橡胶树初生乳管橡胶的产量性状与橡胶特性研究

巴西橡胶树（Hevea brasiliensis）的乳管分初生乳管和次生乳管2种类型，前者分布在叶片和初生生长茎干的皮组织，后者分布在次生生长茎干的皮组织。目前，商用橡胶主要来自次生乳管，关于次生乳管橡胶的认识较透彻；由于初生乳管橡胶未被开发利用，因此人们对其了解也较少。以来自橡胶嫁接幼树枝叶的初生乳管橡胶为研究对象，通过分析与初生乳管橡胶产量相关的因子，包括枝叶生物量、生物量组成和橡胶含量等，明确初生乳管橡胶的产量潜力。同时，还研究了初生乳管橡胶的生胶性能和硫化特性。结果表明，橡胶幼树枝叶的生物量、生物量组成和橡胶含量因无性系而异，受无性系影响。在枝叶生物量组成中，叶片、树皮和木质杆分别占枝叶生物量的55.5%、10.5%和34.0%。叶片和树皮的橡胶含量分别为每克干物质含橡胶13.7和35.6 mg。初生乳管胶乳的橡胶粒子平均粒径（0.36 μm）和相对分子量低于常规割胶树的胶乳橡胶。初生乳管橡胶的氮含量和PRI分别为0.56%和89%，均高于常规橡胶的氮含量（0.50%）和PRI（80%）。初生乳管橡胶的门尼粘度和塑性初值P₀分别为66和26，均低于常规橡胶的门尼粘度（101）和P₀（50）。初生乳管橡胶的挥发份和灰分含量均与常规橡胶相同，分别为0.50%和0.38%。初生乳管橡胶的初始硫化时间T₁₀为2.00 min，正硫化时间T₉₀为19.12 min，均比常规橡胶的T₁₀ 2.47和T₉₀ 25.08硫化时间短。初生乳管橡胶硫化曲线的最小扭矩较小（0.22 dN·m），而最大扭矩较大（8.25 dN·m）。通过分析3个无性系材料，结果表明萌条枝叶生物量、生物量组成和橡胶含量具有品系特征，并影响初生乳管橡胶产量，这为初生乳管橡胶在资源育种与栽培技术指明了研究方向。鉴于初生乳管橡胶的门尼粘度和P₀达不到标准胶要求，但其他理化性能指标与常规橡胶相似，建议初生乳管橡胶不能作为标准胶使用，但可作为普通胶料用于生产。

Quantification and Characterization of Rubber from Primary Laticifers of Hevea brasiliensis

Hevea brasiliensis contains two types of laticifers, primary and secondary. The former distributes in the leaf and bark of stems with primary growth, and the latter distributes in the bark of stems with secondary growth. The commercial rubber is extracted from the latex of secondary laticifers and much is known to this rubber. However, little is known to the rubber in primary laticifers as it has not been exploited. This study focused on the rubber from primary laticifers from young shoots of grafted plants. We evaluated the rubber yield-related factors, including shoot biomass, biomass partitioning, and rubber content, to determine rubber yield potential. In addition, we characterized the physical and chemical properties and vulcanization behavior of raw rubbers. Results showed that clones could affect shoot biomass, biomass partitioning, and rubber content. On average, biomass partitioning value for the leaf, bark and wood was 55.5%, 10.5%, and 34.0%, respectively. Rubber content in the leaf and bark was 13.7 and 35.6 mg/g dry weight, respectively. The rubber particle average size of the latex from primary laticifers was 0.36 μm, smaller than that from secondary laticifers. Rubber from primary laticifers had a smaller molecular weight than that from conventionally tapped mature trees. The nitrogen content of rubber from primary laticifers was 0.56%, higher than that of conventional rubber (0.50%). The plasticity retention index (PRI) of rubber from primary laticifers was 89%, higher than that of conventional rubber (80%). However, the Mooney viscosity and initial plasticity (P₀) of the rubber from primary laticifers was 66 and 26, respectively, lower than that of conventional rubber (101 and 50, respectively). The volatile matter content and the ash content of rubber from primary laticifers was 0.50% and 0.38%, respectively, the same as that of conventional rubber. The scorching T₁₀ and optimal vulcanization T₉₀ times of the rubber from primary laticifers was 2.00 and 19.12 min, respectively, which was lower than conventional rubber (2.47 and 25.08 min, respectively). Comparing to conventional rubber, rubber from primary laticifers exhibited a lower minimum torque (M_L) value (0.22 dN·m), but a higher maximum torque (M_H) value (8.25 dN·m). By analyzing three clones, the results suggest that the rubber yield from primary laticifers from young shoots could be affected by shoot biomass, biomass partitioning and rubber contents. This rubber yield related results would provide a foundation for future work on breeding, germplasm development and cultivation practices. The results on rubber property showed that the rubber from primary laticifers was comparable to conventional rubber except for Mooney viscosity and P₀, suggesting that the rubber from primary laticifers could not be used as standard rubber but general rubber material.