How far apart are they at -20 °C in notched impact?

Answer: 9 kJ/m² for HDPE, 3.2 for homopolymer PP, 26 for copolymer PP to GB/T 1843. Homopolymer PP keeps 40% of room-temperature impact, so it has no margin below -20 °C.

Same envelope, how much heavier is the PE body?

Answer: The 4%–6% density gap makes a 48 L, 3 mm case 6.4 kg in HDPE against 5.9 kg in PP. Growing PP walls to 4 mm for stiffness ends 0.8 kg heavier.

Does switching resin in an existing mould work?

Answer: No. PP cavities are cut at 1.6% and HDPE at 2.2%, 2.5 mm over a 420 mm body, and vent depth moves from 0.08 mm to 0.12 mm.

Why do PP cases sag in a hot climate?

Answer: Creep in PP vs PE bodies accelerates above 40 °C, where 20 kg static for 24 h gives 3.0 mm. Stacked at 60 °C for 30 days, permanent set reaches 6 mm; ribs at 3× wall height hold it inside 3 mm.

Can copolymer PP replace PE at -30 °C?

Answer: With 0.5 mm more wall and no sharp corners. Copolymer PP brittles at -25 °C, so a -30 °C spec leaves 5 K, and a 5 kg/1 m drop gives a 12 mm crack rather than a split.

Do PP vs PE bodies accept the same regrind ratio?

Answer: No. HDPE at 30% regrind loses 18% of -20 °C impact with melt index drifting ±12%, fine for shells. PP loses 15% but drifts from 1.6% to 1.9% shrinkage, so load-bearing parts stay at 10%.

PP vs PE Bodies: Cold Toughness vs Stiffness

Quick answer: PP vs PE bodies split on one temperature line: HDPE keeps chain mobility to -120 °C, homopolymer PP freezes near 0 °C, and -20 °C costs PP 3.2 kJ/m². Above that line PP wins on stiffness at 1.3–1.6 GPa against 0.9–1.1 GPa, and mass, shrinkage and oven temperature follow the choice.

Where the two materials part
Stiffness: flexural modulus and lid sag
Cold: drop hammer and brittleness
Process: oven temperature and warp
Cost and a three-tier screen
FAQ

1. Where PP vs PE bodies diverge

PP vs PE bodies splits first on crystallinity: HDPE reaches 70%–90% and 0.94–0.96 g/cm³, homopolymer PP 50%–60% and 0.90–0.91 g/cm³. On a 48 L case with 3 mm walls that gap is 6.4 kg against 5.9 kg, or 7.8%.

The glass transition is the second line. HDPE sits near -120 °C, so its segments still move at -40 °C and absorb impact by yielding. Homopolymer PP sits near 0 °C, so by -20 °C it has only crazing and cracking, and notched impact falls from 8 to 3.2 kJ/m².

Copolymer PP is the third route: 5%–8% ethylene pushes the rubber phase below -50 °C and holds 26 kJ/m² at -20 °C, costing flexural modulus, 1.1–1.4 GPa against 1.6 GPa.

Property	HDPE	PP homopolymer	PP copolymer
Density g/cm³	0.94–0.96	0.90–0.91	0.90–0.91
Glass transition °C	-120	0	rubber -50
Flexural modulus GPa	0.9–1.1	1.3–1.6	1.1–1.4
Impact 23 °C kJ/m²	12, no break	8	45
Impact -20 °C kJ/m²	9	3.2	26
Shrinkage %	1.5–3.0	1.2–2.0	1.3–2.1

Impact values follow GB/T 1843 on 1eA bars and do not convert to ASTM D256 J/m; read the temperature row first.

2. Stiffness: flexural modulus and lid sag

Flexural modulus to GB/T 9341 sets sag. A 600 mm × 400 mm cover with 3 mm walls, carrying 60 kg spread evenly at 25 °C, sags 3.8 mm in HDPE and 2.6 mm in PP.

