渔船浮球用什么改性PP，先要划清边界：大规格海上浮球主流是 PE 与 EPS 路线，改性PP 的位置在中小规格外壳、水产养殖箱与船用非承力件上。这篇把海水工况六维、五条路线分工、八项判据与验证顺序摆清楚，并说明哪四个条件同时出现时，这个件不该用改性PP。
有个做养殖设施的技术员发来一张照片：养殖箱用了两季，边上开始发脆，抬起来一磕就裂。他问，是不是料的问题。
另一个问的是浮球：泡了一年，表面全是麻点，捞上来一称，比新的重。
这两件事，一件是低温脆裂，一件是海水老化与吸水，正好是"渔船浮球、水产养殖箱与船用非承力件"上最常见的两个现场。
先把边界讲清楚，这一篇才好往下走。
核实过一遍公开资料，结论要照实说：在海上养殖这一块，浮球的主流做法不是改性PP。 大规格（直径 50 cm 以上）海上养殖浮球与浮筒，公开的地方设施渔业技术要求里写的是高密度聚乙烯（HDPE）原生料，有的还明确要求"浮球不使用填充物"；市售养殖浮球里更常见的是 PE 滚塑外壳 + EPS 泡沫实心填充——好处是外壳破了、内部仍保留浮力。拖网渔具用的硬质球形浮子，行业标准 SC/T 4050.2-2019 的适用主体是 ABS 塑料浮子，"其他类型浮子可参照执行"；泡沫浮球另有 SC/T 5009-1995。
那改性PP 的位置在哪？ 公开产品资料里能看到 PP 球体 + EPS 泡沫填充的拖网浮球，规格偏中小；更实在的两块是水产养殖箱、桶、槽（注塑与滚塑），以及船上的非承力注塑件——舱盖、格栅、箱体、护板、支架这一类。下面按工况、路线、判据、验证四层往下拆。
一、工况六维拆解：浮球与养殖箱，比内陆户外件多两件事
结论放在前面：海水件的工况不是"户外件加点盐"，是盐雾与浸泡叠在温度、载荷之上。六个数报齐，方向基本就出来了。
| 维度 | 浮球 / 养殖箱 / 船用件的实际工况 | 对材料的要求 |
|---|
| 温度 | 夏季甲板暴晒，表面可到 60-70℃；冬季近海夜间降到 0℃ 以下，冷库与冷链周转按 −18℃ 计 | PP 公开使用温度范围 −30~140℃，脆化温度约 −35℃（B 级）；低温冲击是硬线 |
| 载荷 | 1 m³ 养殖水体约 1 t；箱体常按 2-3 层堆叠；吊装是点载荷；浮球类按 2 m 高度跌落不破碎 考核（SC/T 4050.2-2019） | 弯曲模量与低温冲击一起看：刚性不够鼓肚，韧性不够磕裂 |
| 介质 | 海水盐雾（5% NaCl、35±2℃、pH 6.5-7.2，GB/T 10125-2021）；养殖水体里的残饵、粪便、氨氮；清洗剂与油污 | 耐候、耐盐雾、耐化学三条不能只做一条 |
| 寿命 | 渔船件常见换件周期 3-5 年；养殖设施按季或按年周转；海上养殖塑料设施公开口径 5-8 年 | 老化后的力学保留率，比初始指标更值得当门限 |
| 外观 | 海水件多为警示色（红、橙、黄），褪色本身等于功能下降；麻点与粉化是早期信号 | 色差与失光要一并进入老化考核 |
| 合规 | 接触养殖水体时的迁移与重金属；浮球类另有浮力与耐压考核 | 迁移可参照 GB 4806.7-2023 的口径做考察并留档，最终以客户验收约定为准 |
文字版结论：六维里温度与介质是叠加关系——白天暴晒推高温度，夜里结露、盐分留在表面，第二天再晒。内陆户外件只需考虑"晒"，海水件要考虑"晒 + 盐 + 湿"的循环，这就是耐候配方不能直接照抄的原因。
一个内行细节：PP 树脂本体吸水性极低，23℃/24h 约 0.01%（B 级）。所以"泡一年变重"多半不是树脂吸水，而是三处——填充体系吸潮、发泡芯材吸水、结构缝隙进水。判据要落在"整件质量变化 + 浮力变化"上。
二、材料路线对比：浮球材料、养殖箱材料、船用塑料件各占哪一段
结论：这个领域的选型不是"PP 对 PE"的单选题，而是五条路线各占一段。
| 路线 | 典型形态 | 拿到什么 | 代价 / 边界 |
|---|
| 共聚 PP + 耐候体系 | 注塑养殖箱、槽、船用格栅与护板 | 刚性、耐热、耐化学；尺寸稳定好调 | 低温韧性要靠增韧补；长期浸海水仍需复合老化考核 |
| 抗冲共聚 PP + 增韧 | 需要抗磕碰与低温的箱体、承水件 | 低温冲击与抗跌落实测值上得来 | 加韧会换掉流动性；厚壁件要同时顾缩痕 |
| PE（滚塑 / 厚壁吹塑） | 大规格海上浮球、浮筒、大型槽体 | 厚壁一次成型、抗冲击好；是浮球类主流材质 | 刚性与耐热低于 PP；滚塑周期长 |
| EPS 泡沫（常配 PE 外壳） | 养殖浮球、警示浮球 | 密度低、闭孔吸水率低；外壳破损后内部仍留浮力 | 泡沫本体强度低，必须靠外壳保护 |
| PVC 泡沫 / 玻璃钢 | 泡沫浮球、平台与走道等结构件 | 泡沫浮球有专门标准（SC/T 5009-1995）；玻璃钢强度高 | PVC 的环保与回收受关注；玻璃钢不属于热塑成型 |
不做"谁更好"的结论。分工的界线是三条：是不是长期浸海水、是不是承力、规格多大。 三条里中两条，方向基本就定了——这也是为什么客户拿着"我要做浮球"来问时，第一句要问的是规格和壁厚，不是牌号。
敢否定一个常见做法：把内陆户外件的耐候配方直接套到海水件上，是这个领域最常见的错。海水环境的老化不是单纯的 UV 老化——盐雾、湿热、温度循环会叠加，助剂被消耗得更快。 公开研究里有一个值得记住的对照：PP 样品在天然海水中浸泡满 12 个月，重量损失只有 0.65%（同期 LDPE 1.9%、HDPE 1.6%）；而另一组被反复引用的数据里，PE 与 PP 海水暴露一年后的拉伸性能分别下降约 12% 与 26%（Pegram & Andrady 1989，经 Artham 等 2009 综述引用）。外观几乎不变、重量几乎不增，力学却掉了大半——这就是海水件"看着好好的、一受力就裂"的原因。
三、★ 选型判据表：八项指标，每项都带验证方法与口径
注意第三列——卡住的往往不是"看哪个指标"，而是"拿什么测、测到多少算过"。
| 指标 | 门限值（典型） | 验证方法 / 标准 | 常见失效 | 通行解法 |
|---|
