under repeated loading, the fiber-matrix interface debonds, fibers gradually break, and eventually fatigue failure occurs. Long glass fibers have 2-3 times better fatigue performance than short glass fibers, but fatigue failure still occurs under high loads and high frequencies.
Common scenarios: Seat vibration fatigue, chassis component road surface fatigue, fan blade rotation fatigue.
How to solve:
| Direction | Specific Practices |
| Materials | Replace short glass fibers with long glass fibers (2-3 times longer fatigue life) |
| Materials | Increase glass fiber content |
| Materials | Surface treatment of glass fibers to improve interfacial bonding |
| Design | Reduce stress levels; increase corner radius |
| Design | Avoid weld lines in high-stress areas |
| Process | Optimize process to maintain fiber length |
Development Trends
Ultra-high content LGF (50%+): Higher strength and rigidity, replacing more metal structural components. Low warp LGF: Glass fiber + mineral composite, special fiber morphology, reducing anisotropy and warping. Low density, high rigidity LGF: Hollow glass microspheres, nanofillers, improving rigidity without increasing density. Flame retardant LGF: Halogen-free flame retardant LGF, used in battery packs, electronic appliances, and other structural components requiring flame retardancy. Low VOC / Low odor LGF: Meets environmental protection requirements for automotive interiors. Continuous glass fiber reinforced (CFRTP/UD tape): Thermoplastic composite material, higher strength, can replace metal load-bearing components. LGF microfoaming: Chemical/physical foaming, weight reduction of 15~25%, while improving sound insulation and warping. Recycled LGF: Improved quality of recycled materials, increased application in non-critical structural components. Online mixing LFT: Online mixing + injection molding integration, reducing costs and flexibly adjusting formulations
Ultra-high content LGF (50%+): Higher strength and rigidity, replacing more metal structural components. Low warp LGF: Glass fiber + mineral composite, special fiber morphology, reducing anisotropy and warping. Low density, high rigidity LGF: Hollow glass microspheres, nanofillers, improving rigidity without increasing density. Flame retardant LGF: Halogen-free flame retardant LGF, used in battery packs, electronic appliances, and other structural components requiring flame retardancy. Low VOC / Low odor LGF: Meets environmental protection requirements for automotive interiors. Continuous glass fiber reinforced (CFRTP/UD tape): Thermoplastic composite material, higher strength, can replace metal load-bearing components. LGF microfoaming: Chemical/physical foaming, weight reduction of 15~25%, while improving sound insulation and warping. Recycled LGF: Improved quality of recycled materials, increased application in non-critical structural components. Online mixing LFT: Online mixing + injection molding integration, reducing costs and flexibly adjusting formulations
Last article：Summary of hot runner structure design for injection molds
Next article：Return list
Recommended
Related
- Plastics Materials (Part 5): In-depth Analysis of PP-LGF10-21
- Summary of hot runner structure design for injection molds10-20
- Is your mass production yield stuck in 75%-85% range? Excluding materials and equipment, here are 710-20
- Introduction to die casting and post-processing technology10-19
- Design of a Two-Step Ejection Injection Mold for Inner Panel of a New Energy Vehicle Door10-19