PP vs PE bodies on a steel shelf, lid ajar, white handles, two front latches, leather grain and light scuffing

Thicker walls buy stiffness back: 4 mm takes HDPE to 1.6 mm but adds 1.4 kg and 13 CNY, while PP reaches 1.1 mm for 1.3 kg more.

Long loads are a creep question. At 40 °C with 20 kg for 24 h, HDPE deflects 4.6 mm and PP 3.0 mm; two hours after unloading HDPE recovers 62% and PP 78%.

Ribs behave differently in PP vs PE bodies. HDPE ribs at 3× wall height and 0.6× wall thickness recover about 35% of stiffness; PP is stiff enough that dense ribs mainly leave 0.15 mm sink marks at the roots.

3. Cold: drop hammer and brittleness

Cold performance is a drop-hammer question. A 5 kg head from 1 m onto a corner after 4 h at -40 °C leaves HDPE dented 9 mm with no penetration and a whitened edge; homopolymer PP splits in two with no stress whitening; copolymer PP cracks 12 mm. Brittleness temperature traces that line: below -70 °C for HDPE, -5 °C for homopolymer PP, -25 °C for copolymer PP. A -30 °C spec leaves homopolymer PP no margin, copolymer PP 5 K. PP vs PE bodies also fail in different places. Corners at R8 carry a stress concentration near 2.4 and latch post roots near 3.1; HDPE yields locally at -40 °C, while homopolymer PP cracks and runs 40 mm along a weld line.

4. Process: oven temperature and warp

Oven temperature follows melting point: homopolymer PP melts at 160–166 °C and runs at 230–260 °C for 22–28 min, HDPE at 260–290 °C for 18–22 min. PP sinters more slowly, so cycles run 5 min longer and output drops 12%.

PP vs PE bodies from above: off-white shell, rounded corners, shallow lid recess, flush latch bosses, no flow lines

Shrinkage sets the cavity in PP vs PE bodies: 1.2%–2.0% for PP against 1.5%–3.0% for HDPE, so a 420 mm body is cut at 426.7 mm and 429.2 mm. Annealing at 80 °C for 2 h recovers 0.3% in HDPE and 0.1% in PP.

Warp runs in different directions. PP drifts to 1.5 mm flatness over 500 mm, forcing a 2 mm joint allowance; balanced cooling within 8 °C pulls HDPE back to 0.8 mm.

Powder follows the resin: PP needs 35 mesh and a 4 mm mould, HDPE a 3 mm mould and 15% less tooling cost.

5. Cost and a three-tier screen

Material runs 9.2 CNY/kg for HDPE and 10.8 CNY/kg for copolymer PP. The 6.4 kg HDPE body carries 59 CNY of compound against 64 CNY for the 5.9 kg PP body, and 5 min more in the mould adds 7 CNY, so landed cost differs by 12 CNY.

Item	HDPE body	PP copolymer body
Case mass kg	6.4	5.9
Compound cost CNY	59	64
Mould time min	20	25
−40 °C drop	dent, no split	12 mm crack

Screen PP vs PE bodies on minimum service temperature rather than on resin names.

Minimum service temp	Resin	Wall mm	Governing check
Below -30 °C	HDPE	3.0–3.5	drop and brittleness
-30 to -10 °C	PP copolymer, 5%–8% ethylene	2.5–3.0	impact versus modulus
Room temperature	PP homo or copolymer	2.2–2.8	lid sag and finish

Two items get missed: a cracked HDPE body hot-gas welds to 70% of parent strength, while a split PP shell cannot be repaired; at 30% regrind, -20 °C impact drops 18% in HDPE and 15% in PP.

Conclusion

The choice between PP vs PE bodies comes down to the lowest temperature the case will meet, not to which polymer is better. Below -30 °C, HDPE buys margin through ductile tearing. From -30 to -10 °C, copolymer PP holds 26 kJ/m² with most of its stiffness. At room temperature, homopolymer PP wins on 1.6 GPa and 2.6 mm sag. After that, three numbers decide: 7.8% of mass, 2.5 mm of cavity, 7 CNY of cycle time. JUNZHIJIA quotes wall, rib height and grade as one package so the drop result can be checked.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.