| 海水 / 盐雾老化后的力学保留率 | 拉伸保留率 ≥80%、弯曲保留率 ≥75%、冲击功变化在 ±10 J 内（检测机构公开技术文口径，B 级）；时长按 24 / 48 / 96 h 或客户约定 | GB/T 10125-2021《人造气氛腐蚀试验 盐雾试验》（5% NaCl、35±2℃、pH 6.5-7.2）；老化后按 GB/T 1040.2、GB/T 9341、GB/T 1043.1 复测保留率 | 表面麻点、发脆、冲击值断崖 | 耐候体系 + 抗氧体系复配，必要时补足炭黑 |
| 低温冲击（悬臂梁缺口） | −20℃ ≥93 J/m | 悬臂梁缺口冲击（ISO 180 / ASTM D256 口径，台化 K8003 物性表，B 级）；试样放置 16-24 h 后测 | 冬季与冷库周转时的脆裂 | 抗冲共聚基材 + 增韧体系加量 |
| 弯曲模量 | 900-1500 MPa | GB/T 9341（燕山 K4912、中海壳牌 EP300M-Z 物性表口径，A 级） | 装满水后鼓肚、堆叠压塌 | 共聚 / 均聚选档 + 薄壁加筋 |
| 吸水与增重 | 树脂本体 23℃/24h 约 0.01%（B 级）；发泡芯体系另按浸没 96 h 浮力法测，整件门限由客户验收约定 | GB/T 1034-2008《塑料 吸水性的测定》（方法 1：23℃/24h；方法 2：沸水 30 min）；发泡芯按 GB/T 8810-2005《硬质泡沫塑料吸水率的测定》（浸没水下 50 mm、96 h，浮力法） | 浮力下降、整件增重、箱体吸味 | 提高闭孔率、控制填充吸潮、结构上留排水 |
| 浮力与耐压（浮球类） | 浮力按规格：Ø240 mm 级 ≥6 N 起，Ø400 mm 级到 30 N；耐压按 150 / 200 / 300 m 水深分三级（1500-3000 kPa）；破碎压力为工作压力的 1.33-2 倍 | SC/T 4050.2-2019（适用主体为硬质球形 ABS 浮子，其他类型浮子可参照执行）+ SC/T 5002-2009《塑料浮子试验方法 硬质球形》 | 破口进水、耐压不足被压扁 | 中空结构 + 壁厚设计；或走填充式外壳路线 |
| 炭黑含量与抗 UV 强度保持率 | 炭黑含量 ≥2.0%；抗 UV 强度保持率 ≥90% | JT/T 1432.1-2022（土工格栅口径；海水件可参照其"炭黑 + 强度保持"两项） | 户外暴晒后粉化、断裂伸长骤降 | 足量炭黑 + 光稳定剂复配 |
| 紫外老化（荧光紫外灯） | 色差与力学保留按客户约定；行业通行做法是 500-1000 h | GB/T 16422.3-2022《塑料 实验室光源暴露试验方法 第 3 部分：荧光紫外灯》 | 褪色、失光、表层粉化 | 光稳定剂体系 + 耐候等级色母 |
| 耐油污与耐清洗剂后的外观与性能保留 | 浸泡 / 擦拭后无失光与龟裂，力学保留率由客户约定 | 按客户提供的介质清单做浸泡后再测力学（国家层面无专门门限，口径以客户约定为准） | 表面发黏、龟裂、标识脱落 | 选耐化学档基材；避免件上留应力集中 |
文字版结论：八项里两项最该先看——盐雾老化后的力学保留率（决定用不用得住）与 −20℃ 低温冲击（决定冬天破不破）。还要提醒：这个领域没有一部"水产养殖用塑料件"的通用强制产品标准，浮球类的 SC/T 4050.2-2019 与 SC/T 5002-2009 适用主体写的是 ABS 硬质球形浮子；养殖箱与船用非承力件更多是行业通行验收口径 + 客户约定。判据表的作用是把"要测什么、怎么测"提前写进验收文件。
四、常见失效与根因：四个现象，四条根因
失效一：箱体边角发脆、一磕就裂。 根因多数是低温韧性不足，或者壁厚在转角处减薄过快造成应力集中。先查壁厚与圆角，再查料；顺序反了会白换几轮。
失效二：表面麻点、粉化、褪色。 先看是不是 UV 与盐雾叠加（盐雾按 GB/T 10125-2021，5% NaCl、35±2℃），再看炭黑与光稳定剂加量是否足。只做氙灯或紫外、不做盐雾，是海水件最常见的漏项。
失效三：泡满一季之后整件变重、浮力下降。 根因通常不在树脂——PP 本体 23℃/24h 吸水率约 0.01%——而在填充吸潮、芯材吸水与结构缝隙进水。查的顺序是：先看结构有没有存水的腔与缝，再看芯材闭孔率，最后才是树脂。
失效四：装满水放两天鼓肚。 这是弯曲模量与蠕变的事，不是"料软了"。弯曲模量门限按 900-1500 MPa 档定（A 级），低于这个档又做薄壁，鼓肚是必然。
还有一条容易被忽略的：只看常温冲击选材、忽略低温脆化，是养殖箱冬季破损的主因。 常温下测得漂亮的冲击值，在 −20℃ 可能只剩一个零头。低温这一项不能靠"常温数据好"去推，必须按 −20℃ 实测。
五、验证顺序：耐海水老化的件，先验什么后验什么
结论：顺序是外观 → 吸水与密度 → 盐雾老化后力学 → 低温冲击 → 满水承重与吊装 → 整箱跌落。跳一步，代价会在最后集中爆出来。
`
① 外观与色差 色板比对、色差与失光
↓ 不过就退回配方与色母
② 吸水率与密度 23℃/24h、沸水 30 min；发泡芯按浸没 96 h 浮力法
↓ 不过就退回填充体系与芯材
③ 盐雾 / 湿热老化后力学保留 GB/T 10125-2021，再测拉伸、弯曲、冲击保留率
↓ 这一关不过，后面全部不用做
④ 低温冲击 −20℃ 悬臂梁缺口冲击，试样放置 16-24 h 后测
↓ 不过就退回增韧体系与基材档位
⑤ 满水承重与吊装 按实际装载量与吊点做静载与吊装
↓ 不过就退回结构与壁厚设计
⑥ 整箱跌落实测 按客户实际周转高度做
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最常见的错误是跳过 ① 和 ② 直接进 ③——用一件已经吸过水、已经轻微变色的样件去评判耐老化能力，测出来的数没有代表性。
文字版结论：盐雾后力学那一关必须排在承重与跌落之前——它最可能一票否决；过了它再做结构侧的事，才不会白花试模费。
六、反向诚实：这四个条件出现，浮球与船用塑料件就不该用改性PP
前面讲"怎么做"，这里讲"什么时候别做"。这一段对选型判断的价值最高。
| 出现的情况 | 为什么改性PP不合适 | 该往哪走 |
|---|
| 结构承力件，且要求船级社（CC）认证 | 改性PP 不在船级社材料体系的常规清单里，认证路径对不上 | 按船级社规范选材，走金属或玻璃钢 |
| 大规格海上浮筒，长期浸海水且反复受浪冲击 | 主流材质与公开的地方设施渔业技术要求都指向 HDPE；厚壁滚塑 / 吹塑的成型方式更适配 | PE 滚塑或厚壁吹塑 |
| 拖网浮子这类要承受水压、反复冲击的浮动件 | SC/T 4050.2-2019 的适用主体是 ABS 硬质球形浮子；PP 参照执行时，耐压与抗冲击要靠结构和壁厚硬扛 | ABS 硬质球形浮子，或 EPS 填充 + 外壳路线 |
| 要求金属级强度与长期耐候 | PP 的模量与蠕变是结构性的，靠改性只能缓解 | 金属件或玻璃钢 |
规律一致：凡是要"承力 + 认证 + 长期浸海水"三条同时出现，这个件就不该用改性PP。 遇到这种需求，先把这条讲清楚，再谈有没有折中空间——硬接下来的单子，最后都要用返工还回去。
七、换料要动什么：水产养殖箱件的一张先看再动清单
客户决定试改性PP之后，真正的顾虑往往不是性能，是"我现在的模具和工艺要不要改"。
| 要动的项 | 需要确认什么 | 不做会怎样 |
|---|
| 模具收缩率 | PP 的成型收缩率公开口径为 1%-2.5%，与 PE（1.5%-3.6%）不同；长件与大平面尤其敏感 | 尺寸超差、箱盖合不严、装配对不上 |
| 浇口与排气 | 养殖箱多为大件厚壁或带加强筋结构，流程长、排气点多 | 短射、困气烧焦、熔接线位置变化 |
| 料温与模温 | 耐候体系与增韧体系的工艺窗口不同 | 表面麻点、熔接线强度不足 |
| 干燥 | 填充体系与发泡芯材对水分敏感 | 银丝、气泡、局部发脆 |
| 保压与脱模 | 厚壁件收缩不均 | 翘曲、缩痕、顶白 |
| 色差 | 警示色件必须先确认色板与耐候等级 | 户外几个月褪成两批颜色 |
| 验证顺序 | 外观 → 吸水 → 盐雾后力学 → 低温冲击 → 承重吊装 → 跌落 | 风险全部压到最后一步集中爆发 |
文字版结论：养殖箱的换料风险集中在大件厚壁的收缩不均——翘曲与缩痕最常见，而且常被误判成"料缩了"。收缩率本身是设计输入，模具按哪个数开的，换料时就要按哪个数核对。 带筋箱体还要看筋位——筋根收缩慢，缩痕从那里出来。
八、一页纸汇报表（可以直接贴进 PPT）
| 场景 | 推荐路线 | 关键指标 | 验证标准 | 需先确认的条件 |
|---|
| 水产养殖箱 / 槽（注塑） | 共聚 PP + 耐候体系 | 弯曲模量 900-1500 MPa；老化后力学保留率 | GB/T 9341；盐雾按 GB/T 10125-2021 | 装载量与堆叠层数、最低使用温度 |
| 需要抗磕碰的箱体与承水件 | 抗冲共聚 PP + 增韧 | −20℃ 悬臂梁缺口冲击 ≥93 J/m | ISO 180 / ASTM D256；试样放置 16-24 h | 冬季周转温度、壁厚与圆角 |
| 船用非承力注塑件（格栅、护板、箱体） | 共聚 PP + 耐候 + 抗氧体系 | 老化后力学保留率；炭黑含量 ≥2.0% | GB/T 10125-2021；JT/T 1432.1-2022（参照炭黑与强度保持两项） | 是否长期浸水、有无油污与清洗剂 |
| 中小规格注塑浮球外壳 | 共聚 PP（中空结构） | 落体不破碎、密封与吸水量 | 参照 SC/T 4050.2-2019 的浮力与抗冲击考核口径 | 客户是否允许走 PE 或 EPS 填充路线 |
| 大规格海上浮球 / 浮筒 | 不推荐改性PP | — | — | 见第六节反向诚实段 |
文字版结论：这张表的作用是让技术员能把结论直接往上报，不必重新组织语言。判断标准只有一条——客户拿这张表，能不能在一次会议里把材料方向定下来。
九、这个件上最容易出问题的，往往不是料
公开的渔业技术要求里，浮球与踏板这类件的材料写得很具体：HDPE 原生料、不使用填充物、直径不小于 500 mm、长度不小于 900 mm、最小壁厚不小于 3 mm；SC/T 4050.2-2019 则把浮力门限、耐压分级与 2 m 跌落不破碎写成硬指标。共同点是：把"结构 + 壁厚 + 密封"放在材料之前。
养殖箱与船用非承力件的判据更靠近材料本身：弯曲模量落在 900-1500 MPa 档，低温冲击按 −20℃ 看，老化后要求力学保留。行业通行的做法是把这三件事一起定——基材档位、增韧与耐候体系、填充比例。三者的配平关系才是真正的技术难点，单看任何一项都没意义。
关键不在"谁的料更好"，在基材档位、增韧体系、耐候体系、结构与壁厚四件事能不能同时对得上。
宁波市科隆新材料有限公司在这个方向上常供的是改性聚丙烯（PP）粒子里的共聚与抗冲共聚方向，按件的使用温度、是否长期浸水、以及壁厚分布给到对应的基材档位与耐候、增韧体系，主要用来解决上面说的"低温磕裂与老化后力学掉得快"这两件事；配方按件的工况调，可以配合做小样比对与试模，件级客户多品种小批量的需求也能接。
常见问答
问：浮球到底能不能用 PP？
答：分规格和路线。公开资料里有 PP 球体 + EPS 填充的拖网浮球，规格偏中小、靠泡沫提供浮力；大规格海上浮球与浮筒，公开的渔业技术要求写的是 HDPE 原生料。PP 能用在中空结构的中小规格外壳上，但破口就进水；走泡沫填充路线，外壳破了内部仍留浮力。
问：养殖箱的料，是不是越韧越好？
答：不是。韧性与刚性在这是对拉的——为了低温不裂加增韧剂，弯曲模量会跟着下来，装满水容易鼓肚。正确做法是先定弯曲模量的档位（对应装载量与堆叠层数），再用增韧体系把低温冲击补到门限以上。
问：件只在内河用，还要做盐雾吗？
答：接触海水就要做。GB/T 10125-2021 的中性盐雾是 5% NaCl、35±2℃、pH 6.5-7.2，时长按 24 / 48 / 96 h 或客户约定。只做紫外、不做盐雾，是海水件最常见的漏项，漏掉的恰恰是助剂被消耗最快的那一条。
| 工况 | 关键判据 | 科隆常规供应 |
|---|
| 养殖箱 / 槽（注塑） | 弯曲模量 900-1500 MPa；老化后力学保留率 | 共聚 PP + 耐候体系方向 |
| 抗磕碰箱体与承水件 | −20℃ 悬臂梁缺口冲击 | 抗冲共聚 PP + 增韧方向 |
| 船用非承力件 | 盐雾后力学保留率；炭黑含量 | 共聚 PP + 耐候抗氧体系方向 |
想提醒一句：海水件出问题，最常见的错法是先换料。发脆、鼓肚、褪色、变重——每一条的原因都不止一个。先定位，再换料；顺序反了，往往换了几轮还在原地。
十、最后说三句
第一，先问这个件是不是"长期浸海水 + 承力"。 两条都占，改性PP 通常不是第一选择；只占一条，才有得谈。
第二，海水件的门限要落在"老化后"三个字上。 初始指标好看不等于用得住；盐雾与湿热之后还剩多少，才是真实寿命。
第三，验证顺序比验证项更重要。 外观 → 吸水 → 盐雾后力学 → 低温冲击 → 承重吊装 → 跌落，盐雾后力学那一关必须放在承重与跌落之前。
下一篇换一个件，继续按工况、路线、判据、验证四层往下拆。
关于我们
报价之前先聊三件事：这个件用在哪儿、要求哪几条、哪一条可以掉下来。
尤其第三件。改性 PP 的指标之间不是加法，是对拉——阻燃和增韧对拉，高流动和抗冲对拉，玻纤和尺寸稳定对拉。不排个先后，价格报不准，方案也稳不住。
宁波市科隆新材料有限公司，自产改性聚丙烯（PP）造粒，覆盖均聚 / 无规共聚 / 抗冲共聚三档基材，以及填充、玻纤增强、增韧、阻燃、低气味低 VOC、耐候、免喷涂耐划伤等改性方向；兼营各大石化厂 PP 树脂、副牌料与大包料。
What type of modified PP is used for fishing boat buoys? First, the boundaries need to be clarified: for large offshore buoys, the mainstream materials are PE and EPS, while modified PP is used for medium and small-sized casings, aquaculture boxes, and non-load-bearing parts on boats. This article clearly lays out six seawater working conditions, the division of five material routes, eight evaluation criteria, and the sequence of verification, and explains under which four conditions this component should not use modified PP.
A technician who works with breeding facilities sent a photo: the breeding box has been used for two seasons, and the edges are starting to become brittle, cracking at the slightest knock when lifted. He asked if it was a problem with the material.
Another one asked about the float ball: After soaking for a year, the surface is covered with pimples. When taken out and weighed, it's heavier than a new one.
These two issues, one being low-temperature brittleness and the other being seawater aging and water absorption, happen to be the two most common occurrences on 'fishing boat buoys, aquaculture boxes, and non-structural boat components'.
Let's clarify the boundaries first, so that we can proceed with this piece.
After verifying publicly available information, the conclusion must be stated truthfully: in the field of offshore aquaculture, the mainstream approach for buoys is not modified PP. Large-sized (diameter over 50 cm) offshore aquaculture buoys and floats, according to publicly available technical requirements for local aquaculture facilities, are made from virgin high-density polyethylene (HDPE), and some even explicitly require that 'buoys do not use fillers'; commercially available aquaculture buoys more commonly have a PE rotomolded shell with EPS foam solid filling—the advantage being that if the shell breaks, the interior still retains buoyancy. For trawl fishing hard spherical floats, the industry standard SC/T 4050.2-2019 applies primarily to ABS plastic floats, with 'other types of floats to refer to for implementation'; foam buoys are covered by a separate standard, SC/T 5009-1995.
So where is the modified PP located? In publicly available product information, you can see trawl floats made of PP spheres filled with EPS foam, with specifications leaning towards small to medium sizes; more tangible examples are aquaculture boxes, barrels, and troughs (injection molding and rotational molding), as well as non-load-bearing injection-molded parts on boats — things like hatch covers, grates, boxes, guards, and brackets. Below, we break it down into four layers according to working conditions, process, criteria, and validation.
1. Six-Dimensional Analysis of Working Conditions: Float Ball and Breeding Box, Two More Matters Than Inland Outdoor Components
Conclusion first: The operating conditions of seawater components are not 'outdoor components with some added salt'; they are salt spray and immersion superimposed on temperature and load. Once all six numbers are reported, the general direction basically emerges.
| Dimension | Actual working conditions of float balls / aquaculture tanks / marine parts | Requirements for the materials |
|---|
| Temperature | In summer, the deck can be exposed to the sun, with surface temperatures reaching 60-70°C; in winter, night temperatures near the sea can drop below 0°C, and cold storage and cold chain turnover are calculated at -18°C. | PP has a public usage temperature range of −30~140℃, with a brittle temperature of about −35℃ (Grade B); low-temperature impact is hard line |
| Load | 1 m³ of aquaculture water body weighs about 1 t; boxes are usually stacked 2-3 layers high; lifting is point load; floating ball types are tested for dropping from a height of 2 m without breaking (SC/T 4050.2-2019) | Looking at bending modulus together with low-temperature impact: if the stiffness is insufficient, it bulges; if the toughness is insufficient, it cracks. |
| Medium | Seawater salt spray (5% NaCl, 35±2℃, pH 6.5-7.2, GB/T 10125-2021); leftover feed, feces, and ammonia nitrogen in aquaculture water; cleaning agents and oil stains | Weather resistance, salt spray resistance, and chemical resistance cannot be addressed individually. |
| Lifespan | Fishing boat parts commonly have a replacement cycle of 3-5 years; aquaculture facilities are rotated seasonally or annually; offshore aquaculture plastic facilities have an open cycle of 5-8 years | The mechanical retention rate after aging is more worthy of being used as the threshold than the initial index. |
| Appearance | Seawater components are mostly warning colors (red, orange, yellow), and fading itself equals a decline in functionality; speckling and chalking are early signals. | Color difference and loss of gloss should both be included in the aging assessment |
| Compliance | Migration and heavy metals when in contact with aquaculture water; floating balls also have buoyancy and pressure resistance assessments | Migration can be examined and documented with reference to the caliber of GB 4806.7-2023, and the final standard shall be subject to the customer's acceptance agreement. |
Text version conclusion: In six dimensions, temperature and medium are superimposed—daytime sun exposure raises the temperature, at night condensation occurs and salt remains on the surface, and it is then exposed to the sun again the next day. For inland outdoor components, only 'sun exposure' needs to be considered, while for marine components, the 'sun-salt-humidity' cycle must be considered. This is why weather-resistant formulations cannot be directly copied.
An insider detail: The PP resin itself has very low water absorption, about 0.01% at 23°C/24h (Grade B). So the 'becomes heavier after a year' is mostly not due to the resin absorbing water, but from three areas — moisture absorption by the filler system, water absorption by the foam core material, and water ingress into structural gaps. The criteria should be based on 'overall weight change and buoyancy change'.
2. Comparison of material routes: Which segment is occupied by float ball materials, aquaculture box materials, and marine plastic parts
Conclusion: Choosing in this field is not a 'PP versus PE' multiple-choice question, but rather five routes each occupying a segment.
| Route | Typical form | Get what | Cost / Boundary |
|---|
| Copolymer PP Weather-Resistant System | Injection molded breeding tanks, troughs, ship gratings, and protective plates | Rigid, heat-resistant, chemically resistant; good dimensional stability and easy to adjust | Low-temperature toughness needs to be improved through toughening; long-term immersion in seawater still requires composite aging assessment. |
| Impact Copolymer PP Toughened | Enclosures and water-bearing parts that need to be impact-resistant and low-temperature resistant | The measured values of low-temperature impact and drop resistance are acceptable | Toughening will change the fluidity; thick-walled parts also need to take sink marks into account |
| PE (rotational molding / thick-wall blow molding) | Large-sized offshore buoys, floats, and large tanks | Thick-walled one-time molding, good impact resistance; it is the mainstream material for floating balls. | Rigidity and heat resistance are lower than PP; long rotational molding cycle |
| EPS foam (commonly paired with a PE outer shell) | Breeding buoys, warning buoys | Low density, low closed-cell water absorption; retains buoyancy even after the outer shell is damaged | The foam itself has low strength and must rely on the shell for protection. |
| PVC foam / fiberglass | Foam buoys, platforms, and walkways and other structural components | Foam float balls have specific standards (SC/T 5009-1995); fiberglass has high strength | The environmental protection and recycling of PVC are receiving attention; fiberglass is not thermoplastically molded. |
Do not draw a conclusion about 'which is better.' The division of labor is based on three boundaries: whether it is submerged in seawater for a long time, whether it bears load, and the size specifications. If two out of the three criteria are met, the direction is basically determined — this is also why when a customer asks 'I want to make a floating ball,' the first question asked is about the specifications and wall thickness, not the grade.
Dare to challenge a common practice: directly applying the weather-resistant formula for inland outdoor components to marine components is the most common mistake in this field. Aging in a marine environment is not simply UV aging—salt spray, humidity, and temperature cycling accumulate, causing additives to be depleted faster. There is a comparative study in the public domain worth remembering: PP samples soaked in natural seawater for a full 12 months only lost 0.65% of their weight (during the same period, LDPE lost 1.9% and HDPE 1.6%); while in another frequently cited set of data, the tensile properties of PE and PP after one year of seawater exposure decreased by approximately 12% and 26%, respectively (Pegram & Andrady 1989, cited in the review by Artham et al. 2009). The appearance hardly changes, the weight hardly increases, yet the mechanical strength drops by more than half—this is why marine components “look fine but crack under stress.”
3. ★ Selection Criteria Table: Eight indicators, each with verification methods and specifications
Pay attention to the third column — what often gets stuck is not 'which indicator to look at,' but 'what to measure and how much counts as passing.'
| Indicator | Threshold Value (Typical) | Verification Method / Standard | Common Failures | Common solution |
|---|
| Mechanical retention rate after seawater/salt fog aging | Elongation retention ≥80%, bending retention ≥75%, impact energy change within ±10 J (according to the public technical specification of the testing agency, Grade B); duration according to 24 / 48 / 96 h or as agreed with the customer | GB/T 10125-2021 'Artificial Atmosphere Corrosion Test Salt Spray Test' (5% NaCl, 35±2℃, pH 6.5-7.2); after aging, re-test retention rate according to GB/T 1040.2, GB/T 9341, GB/T 1043.1 | Surface pitting, brittleness, impact value cliff | Weather-resistant system mixed with anti-oxidation system, add carbon black if necessary |
| Low-temperature impact (cantilever beam notch) | −20℃ ≥93 J/m | Cantilever beam notch impact (ISO 180 / ASTM D256 caliber, Taihua K8003 material property table, Class B); measured after the specimen is placed for 16-24 hours | Cracking during winter and cold storage turnover | Impact-resistant copolymer substrate Increased toughening system dosage |
| Bending modulus | 900-1500 MPa | GB/T 9341 (Yanshan K4912, CNOOC Shell EP300M-Z physical property table caliber, Grade A) | Bulging when filled with water, collapsing under stacking pressure | Co-extrusion / Uniform extrusion grading Thin-walled with reinforcement |
| Water absorption and weight gain | Resin body 23℃/24h approximately 0.01% (Class B); the foamed core system is measured separately according to the 96 h immersion buoyancy method, and the overall door limit is agreed upon by customer acceptance. | GB/T 1034-2008 "Plastics — Determination of Water Absorption" (Method 1: 23℃/24h; Method 2: Boiling water 30 min); Foamed cores are tested according to GB/T 8810-2005 "Determination of Water Absorption of Rigid Foam Plastics" (immersed 50 mm under water for 96 h, buoyancy method) | Buoyancy decreases, the entire item gains weight, the box absorbs odors | Increase closed-cell rate, control moisture absorption of the filling, and leave drainage in the structure |
| Buoyancy and Pressure Resistance (Float Type) | Buoyancy by specification: Ø240 mm grade ≥6 N, Ø400 mm grade up to 30 N; pressure resistance is divided into three levels according to water depths of 150 / 200 / 300 m (1500-3000 kPa); crushing pressure is 1.33-2 times the working pressure. | SC/T 4050.2-2019 (Applicable to rigid spherical ABS floats, other types of floats can be referenced accordingly) SC/T 5002-2009 'Test Methods for Plastic Floats: Rigid Spherical' | Inlet leakage, insufficient pressure resistance leading to being crushed | Hollow structure, wall thickness design; or take the filled-shell approach |
| Carbon black content and UV resistance retention | Carbon black content ≥2.0%; UV resistance retention ≥90% | JT/T 1432.1-2022 (Soil geogrid aperture; for seawater components, refer to the two items 'carbon black strength retention') | After outdoor exposure, it powderizes, cracks, and its elongation drops sharply | Sufficient carbon black and light stabilizer blend |
| Ultraviolet Aging (Fluorescent Ultraviolet Lamp) | Color difference and mechanical retention are according to customer agreement; the industry practice is 500-1000 hours | GB/T 16422.3-2022 'Plastics — Laboratory light source exposure test methods — Part 3: Fluorescent ultraviolet lamps' | Fading, loss of gloss, surface powdering | Light Stabilizer System Weather-Resistant Grade Color Masterbatch |
| Appearance and performance retention after oil and dirt resistance and cleaning agent resistance | No loss of gloss or cracking after soaking/wiping, mechanical retention rate as agreed with the customer | Soak according to the list of media provided by the customer before testing the mechanical properties (there is no specific national threshold; the standard is subject to the customer’s agreement) | Sticky surface, cracking, label peeling off | Choose chemical-resistant base materials; avoid leaving stress concentrations on the parts |
Text Version Conclusion: Among the eight items, the two that should be looked at first are — mechanical retention after salt spray aging (determines if it can last) and −20℃ low-temperature impact (determines if it cracks in winter). Also, a reminder: there is no universal mandatory product standard for 'plastic parts used in aquaculture' in this field. The SC/T 4050.2-2019 and SC/T 5002-2009 for floating balls apply mainly to ABS rigid spherical floats; for aquaculture boxes and non-load-bearing marine components, acceptance criteria are more based on industry common practice and customer agreements. The purpose of the criteria table is to write in advance 'what to test and how to test' into the acceptance documents.
4. Common Failures and Root Causes: Four Phenomena, Four Root Causes
Failure 1: The corners of the box become brittle and crack with a single knock. The main cause is mostly insufficient low-temperature toughness, or the wall thickness thinning too quickly at the corners, causing stress concentration. First, check the wall thickness and fillets, then check the material; if the order is reversed, several rounds of replacements will be in vain.
Failure 2: Surface pitting, chalking, and fading. First, check whether there is a combination of UV and salt spray (salt spray according to GB/T 10125-2021, 5% NaCl, 35±2°C), then see if the amounts of carbon black and light stabilizers are sufficient. Doing only xenon lamp or UV tests without salt spray is the most common oversight for parts exposed to seawater.
Failure Three: After soaking for a full season, the whole piece becomes heavier and buoyancy decreases. The root cause is usually not in the resin—PP itself has a 23°C/24h water absorption rate of about 0.01%—but in the moisture absorption of the filler, water absorption by the core material, and water entering structural gaps. The order of inspection is: first, see if the structure has cavities and gaps where water can remain; then check the closed-cell rate of the core material; and only lastly, the resin.
Failure Four: Bulging after being filled with water for two days. This is a matter of bending modulus and creep, not 'soft material.' The bending modulus threshold is rated at 900-1500 MPa (Class A). If it is below this range and made with thin walls, bulging is inevitable.
There is one more easily overlooked point: focusing only on material selection for impact at room temperature while ignoring low-temperature embrittlement is the main cause of damage to breeding boxes in winter. Impact values that look good at room temperature may drop to a fraction at −20°C. You cannot rely on 'good room temperature data' to estimate low-temperature performance; it must be measured at −20°C.
5. Verification sequence: For parts resistant to seawater aging, what should be verified first and what should be verified later
Conclusion: The sequence is appearance → water absorption and density → mechanical properties after salt spray aging → low-temperature impact → full water load and hoisting → whole box drop. Skipping a step will result in the cost exploding at the end.
`
① Appearance and Color Difference Color swatch comparison, color difference, and loss of gloss
↓ However, just return the formula and color masterbatch
② Water absorption and density 23°C/24h, boiling water 30 min; foam core according to immersion 96 h buoyancy method
↓ But just revert to the filling system and core material
③ Mechanical retention after salt spray / damp heat aging GB/T 10125-2021, re-measure the retention rates of tensile, bending, and impact properties
If you don't pass this level, you don't need to do the rest.
④ Low-temperature impact −20°C cantilever beam notched impact, measured after the sample is placed for 16-24 hours
↓ However, it just returns to the toughening system and substrate grade
⑤ Full water load bearing and hoisting: Perform static loading and hoisting according to the actual loading amount and lifting points
↓ However, just revert to the structural and wall thickness design
⑥ Full box drop test Conduct according to the actual turnover height of the customer
`
The most common mistake is skipping steps ① and ② and going straight to ③—using a sample that has already absorbed water and has slightly changed color to evaluate aging resistance produces results that are not representative.
Text version of the conclusion: The mechanical test after salt spray must be done before load-bearing and drop tests — it is most likely to outright fail; only after passing it should we proceed with structural aspects, so as not to waste the cost of prototype testing.
6. Reverse Honesty: When these four conditions occur, float balls and plastic parts for boats should not use modified PP.
Earlier we talked about 'how to do it'; here we talk about 'when not to do it.' This section has the highest value for selection and judgment.
| The situation that occurred | Why is modified PP not suitable? | Which way should I go? |
|---|
| Structural load-bearing components, and require classification society (CC) certification | Modified PP is not in the regular list of materials of the classification society, and the certification path does not match. | Select materials according to classification society standards, using metal or fiberglass |
| Large-sized offshore buoy, long-term immersion in seawater and repeatedly impacted by waves | Mainstream materials and the publicly available technical requirements for local facility fisheries all point to HDPE; thick-walled rotational molding/blow molding forming methods are more suitable. | PE rotomolding or thick-wall blow molding |
| Floating parts such as trawl net floats, which need to withstand water pressure and repeated impacts | The applicable subject of SC/T 4050.2-2019 is ABS rigid spherical float; when PP is referenced for implementation, pressure resistance and impact resistance have to rely on structure and wall thickness to withstand. | ABS hard spherical float, or EPS-filled shell route |
| Requires metal-grade strength and long-term weather resistance | The modulus and creep of PP are structural, and can only be alleviated through modification. | Metal parts or fiberglass |
Consistent rule: Whenever the three conditions 'bearing strength, certification, long-term immersion in seawater' appear together, this part should not use modified PP. When encountering such a requirement, first make this clear before discussing whether there is any compromise—if you strictly proceed with the order, it will eventually need to be reworked and returned.
7. What to Move When Changing Materials: A First Review and Then Move Checklist for Aquaculture Box Components
After the customer decides to try modified PP, the real concern is often not the performance, but 'Do I need to change my current mold and process?'
| Items to move | What needs to be confirmed | What will happen if I don't do it? |
|---|
| Mold shrinkage rate | The publicly stated molding shrinkage rate of PP is 1%-2.5%, which is different from PE (1.5%-3.6%); long parts and large flat surfaces are particularly sensitive. | Dimensions out of tolerance, box lid does not close properly, assembly does not align |
| Gate and Venting | Breeding tanks are mostly large, thick-walled, or equipped with reinforced structures, with long processes and multiple vent points | Short shots, air burn, changes in weld line position |
| Material Temperature and Mold Temperature | The process windows of weatherable systems and toughening systems are different | Surface pitting, insufficient weld line strength |
| Dry | The filling system and foam core are sensitive to moisture | Silver threads, bubbles, localized brittleness |
| Pressure Holding and Demolding | Uneven shrinkage of thick-walled parts | Warping, shrinkage marks, pinholes |
| Color difference | The warning color items must first confirm the color swatch and weather resistance grade | After a few months outdoors, it fades into two batches of colors |
| Verification order | Appearance → Water absorption → Mechanical properties after salt spray → Low temperature impact → Load-bearing hoisting → Drop | All the risks are concentrated to explode at the final step |
Textual conclusion: The risk of material change in cultivation boxes is concentrated on uneven shrinkage in large thick-walled parts—warping and shrink marks are the most common, and are often mistakenly judged as 'material shrinkage.' The shrinkage rate itself is a design input; according to the number used in the mold design, it should be verified against that number when changing materials. Ribbed boxes also need to consider the rib positions—the root of the rib shrinks slowly, and shrink marks appear from there.
8. One-page report sheet (can be directly pasted into PPT)
| Scene | Recommended Route | Key indicators | Verification Standard | Conditions that need to be confirmed first |
|---|
| Aquaculture Box / Trough (Injection Molding) | Copolymer PP Weather-Resistant System | Bending modulus 900-1500 MPa; mechanical retention after aging | GB/T 9341; Salt spray according to GB/T 10125-2021 | Load capacity, number of stacking layers, minimum operating temperature |
| Cabinets and water-bearing components that need to be impact-resistant | Impact Copolymer PP Toughened | −20℃ cantilever beam notch impact ≥93 J/m | ISO 180 / ASTM D256; specimen placed for 16-24 h | Winter turnover temperature, wall thickness, and fillet |
| Non-load-bearing injection-molded parts for ships (grilles, protective plates, housings) | Copolymer PP Weather-resistant Antioxidant system | Mechanical retention after aging; carbon black content ≥2.0% | GB/T 10125-2021; JT/T 1432.1-2022 (referring to two items: carbon black and strength retention) | Whether it is submerged in water for a long time, and whether there is oil or cleaning agent |
| Small and medium-sized injection molded float ball housing | Copolymer PP (hollow structure) | Drop does not break, sealing and water absorption | Reference SC/T 4050.2-2019 for the buoyancy and impact resistance assessment criteria | Does the customer allow using PE or EPS filling route? |
| Large-Scale Offshore Buoy / Float | Modified PP is not recommended | — | — | See Section 6 Reverse Honesty Paragraph |
Text version conclusion: The purpose of this table is to allow technicians to report conclusions directly without having to reorganize their wording. There is only one criterion for judgment—whether the client can use this table to determine the direction of the materials in a single meeting.
9. The part of this piece that is most prone to problems is often not the material.
In the publicly available fishery technical requirements, the materials for parts such as buoys and pedals are specified in detail: virgin HDPE, no fillers, diameter not less than 500 mm, length not less than 900 mm, and minimum wall thickness not less than 3 mm; SC/T 4050.2-2019 sets hard standards for buoyancy thresholds, pressure resistance classification, and non-fragmentation from a 2 m drop. The common point is: 'structure, wall thickness, sealing' is placed before materials.
The criteria for aquaculture boxes and non-load-bearing marine components are closer to the material itself: the bending modulus falls in the 900-1500 MPa range, low-temperature impact is considered at −20°C, and mechanical retention is required after aging. The common industry practice is to determine these three things together—base material grade, toughening and weather-resistant system, and filler ratio. The balancing relationship among the three is the real technical difficulty; looking at any one aspect alone is meaningless.
The key is not about 'whose material is better,' but whether the four aspects—substrate grade, toughening system, weather resistance system, and structure and wall thickness—can all match simultaneously.
Ningbo Kolon New Materials Co., Ltd. commonly supplies modified polypropylene (PP) particles in the areas of copolymer and impact copolymer. They provide corresponding base material grades and weather resistance and toughening systems based on the operating temperature of the part, whether it will be long-term immersed in water, and the wall thickness distribution. This is mainly used to address the two issues mentioned above: 'low-temperature cracking and rapid mechanical property degradation after aging.' The formulations can be adjusted according to the working conditions of the parts, and can be used for small sample comparison and trial molding. They can also accommodate part-level customers' demands for multiple varieties in small batches.
Frequently Asked Questions
Q: Can the float ball actually be made of PP?
Answer: It depends on the specifications and the approach. According to publicly available information, there are trawl net floats with PP spheres and EPS filling; these are medium to small in size and rely on foam to provide buoyancy. Large offshore floats and buoys, according to publicly available fishery technical requirements, are made from virgin HDPE. PP can be used for medium to small hollow-structured shells, but if ruptured, water will enter; using the foam-filling approach, even if the shell is damaged, there is still internal buoyancy.
Question: Is the feed in the breeding tank better if it is tougher?
Answer: No. Toughness and rigidity here refer to tensile properties—toughening agents are added to prevent cracking at low temperatures, which will reduce the bending modulus, making it easy to bulge when filled with water. The correct approach is to first set the bending modulus level (corresponding to load capacity and stacking layers), and then use a toughening system to raise the low-temperature impact above the threshold.
Question: If the item is only used in inland rivers, does it still need to undergo a salt spray test?
Answer: It should be done whenever it comes into contact with seawater. The neutral salt spray test according to GB/T 10125-2021 uses 5% NaCl, 35±2℃, pH 6.5-7.2, and the duration is 24/48/96 hours or as agreed with the customer. Only doing UV testing and skipping salt spray is the most common omission for seawater parts, and the part that is skipped is precisely the one where additives are consumed the fastest.
| Operating condition | Key criterion | Cologne regular supply |
|---|
| Breeding Box / Trough (Injection Molding) | Bending modulus 900-1500 MPa; mechanical retention after aging | Co-polymer PP Weather-Resistant System Direction |
| Impact-resistant casing and water-bearing components | −20℃ cantilever beam notch impact | Impact Copolymer PP Toughening Direction |
| Non-structural ship components | Mechanical retention after salt spray; carbon black content | Copolymer PP Weather-Resistant and Anti-Oxidation System Direction |
I want to give a reminder: when there is a problem with marine parts, the most common mistake is to change the material first. Brittleness, swelling, fading, weight gain—each issue has more than one cause. Identify the cause first, then change the material; if the order is reversed, even after several rounds of replacement, the problem often remains.
Ten, Lastly, say three sentences
First, ask whether this item is 'long-term immersed in seawater and load-bearing.' If it meets both conditions, modified PP is usually not the first choice; if it only meets one condition, then it is worth discussing.
Secondly, the threshold for seawater components should fall on the words 'after aging.' Having good initial indicators does not mean it can be used reliably; what truly reflects the real lifespan is how much remains after salt spray and humidity heat exposure.
Third, the verification order is more important than the verification items. Appearance → Water absorption → Mechanical properties after salt spray → Low-temperature impact → Load-bearing lifting → Drop test; the mechanical properties after salt spray must be scheduled before load-bearing and drop tests.
For the next article, change to another piece, and continue to break down according to the four layers: working conditions, route, criteria, and validation.
About Us
Let's talk about three things before quoting: where this part will be used, which requirements it has, and which ones can be dropped.
Especially the third point. The indicators of modified PP are not additive; they are trade-offs—flame retardancy versus toughness, high flow versus impact resistance, glass fiber versus dimensional stability. Without ranking them, you can't quote a price accurately, nor can you stabilize the plan.
Ningbo Cologne New Materials Co., Ltd. produces modified polypropylene (PP) granules, covering homopolymer, random copolymer, and block copolymer base materials, as well as modifications including filled, glass fiber reinforced, toughened, flame-retardant, low odor and low VOC, weather-resistant, and scratch-resistant without coating; it also deals in PP resins from major petrochemical plants, off-spec materials, and bulk materials.
